CaltechAUTHORS: Article
https://feeds.library.caltech.edu/people/Ramsey-Musolf-M-J/article.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 24 May 2024 19:48:56 -0700Anapole moment and other constraints on the strangeness conserving hadronic weak interaction
https://resolver.caltech.edu/CaltechAUTHORS:HAXprl01
Year: 2001
DOI: 10.1103/PhysRevLett.86.5247
Standard analyses of low-energy NN and nuclear parity-violating observables have been based on a π-, ρ-, and ω-exchange model capable of describing all five independent s-p partial waves. Here a parallel analysis is performed for the one-body, exchange-current, and nuclear polarization contributions to the anapole moments of 133Cs and 205Tl. The resulting constraints are not consistent, though there remains some degree of uncertainty in the nuclear structure analysis of the atomic moments.https://resolver.caltech.edu/CaltechAUTHORS:HAXprl01Subleading corrections to parity-violating pion photoproduction
https://resolver.caltech.edu/CaltechAUTHORS:ZHUprc01
Year: 2001
DOI: 10.1103/PhysRevC.64.035502
We compute the photon asymmetry Bγ for near threshold parity-violating (PV) pion photoproduction through subleading order. We show that subleading contributions involve a new combination of PV couplings not included in previous analyses of hadronic PV. We argue that existing constraints on the leading order contribution to Bγ—obtained from the PV γ-decay of 18F—suggest that the impact of the subleading contributions may be more significant than expected from naturalness arguments.https://resolver.caltech.edu/CaltechAUTHORS:ZHUprc01Parity-Violating Photoproduction of π± on the Δ Resonance
https://resolver.caltech.edu/CaltechAUTHORS:ZHUprl01
Year: 2001
DOI: 10.1103/PhysRevLett.87.201802
We analyze the real-photon asymmetry Aγ± for the parity-violating (PV) π± production on the Δ resonance via the reactions γ→+p→Δ+→π++n and γ→+d→Δ0+p→π-+p+p. This asymmetry is nonvanishing due to a PV γNΔ coupling constant, dΔ±. We argue that an experimental determination of this coupling would be of interest for hadron dynamics, possibly shedding light on the S-wave/ P-wave puzzle in the hyperon nonleptonic decays and the violation of Hara's theorem in weak radiative hyperon decays.https://resolver.caltech.edu/CaltechAUTHORS:ZHUprl01Electroweak radiative corrections to parity-violating electroexcitation of the Δ
https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02c
Year: 2002
DOI: 10.1103/PhysRevD.65.033001
We analyze the degree to which parity-violating (PV) electroexcitation of the Δ(1232) resonance may be used to extract the weak neutral axial vector transition form factors. We find that the axial vector electroweak radiative corrections are large and theoretically uncertain, thereby modifying the nominal interpretation of the PV asymmetry in terms of the weak neutral form factors. We also show that, in contrast with the situation for elastic electron scattering, the axial N→Δ PV asymmetry does not vanish at the photon point as a consequence of a new term entering the radiative corrections. We argue that an experimental determination of these radiative corrections would be of interest for hadron structure theory, possibly shedding light on the violation of Hara's theorem in weak, radiative hyperon decays.https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02cCharged current universality in the minimal supersymmetric standard model
https://resolver.caltech.edu/CaltechAUTHORS:KURprl02
Year: 2002
DOI: 10.1103/PhysRevLett.88.071804
We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the minimal supersymmetric standard model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current data are analyzed in tandem with measurements of the muon anomaly. While the data allow the presence of at least one light neutralino, they also imply a pattern of mass splittings among first and second generation sleptons and squarks which contradicts predictions of widely used models for supersymmetry-breaking mediation.https://resolver.caltech.edu/CaltechAUTHORS:KURprl02Nuclear anapole moments
https://resolver.caltech.edu/CaltechAUTHORS:HAXprc02
Year: 2002
DOI: 10.1103/PhysRevC.65.045502
Nuclear anapole moments are parity-odd, time-reversal-even E1 moments of the electromagnetic current operator. Although the existence of this moment was recognized theoretically soon after the discovery of parity nonconservation (PNC), its experimental isolation was achieved only recently, when a new level of precision was reached in a measurement of the hyperfine dependence of atomic PNC in 133Cs. An important anapole moment bound in 205Tl also exists. In this paper, we present the details of the first calculation of these anapole moments in the framework commonly used in other studies of hadronic PNC, a meson-exchange potential that includes long-range pion exchange and enough degrees of freedom to describe the five independent S-P amplitudes induced by short-range interactions. The resulting contributions of π, ρ, and ω exchange to the single-nucleon anapole moment, to parity admixtures in the nuclear ground state, and to PNC exchange currents are evaluated, using configuration-mixed shell-model wave functions. The experimental anapole moment constraints on the PNC meson-nucleon coupling constants are derived and compared with those from other tests of the hadronic weak interaction. While the bounds obtained from the anapole moment results are consistent with the broad "reasonable ranges" defined by theory, they are not in good agreement with the constraints from the other experiments. We explore possible explanations for the discrepancy and comment on the potential importance of new experiments.https://resolver.caltech.edu/CaltechAUTHORS:HAXprc02Radiative corrections in neutrino-deuterium disintegration
https://resolver.caltech.edu/CaltechAUTHORS:KURprc02
Year: 2002
DOI: 10.1103/PhysRevC.65.055501
The radiative corrections of order alpha for the charged- and neutral-current neutrino-deuterium disintegration for energies relevant to the SNO experiment are evaluated. Particular attention is paid to the issue of the bremsstrahlung detection threshold. It is shown that the radiative corrections to the total cross section for the charged current reaction are independent of that threshold, as they must be for consistency, and amount to a slowly decreasing function of the neutrino energy E-nu, varying from about 4% at low energies to 3% at the end of the B-8 spectrum. The differential cross section corrections, on the other hand, do depend on the bremsstrahlung detection threshold. Various choices of the threshold are discussed. It is shown that for a realistic choice of the threshold and for the actual electron energy threshold of the SNO detector, the deduced B-8 nu(e) flux should be decreased by about 2%. The radiative corrections to the neutral-current reaction are also evaluated.https://resolver.caltech.edu/CaltechAUTHORS:KURprc02Hadronic Light-by-Light Contribution to Muon g - 2 in Chiral Perturbation Theory
https://resolver.caltech.edu/CaltechAUTHORS:RAMprl02
Year: 2002
DOI: 10.1103/PhysRevLett.89.041601
We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, aμLL(had), in chiral perturbation theory that are enhanced by large logarithms and a factor of NC. They depend on a low-energy constant constrained by η→μ+μ- and π0→e+e- branching ratios. However, the dependence of aμLL(had) on nonlogarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself.https://resolver.caltech.edu/CaltechAUTHORS:RAMprl02Recoil order chiral corrections to baryon octet axial vector currents and large Nc QCD
https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02b
Year: 2002
DOI: 10.1103/PhysRevD.66.034021
We compute the chiral corrections to octet baryon axial vector currents through O(p3) in heavy baryon chiral perturbation theory, including both octet and decuplet baryon intermediate states. We include the latter in a consistent way by using the small scale expansion. We find that, in contrast to the situation at O(p2), there exist no cancellations between octet and decuplet contributions at O(p3). Consequently, the O(p3) corrections spoil the expected scaling behavior of the chiral expansion. We discuss this result in terms of the 1/Nc expansion. We also consider the implications for the determination of the strange quark contribution to the nucleon spin from polarized deep inelastic scattering data.https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02bOff-diagonal Goldberger-Treiman relation and its discrepancy
https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02a
Year: 2002
DOI: 10.1103/PhysRevD.66.076008
We study the off-diagonal Goldberger-Treiman relation (ODGTR) and its discrepancy (ODGTD) in the N, Δ, π sector through O(p2) using heavy baryon chiral perturbation theory. To this order, the ODGTD and axial vector N to Δ transition radius are determined solely by low-energy constants. Loop corrections appear at O(p4). For low-energy constants of natural size, the ODGTD would represent a ∼2% correction to the ODGTR. We discuss the implications of the ODGTR and ODGTD for lattice and quark model calculations of the transition form factors and for parity-violating electroexcitation of the Δ.https://resolver.caltech.edu/CaltechAUTHORS:ZHUprd02aHadronic parity violation and inelastic electron-deuteron scattering
https://resolver.caltech.edu/CaltechAUTHORS:LIUprc03
Year: 2003
DOI: 10.1103/PhysRevC.67.035501
We compute contributions to the parity-violating (PV) inelastic electron-deuteron scattering asymmetry arising from hadronic PV. While hadronic PV effects can be relatively important in PV threshold electrodisintegration, we find that they are highly suppressed at quasielastic kinematics. The interpretation of the PV quasielastic asymmetry is, thus, largely unaffected by hadronic PV.https://resolver.caltech.edu/CaltechAUTHORS:LIUprc03Radiative corrections to low-energy neutrino reactions
https://resolver.caltech.edu/CaltechAUTHORS:KURprc03
Year: 2003
DOI: 10.1103/PhysRevC.67.035502
We show that the radiative corrections to charged current (CC) nuclear reactions with an electron (positron) in the final state are described by a universal function. The consistency of our treatment of the radiative corrections with the procedure used to extract the value of the axial coupling constant g(A) is discussed. To illustrate we apply our results to (anti) neutrino deuterium disintegration and to pp fusion in the sun. The limit of vanishing electron mass is considered, and a simple formula sufficiently accurate for E(obs)greater than or similar to 1 MeV is obtained. The size of the nuclear structure-dependent effects is also discussed. Finally, we consider CC transitions with an electron (positron) in the initial state and discuss some applications to electron capture reactions.https://resolver.caltech.edu/CaltechAUTHORS:KURprc03Weak charge of the proton and new physics
https://resolver.caltech.edu/CaltechAUTHORS:ERLprd03
Year: 2003
DOI: 10.1103/PhysRevD.68.016006
We address the physics implications of a precise determination of the weak charge of the proton, QW(p), from a parity violating elastic electron proton scattering experiment to be performed at the Jefferson Laboratory. We present the standard model (SM) expression for QW(p) including one-loop radiative corrections, and discuss in detail the theoretical uncertainties and missing higher order QCD corrections. Owing to a fortuitous cancellation, the value of QW(p) is suppressed in the SM, making it a unique place to look for physics beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and leptoquarks. We argue that a QW(p) measurement will provide an important complement to both high energy collider experiments and other low energy electroweak measurements. The anticipated experimental precision requires the knowledge of the O(alphas) corrections to the pure electroweak box contributions. We compute these contributions for QW(p), as well as for the weak charges of heavy elements as determined from atomic parity violation.https://resolver.caltech.edu/CaltechAUTHORS:ERLprd03Neutrinoless double beta decay and effective field theory
https://resolver.caltech.edu/CaltechAUTHORS:PREprd03
Year: 2003
DOI: 10.1103/PhysRevD.68.034016
We analyze neutrinoless double beta decay (0nubetabeta decay) mediated by heavy particles from the standpoint of effective field theory. We show how symmetries of the 0nubetabeta-decay quark operators arising in a given particle physics model determine the form of the corresponding effective, hadronic operators. We classify the latter according to their symmetry transformation properties as well as the order at which they appear in a derivative expansion. We apply this framework to several particle physics models, including R-parity violating supersymmetry (RPV SUSY) and the left-right symmetric model (LRSM) with mixing and a right-handed Majorana neutrino. We show that, in general, the pion exchange contributions to 0nubetabeta decay dominate over the short-range four-nucleon operators. This confirms previously published RPV SUSY results and allows us to derive new constraints on the masses in the LRSM. In particular, we show how a nonzero mixing angle zeta in the left-right symmetry model produces a new potentially dominant contribution to 0nubetabeta decay that substantially modifies previous limits on the masses of the right-handed neutrino and boson stemming from constraints from 0nubetabeta decay and vacuum stability requirements.https://resolver.caltech.edu/CaltechAUTHORS:PREprd03Probing supersymmetry with parity-violating electron scattering
https://resolver.caltech.edu/CaltechAUTHORS:KURprd03
Year: 2003
DOI: 10.1103/PhysRevD.68.035008
We compute the one-loop supersymmetric (SUSY) contributions to the weak charges of the electron (QWe), proton (QWp), and cesium nucleus (QWCs) in the minimal supersymmetric standard model (MSSM). Such contributions can generate several percent corrections to the corresponding standard model values. The magnitudes of the SUSY loop corrections to QWe and QWp are correlated over nearly all of the MSSM parameter space and result in an increase in the magnitudes of these weak charges. In contrast, the effects on QWCs are considerably smaller and are equally likely to increase or decrease its magnitude. Allowing for R-parity violation can lead to opposite sign relative shifts in QWe and QWp, normalized to the corresponding standard model values. A comparison of QWp and QWe measurements could help distinguish between different SUSY scenarios.https://resolver.caltech.edu/CaltechAUTHORS:KURprd03Lepton flavor violation without supersymmetry
https://resolver.caltech.edu/CaltechAUTHORS:CIRprd04
Year: 2004
DOI: 10.1103/PhysRevD.70.075007
We study the lepton flavor-violating (LFV) processes µ-->egamma, µ-->3e, and µ-->e conversion in nuclei in the left-right symmetric model without supersymmetry and perform the first complete computation of the LFV branching ratios B(µ-->f) to leading nontrivial order in the ratio of left- and right-handed symmetry-breaking scales. To this order, B(µ-->egamma) and B(µ-->e) are governed by the same combination of LFV violating couplings, and their ratio is naturally of order unity. We also find B(µ-->3e)/B(µ-->e)~100 under slightly stronger assumptions. Existing limits on the branching ratios already substantially constrain mass splittings and/or mixings in the heavy neutrino sector. When combined with future collider studies and precision electroweak measurements, improved limits on LFV processes will test the viability of low-scale, nonsupersymmetric LFV scenarios.https://resolver.caltech.edu/CaltechAUTHORS:CIRprd04Vector analyzing power in elastic electron-proton scattering
https://resolver.caltech.edu/CaltechAUTHORS:DIAprc04
Year: 2004
We compute the vector analyzing power (VAP) for the elastic scattering of transversely polarized electrons from protons at low energies using an effective theory of electrons, protons, and photons. We study all contributions through second order in E/M, where E and M are the electron energy and nucleon mass, respectively. The leading-order VAP arises from the imaginary part of the interference of one- and two-photon exchange amplitudes. Subleading contributions are generated by the nucleon magnetic moment and charge radius as well as recoil corrections to the leading-order amplitude. Working to O(E/M)the 2nd , we obtain a prediction for An that is free of unknown parameters and that agrees with the recent measurement of the VAP in backward angle ep scattering.https://resolver.caltech.edu/CaltechAUTHORS:DIAprc04Neutrinoless Double Beta Decay and Lepton Flavor Violation
https://resolver.caltech.edu/CaltechAUTHORS:CIRprl04
Year: 2004
DOI: 10.1103/PhysRevLett.93.231802
We point out that extensions of the standard model with low scale (~TeV) lepton number violation (LNV) generally lead to a pattern of lepton flavor violation (LFV) experimentally distinguishable from the one implied by models with grand unified theory scale LNV. As a consequence, muon LFV processes provide a powerful diagnostic tool to determine whether or not the effective neutrino mass can be deduced from the rate of neutrinoless double beta decay. We discuss the role of µ-->egamma and µ-->e conversion in nuclei, which will be studied with high sensitivity in forthcoming experiments.https://resolver.caltech.edu/CaltechAUTHORS:CIRprl04Parity-violation with electrons: Theoretical perspectives
https://resolver.caltech.edu/CaltechAUTHORS:20110804-114221939
Year: 2005
DOI: 10.1140/epjad/s2005-04-049-3
I review recent progress and developments in parity-violating electron scattering as it bears on three topics: strange quarks and hadron structure, electroweak radiative corrections, and physics beyond the Standard Model. I also discuss related developments in parity-conserving scattering with transversely polarized electrons as a probe of two-photon processes. I conclude with a perspective on the future of the field.https://resolver.caltech.edu/CaltechAUTHORS:20110804-114221939Resonant relaxation in electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:LEEprd05
Year: 2005
DOI: 10.1103/PhysRevD.71.075010
We compute the leading, chiral charge-changing relaxation term in the quantum transport equations that govern electroweak baryogenesis using the closed time path formulation of nonequilibrium quantum field theory. We show that the relaxation transport coefficients may be resonantly enhanced under appropriate conditions on electroweak model parameters and that such enhancements can mitigate the impact of similar enhancements in the CP-violating source terms. We also develop a power counting in the time and energy scales entering electroweak baryogenesis and include effects through second order in ratios epsilon of the small and large scales. We illustrate the implications of the resonantly enhanced [script O](epsilon 2) terms using the Minimal Supersymmetric Standard Model, focusing on the interplay between the requirements of baryogenesis and constraints obtained from collider studies, precision electroweak data, and electric dipole moment searches.https://resolver.caltech.edu/CaltechAUTHORS:LEEprd05Weak mixing angle at low energies
https://resolver.caltech.edu/CaltechAUTHORS:ERLprd05
Year: 2005
DOI: 10.1103/PhysRevD.72.073003
We determine the weak mixing angle in the (MS) over bar scheme, sin(2)(theta) over cap (W)(mu), at energy scales mu relevant for present and future low-energy electroweak measurements. We relate the renormalization group evolution of sin(2)(theta) over cap (W)(mu) to the corresponding evolution of (alpha) over cap(mu) and include higher-order terms in alpha(s) and alpha that had not been treated in previous analyses. We also update the analysis of nonperturbative, hadronic contributions and argue that the associated uncertainty is small compared to anticipated experimental errors. The resulting value of the low-energy (MS) over bar weak mixing angle is sin(2)(theta) over cap (W)(0)=0.23867 +/- 0.00016.https://resolver.caltech.edu/CaltechAUTHORS:ERLprd05How Magnetic is the Dirac Neutrino?
https://resolver.caltech.edu/CaltechAUTHORS:BELprl05
Year: 2005
DOI: 10.1103/PhysRevLett.95.151802
We derive model-independent, "naturalness" upper bounds on the magnetic moments µnu of Dirac neutrinos generated by physics above the scale of electroweak symmetry breaking. In the absence of fine-tuning of effective operator coefficients, we find that current information on neutrino mass implies that |µnu|<~10-14 bohr magnetons. This bound is several orders of magnitude stronger than those obtained from analyses of solar and reactor neutrino data and astrophysical observations.https://resolver.caltech.edu/CaltechAUTHORS:BELprl05Yukawa and triscalar processes in electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:CIRprd06a
Year: 2006
DOI: 10.1103/PhysRevD.73.115009
We derive the contributions to the quantum transport equations for electroweak baryogenesis due to decays and inverse decays induced by triscalar and Yukawa interactions. In the minimal supersymmetric standard model (MSSM), these contributions give rise to couplings between Higgs and fermion supermultiplet densities, thereby communicating the effects of CP-violation in the Higgs sector to the baryon sector. We show that the decay and inverse decay-induced contributions that arise at zeroth order in the strong coupling, alphas, can be substantially larger than the [script O](alphas) terms that are generated by scattering processes and that are usually assumed to dominate. We revisit the often-used approximation of fast Yukawa-induced processes and show that for realistic parameter choices it is not justified. We solve the resulting quantum transport equations numerically with special attention to the impact of Yukawa rates and study the dependence of the baryon-to-entropy ratio YB on MSSM parameters.https://resolver.caltech.edu/CaltechAUTHORS:CIRprd06aHadronic Parity Violation: A New View Through the Looking Glass
https://resolver.caltech.edu/CaltechAUTHORS:RAMarnps06
Year: 2006
DOI: 10.1146/annurev.nucl.54.070103.181255
Studies of the strangeness-changing hadronic weak interaction have produced a number of puzzles that have evaded a complete explanation within the Standard Model. Their origin may lie either in dynamics peculiar to weak interactions involving strange quarks or in more general aspects of the interplay between strong and weak interactions. In principle, studies of the strangeness-conserving hadronic weak interaction using parity-violating hadronic and nuclear observables provide a complementary window to this question. However, progress in this direction has been hampered by the lack of a suitable theoretical framework for interpreting hadronic parity violation measurements in a model-independent way. Recent work involving effective field theory ideas has led to the formulation of such a framework, simultaneously motivating the development of a number of new hadronic parity violation experiments in few-body systems. We review these recent developments and discuss the prospects and opportunities for further experimental and theoretical progress.https://resolver.caltech.edu/CaltechAUTHORS:RAMarnps06Neutrino mass implications for muon decay parameters
https://resolver.caltech.edu/CaltechAUTHORS:ERWprd07
Year: 2007
DOI: 10.1103/PhysRevD.75.033005
We use the scale of neutrino mass and naturalness considerations to obtain model-independent expectations for the magnitude of possible contributions to muon decay Michel parameters from new physics above the electroweak symmetry-breaking scale. Focusing on Dirac neutrinos, we obtain a complete basis of dimension four and dimension six effective operators that are invariant under the gauge symmetry of the standard model and that contribute to both muon decay and neutrino mass. We show that—in the absence of fine tuning—the most stringent neutrino-mass naturalness bounds on chirality-changing vector operators relevant to muon decay arise from one-loop operator mixing. The bounds we obtain on their contributions to the Michel parameters are 2 orders of magnitude stronger than bounds previously obtained in the literature. In addition, we analyze the implications of one-loop matching considerations and find that the expectations for the size of various scalar and tensor contributions to the Michel parameters are considerably smaller than derived from previous estimates of two-loop operator mixing. We also show, however, that there exist gauge-invariant operators that generate scalar and tensor contributions to muon decay but whose flavor structure allows them to evade neutrino-mass naturalness bounds. We discuss the implications of our analysis for the interpretation of muon-decay experiments.https://resolver.caltech.edu/CaltechAUTHORS:ERWprd07Minimal extension of the standard model scalar sector
https://resolver.caltech.edu/CaltechAUTHORS:OCOprd07
Year: 2007
DOI: 10.1103/PhysRevD.75.037701
The minimal extension of the scalar sector of the standard model contains an additional real scalar field with no gauge quantum numbers. Such a field does not couple to the quarks and leptons directly but rather through its mixing with the standard model Higgs field. We examine the phenomenology of this model focusing on the region of parameter space where the new scalar particle is significantly lighter than the usual Higgs scalar and has small mixing with it. In this region of parameter space most of the properties of the additional scalar particle are independent of the details of the scalar potential. Furthermore the properties of the scalar that is mostly the standard model Higgs can be drastically modified since its dominant branching ratio may be to a pair of the new lighter scalars.https://resolver.caltech.edu/CaltechAUTHORS:OCOprd07Supersymmetric contributions to weak decay correlation coefficients
https://resolver.caltech.edu/CaltechAUTHORS:PROprd07b
Year: 2007
DOI: 10.1103/PhysRevD.75.075017
We study supersymmetric contributions to correlation coefficients that characterize the spectral shape and angular distribution for polarized µ- and beta-decays. In the minimal supersymmetric standard model (MSSM), one-loop box graphs containing superpartners can give rise to non-(V-A)[direct-product](V-A) four-fermion operators in the presence of left-right or flavor mixing between sfermions. We analyze the present phenomenological constraints on such mixing and determine the range of allowed contributions to the weak decay correlation coefficients. We discuss the prospective implications for future µ- and beta-decay experiments, and argue that they may provide unique probes of left-right mixing in the first generation scalar fermion sector.https://resolver.caltech.edu/CaltechAUTHORS:PROprd07bFuture directions in parity violation: From quarks to the cosmos
https://resolver.caltech.edu/CaltechAUTHORS:20101008-113258993
Year: 2007
DOI: 10.1140/epja/i2006-10413-1
I discuss the prospects for future studies of parity-violating (PV) interactions at low energies and the insights they might provide about open questions in the standard model as well as physics that lies beyond it. I cover four types of parity-violating observables: PV electron scattering; PV hadronic interactions; PV correlations in weak decays and searches for the permanent electric dipole moments of quantum systems.https://resolver.caltech.edu/CaltechAUTHORS:20101008-113258993Global analysis of nucleon strange form factors at low Q^2
https://resolver.caltech.edu/CaltechAUTHORS:LIUprc07
Year: 2007
DOI: 10.1103/PhysRevC.76.025202
We perform a global analysis of all recent experimental data from elastic parity-violating electron scattering at low Q^2. The values of the electric and magnetic strange form factors of the nucleon are determined at Q^2=0.1 GeV/c^2 to be G<sub>E</sub><sup>s</sup>=-0.008±0.016 and G<sub>M</sub><sup>s</sup>=0.29±0.21.https://resolver.caltech.edu/CaltechAUTHORS:LIUprc07Singlet Higgs phenomenology and the electroweak phase transition
https://resolver.caltech.edu/CaltechAUTHORS:PROjhep07
Year: 2007
DOI: 10.1088/1126-6708/2007/08/010
We study the phenomenology of gauge singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. We determine the conditions on the scalar potential parameters that lead to a strong first order phase transition as needed to produce the observed baryon asymmetry of the universe. We analyze the constraints on the potential parameters derived from Higgs boson searches at LEP and electroweak precision observables. For models that satisfy these constraints and that produce a strong first order phase transition, we discuss the prospective signatures in future Higgs studies at the Large Hadron Collider and a Linear Collider. We argue that such studies will provide powerful probes of phase transition dynamics in models with an extended scalar sector.https://resolver.caltech.edu/CaltechAUTHORS:PROjhep07Atomic electric dipole moments: The Schiff theorem and its corrections
https://resolver.caltech.edu/CaltechAUTHORS:LIUprc07b
Year: 2007
DOI: 10.1103/PhysRevC.76.035503
Searches for the permanent electric dipole moments (EDMs) of diamagnetic atoms provide powerful probes of CP-violating hadronic and semileptonic interactions. The theoretical interpretation of such experiments, however, requires careful implementation of a well-known theorem by Schiff that implies a vanishing net EDM for an atom built entirely from pointlike, nonrelativistic constituents that interact only electrostatically. Any experimental observation of a nonzero atomic EDM would result from corrections to the pointlike, nonrelativistic, electrostatic assumption. We reformulate Schiff's theorem at the operator level and delineate the electronic and nuclear operators whose atomic matrix elements generate corrections to "Schiff screening." We obtain a form for the operator responsible for the leading correction associated with finite nuclear size—the so-called Schiff moment operator—and observe that it differs from the corresponding operator used in previous Schiff moment computations. We show that the more general Schiff moment operator reduces to the previously employed operator only under certain approximations that are not generally justified. We also identify other corrections to Schiff screening that may not be included properly in previous theoretical treatments. We discuss practical considerations for obtaining a complete computation of corrections to Schiff screening in atomic EDM calculations.https://resolver.caltech.edu/CaltechAUTHORS:LIUprc07bFermionic effective operators and Higgs production at a linear collider
https://resolver.caltech.edu/CaltechAUTHORS:KILprd07
Year: 2007
DOI: 10.1103/PhysRevD.76.054009
We study the possible contributions of dimension six operators containing fermion fields to Higgs production at a 500 GeV or 1 TeV e+e- linear collider. We show that—depending on the production mechanism—the effects of such operators can be kinematically enhanced relative to standard model (SM) contributions. We determine constraints on the operator coefficients implied by existing precision electroweak measurements and the scale of neutrino mass. We find that even in the presence of such constraints, substantial deviations from SM Higgs production cross sections are possible. We compare the effects of fermionic operators with those associated with purely bosonic operators that have been previously discussed in the literature.https://resolver.caltech.edu/CaltechAUTHORS:KILprd07Pion leptonic decays and supersymmetry
https://resolver.caltech.edu/CaltechAUTHORS:RAMprd07
Year: 2007
DOI: 10.1103/PhysRevD.76.095017
We compute supersymmetric contributions to pion leptonic (pil2) decays in the minimal supersymmetric standard model (MSSM). When R-parity is conserved, the largest contributions to the ratio Re/µ[equivalent]Gamma[pi+-->e+nue(gamma)]/Gamma[pi+-->µ+nuµ(gamma)] arise from one-loop (V-A)[direct-product](V-A) corrections. These contributions can be potentially as large as the sensitivities of upcoming experiments; if measured, they would imply significant bounds on the chargino and slepton sectors complementary to current collider limits. We also analyze R-parity-violating interactions, which may produce a detectable deviation in Re/µ while remaining consistent with all other precision observables.https://resolver.caltech.edu/CaltechAUTHORS:RAMprd07CERN LHC phenomenology of an extended standard model with a real scalar singlet
https://resolver.caltech.edu/CaltechAUTHORS:BARprd08
Year: 2008
DOI: 10.1103/PhysRevD.77.035005
Gauge singlet extensions of the standard model (SM) scalar sector may help remedy its theoretical and phenomenological shortcomings while solving outstanding problems in cosmology. Depending on the symmetries of the scalar potential, such extensions may provide a viable candidate for the observed relic density of cold dark matter or a strong first order electroweak phase transition needed for electroweak baryogenesis. Using the simplest extension of the SM scalar sector with one real singlet field, we analyze the generic implications of a singlet-extended scalar sector for Higgs boson phenomenology at the Large Hadron Collider (LHC). We consider two broad scenarios: one in which the neutral SM Higgs and singlet mix and the other in which no mixing occurs and the singlet can be a dark matter particle. For the first scenario, we analyze constraints from electroweak precision observables and their implications for LHC Higgs phenomenology. For models in which the singlet is stable, we determine the conditions under which it can yield the observed relic density, compute the cross sections for direct detection in recoil experiments, and discuss the corresponding signatures at the LHC.https://resolver.caltech.edu/CaltechAUTHORS:BARprd08New physics effects in Higgs decay to tau leptons
https://resolver.caltech.edu/CaltechAUTHORS:20090722-144016557
Year: 2008
DOI: 10.1016/j.physletb.2007.12.021
We study the possible effects of TeV scale new physics (NP) on the rate for Higgs boson decays
to charged leptons, focusing on the τ^+τ^− channel which can be readily studied at the Large Hadron
collider. Using an SU(3)_C×SU(2)_L×U(1)_Y invariant effective theory valid below a NP scale , we
determine all effective operators up to dimension six that could generate appreciable contributions
to the decay rate and compute the dependence of the rate on the corresponding operator coefficients.
We bound the size of these operator coefficients based on the scale of the τ mass, naturalness considerations,
and experimental constraints on the τ anomalous magnetic moment. These considerations
imply that contributions to the decay rate, when Λ ~ TeV, could be comparable to the prediction
based on the SM Yukawa interaction. A reliable test of the Higgs mechanism for fermion mass
generation via the h → τ^+τ^− channel is possible only after such NP effects are understood and
brought under theoretical control.https://resolver.caltech.edu/CaltechAUTHORS:20090722-144016557Higgs-Higgsino-gaugino induced two loop electric dipole moments
https://resolver.caltech.edu/CaltechAUTHORS:LIYprd08
Year: 2008
DOI: 10.1103/PhysRevD.78.075009
We compute the complete set of Higgs-mediated chargino-neutralino two-loop contributions to the electric dipole moments of the electron and neutron in the minimal supersymmetric standard model (MSSM). We study the dependence of these contributions on the parameters that govern CP-violation in the MSSM gauge-gaugino-Higgs-Higgsino sector. We find that contributions mediated by the exchange of WH± and ZA0 pairs, where H± and A0 are the charged and CP-odd Higgs scalars, respectively, are comparable to or dominate over those mediated by the exchange of neutral gauge bosons and CP-even Higgs scalars. We also emphasize that the result of this complete set of diagrams is essential for the full quantitative study of a number of phenomenological issues, such as electric dipole moment searches and their implications for electroweak baryogenesis.https://resolver.caltech.edu/CaltechAUTHORS:LIYprd08Complex singlet extension of the standard model
https://resolver.caltech.edu/CaltechAUTHORS:BARprd09
Year: 2009
DOI: 10.1103/PhysRevD.79.015018
We analyze a simple extension of the standard model (SM) obtained by adding a complex singlet to the scalar sector (cxSM). We show that the cxSM can contain one or two viable cold dark matter candidates and analyze the conditions on the parameters of the scalar potential that yield the observed relic density. When the cxSM potential contains a global U(1) symmetry that is both softly and spontaneously broken, it contains both a viable dark matter candidate and the ingredients necessary for a strong first order electroweak phase transition as needed for electroweak baryogenesis. We also study the implications of the model for discovery of a Higgs boson at the Large Hadron Collider.https://resolver.caltech.edu/CaltechAUTHORS:BARprd09Yukawa interactions and supersymmetric electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20090817-104331688
Year: 2009
DOI: 10.1103/PhysRevLett.102.061301
We analyze the quantum transport equations for supersymmetric electroweak baryogenesis including
previously neglected bottom and tau Yukawa interactions and show that they imply the presence of a
previously unrecognized dependence of the cosmic baryon asymmetry on the spectrum of third generation
quark and lepton superpartners. For fixed values of the CP-violating phases in the supersymmetric theory,
the baryon asymmetry can vary in both magnitude and sign as a result of the squark and slepton mass
dependence. For light, right-handed top and bottom quark superpartners, the baryon number creation can
be driven primarily by interactions involving third generation leptons and their superpartners.https://resolver.caltech.edu/CaltechAUTHORS:20090817-104331688Triplet scalars and dark matter at the LHC
https://resolver.caltech.edu/CaltechAUTHORS:20090528-095827852
Year: 2009
DOI: 10.1103/PhysRevD.79.055024
We investigate the predictions of a simple extension of the standard model where the Higgs sector is composed of one SU(2)L doublet and one real triplet. We discuss the general features of the model, including its vacuum structure, theoretical and phenomenological constraints, and expectations for Higgs collider studies. The model predicts the existence of a pair of light charged scalars and, for vanishing triplet vacuum expectation value, contains a cold dark matter candidate. When the latter possibility occurs, the charged scalars are long-lived, leading to a prediction of distinctive single charged track with missing transverse energy or double charged track events at the large hadron collider. The model predicts a significant excess of two-photon events compared to SM expectations due to the presence of a light charged scalar.https://resolver.caltech.edu/CaltechAUTHORS:20090528-095827852Bino-driven electroweak baryogenesis with highly suppressed electric dipole moments
https://resolver.caltech.edu/CaltechAUTHORS:20090624-111707631
Year: 2009
DOI: 10.1016/j.physletb.2009.02.004
It is conventional wisdom that successful electroweak baryogenesis in the Minimal Supersymmetric extension of the Standard Model (MSSM) is in tension with the non-observation of electric dipole moments (EDMs), since the level of CP-violation responsible for electroweak baryogenesis is believed to generate unavoidably large EDMs. We show that CP-violation in the bino–Higgsino sector of the MSSM can account for successful electroweak baryogenesis without inducing large EDMs. This observation weakens the correlation between electroweak baryogenesis and EDMs, and makes the bino-driven electroweak baryogenesis scenario the least constrained by EDM limits. Taking this observation together with the requirement of a strongly first-order electroweak phase transition, we argue that a bino-driven scenario with a light stop is the most phenomenologically viable MSSM electroweak baryogenesis scenario.https://resolver.caltech.edu/CaltechAUTHORS:20090624-111707631Dark-matter-induced violation of the weak equivalence principle
https://resolver.caltech.edu/CaltechAUTHORS:20090807-114119837
Year: 2009
DOI: 10.1103/PhysRevLett.103.011301
A long-range fifth force coupled to dark matter can induce a coupling to ordinary matter if the dark matter interacts with standard model fields. We consider constraints on such a scenario from both astrophysical observations and laboratory experiments. We also examine the case where the dark matter is a weakly interacting massive particle, and derive relations between the coupling to dark matter and the coupling to ordinary matter for different models. Currently, this scenario is most tightly constrained by galactic dynamics, but improvements in Eötvös experiments can probe unconstrained regions of parameter space.https://resolver.caltech.edu/CaltechAUTHORS:20090807-114119837Leptoquarks and neutrino masses at the LHC
https://resolver.caltech.edu/CaltechAUTHORS:20090917-084726022
Year: 2009
DOI: 10.1016/j.nuclphysb.2009.04.009
The properties of light leptoquarks predicted in the context of a simple grand unified theory and their observability at the LHC are investigated. The SU(5) symmetry of the theory implies that the leptoquark couplings to matter are related to the neutrino mass matrix. We study the resulting connection between neutrino masses and mixing parameters and the leptoquark decays, and show that different light neutrino hierarchies imply distinctive leptoquark decay signatures. We also discuss low-energy constraints implied by searches for charged lepton flavour violation, studies of meson decays, and electroweak precision data. We perform a detailed parton-level study of the leptoquark signals and the Standard Model backgrounds at the LHC. With the clean final states containing a di-lepton plus two jets, the QCD production of the leptoquark pair can be observed for a leptoquark mass of one TeV and beyond. By examining the lepton flavor structure of the observed events, one could further test the model predictions related to the neutrino mass spectrum. In particular, b-flavor tagging will be useful in distinguishing the neutrino mass pattern and possibly probing an unknown Majorana phase in the Inverted Hierarchy or the Quasi-Degenerate scenario. Electroweak associated production of the leptoquark doublet can also be useful in identifying the quantum numbers of the leptoquarks and distinguishing between the neutrino mass spectra, even though the corresponding event rates are smaller than for QCD production. We find that with only the clean channel of μ+E/_T+jets, one could expect an observable signal for a leptoquark masses of about 600 GeV or higher.https://resolver.caltech.edu/CaltechAUTHORS:20090917-084726022Supergauge interactions and electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20100208-140431214
Year: 2009
DOI: 10.1088/1126-6708/2009/12/067
We present a complete treatment of the diffusion processes for supersymmetric electroweak baryogenesis that characterizes transport dynamics ahead of the phase transition bubble wall within the symmetric phase. In particular, we generalize existing approaches to distinguish between chemical potentials of particles and their superpartners. This allows us to test the assumption of superequilibrium (equal chemical potentials for particles and sparticles) that has usually been made in earlier studies. We show that in the Minimal Supersymmetric Standard Model, superequilibrium is generically maintained — even in the absence of fast supergauge interactions — due to the presence of Yukawa interactions. We provide both analytic arguments as well as illustrative numerical examples. We also extend the latter to regions where analytical approximations are not available since down-type Yukawa couplings or supergauge interactions only incompletely equilibrate. We further comment on cases of broken superequilibrium wherein a heavy superpartner decouples from the electroweak plasma, causing a kinematic bottleneck in the chain of equilibrating reactions. Such situations may be relevant for baryogenesis within extensions of the MSSM. We also provide a compendium of inputs required to characterize the symmetric phase transport dynamics.https://resolver.caltech.edu/CaltechAUTHORS:20100208-140431214Neutrons and the new Standard Model
https://resolver.caltech.edu/CaltechAUTHORS:20100122-082248946
Year: 2009
DOI: 10.1016/j.nima.2009.07.043
Fundamental symmetry tests with neutrons can provide unique information about whatever will be the
new Standard Model of fundamental interactions. I review two aspects of this possibility: searches for
the permanent electric dipole moment of the neutron and its relation to the origin of baryonic matter,
and precision studies of neutron decay that can probe new symmetries. I discuss the complementarity
of these experiments with other low-energy precision tests and high energy collider searches for new
physics.https://resolver.caltech.edu/CaltechAUTHORS:20100122-082248946Vacuum stability, perturbativity, and scalar singlet dark matter
https://resolver.caltech.edu/CaltechAUTHORS:20100216-132202638
Year: 2010
DOI: 10.1007/JHEP01(2010)053
We analyze the one-loop vacuum stability and perturbativity bounds on a singlet extension of the Standard Model (SM) scalar sector containing a scalar dark matter candidate. We show that the presence of the singlet-doublet quartic interaction relaxes the vacuum stability lower bound on the SM Higgs mass as a function of the cutoff and lowers the corresponding upper bound based on perturbativity considerations. We also find that vacuum stability requirements may place a lower bound on the singlet dark matter mass for given singlet quartic self coupling, leading to restrictions on the parameter space consistent with the observed relic density. We argue that discovery of a light singlet scalar dark matter particle could provide indirect information on the singlet quartic self-coupling.https://resolver.caltech.edu/CaltechAUTHORS:20100216-132202638MSSM baryogenesis and electric dipole moments: an update on the phenomenology
https://resolver.caltech.edu/CaltechAUTHORS:20100128-151617562
Year: 2010
DOI: 10.1007/JHEP01(2010)002
We explore the implications of electroweak baryogenesis for future searches for permanent electric dipole moments in the context of the minimal supersymmetric extension of the Standard Model (MSSM). From a cosmological standpoint, we point out that regions of parameter space that over-produce relic lightest supersymmetric particles can be salvaged only by assuming a dilution of the particle relic density that makes it compatible with the dark matter density: this dilution must occur after dark matter freeze-out, which ordinarily takes place after electroweak baryogenesis, implying the same degree of dilution for the generated baryon number density as well. We expand on previous studies on the viable MSSM regions for baryogenesis, exploring for the first time an orthogonal slice of the relevant parameter space, namely the (tan β, m_A) plane, and the case of non-universal relative gaugino-higgsino CP violating phases. The main result of our study is that in all cases lower limits on the size of the electric dipole moments exist, and are typically on the same order, or above, the expected sensitivity of the next generation of experimental searches, implying that MSSM electroweak baryogenesis will be soon conclusively tested.https://resolver.caltech.edu/CaltechAUTHORS:20100128-151617562Lepton-mediated electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20100517-094313019
Year: 2010
DOI: 10.1103/PhysRevD.81.063506
We investigate the impact of the tau and bottom Yukawa couplings on the transport dynamics for electroweak baryogenesis in supersymmetric extensions of the standard model. Although it has generally been assumed in the literature that all Yukawa interactions except those involving the top quark are negligible, we find that the tau and bottom Yukawa interaction rates are too fast to be neglected. We identify an illustrative "lepton-mediated electroweak baryogenesis" scenario in which the baryon asymmetry is induced mainly through the presence of a left-handed leptonic charge. We derive analytic formulas for the computation of the baryon asymmetry that, in light of these effects, are qualitatively different from those in the established literature. In this scenario, for fixed CP-violating phases, the baryon asymmetry has opposite sign compared to that calculated using established formulas.https://resolver.caltech.edu/CaltechAUTHORS:20100517-094313019Implications of a scalar dark force for terrestrial experiments
https://resolver.caltech.edu/CaltechAUTHORS:20100520-140754035
Year: 2010
DOI: 10.1103/PhysRevD.81.063507
A long-range intergalactic force between dark matter (DM) particles, mediated by an ultralight scalar, is tightly constrained by galactic dynamics and large scale structure formation. We examine the implications of such a ''dark force" for several terrestrial experiments, including Eötvös tests of the Weak Equivalence Principle (WEP), direct-detection DM searches, and collider studies. The presence of a dark force implies a nonvanishing effect in Eötvös tests that could be probed by current and future experiments depending on the DM model. For scalar DM that is a singlet under the standard model gauge groups, a dark force of astrophysically relevant magnitude is ruled out in large regions of parameter space by the DM relic density and WEP constraints. WEP tests also imply constraints on the Higgs-exchange contributions to the spin-independent (SI) DM-nucleus direct-detection cross section. For WIMP scenarios, these considerations constrain Higgs-exchange contributions to the SI cross section to be subleading compared to gauge-boson mediated contributions. In multicomponent DM scenarios, a dark force would preclude large shifts in the rate for Higgs decay to two photons associated with DM-multiplet loops that might otherwise lead to measurable deviations at the LHC or a future linear collider. The combination of observations from galactic dynamics, large scale structure formation, Eötvös experiments, DM-direct-detection experiments, and colliders can further constrain the size of new long-range forces in the dark sector.https://resolver.caltech.edu/CaltechAUTHORS:20100520-140754035Flavored quantum Boltzmann equations
https://resolver.caltech.edu/CaltechAUTHORS:20100625-082809064
Year: 2010
DOI: 10.1103/PhysRevD.81.103503
We derive from first principles, using nonequilibrium field theory, the quantum Boltzmann equations that describe the dynamics of flavor oscillations, collisions, and a time-dependent mass matrix in the early universe. Working to leading nontrivial order in ratios of relevant time scales, we study in detail a toy model for weak-scale baryogenesis: two scalar species that mix through a slowly varying time-dependent and CP-violating mass matrix, and interact with a thermal bath. This model clearly illustrates how the CP asymmetry arises through coherent flavor oscillations in a nontrivial background. We solve the Boltzmann equations numerically for the density matrices, investigating the impact of collisions in various regimes.https://resolver.caltech.edu/CaltechAUTHORS:20100625-082809064A comprehensive analysis of electric dipole moment constraints on CP-violating phases in the MSSM
https://resolver.caltech.edu/CaltechAUTHORS:20101109-082951003
Year: 2010
DOI: 10.1007/JHEP08(2010)062
We analyze the constraints placed on individual CP-violating phases in the minimal supersymmetric extension of the Standard Model (MSSM) by current experimental bounds on the electric dipole moments (EDMs) of the neutron, Thallium, and Mercury atoms. We identify the four CP-violating phases that are individually highly constrained by current EDM bounds, and we explore how these phases and correlations among them are constrained by current EDM limits. We also analyze the prospective implications of the next generation of EDM experiments. We point out that all other CP-violating phases in the MSSM are not nearly as tightly constrained by limits on the size of EDMs. We emphasize that a rich set of phenomenological consequences is potentially associated with these generically large EDM-allowed phases, ranging from B physics, electroweak baryogenesis, and signals of CP-violation at the CERN Large Hadron Collider and at future linear colliders. Our numerical study takes into account the complete set of contributions from one-and two-loop EDMs of the electron and quarks, one-and two-loop Chromo-EDMs of quarks, the Weinberg 3-gluon operator, and dominant 4-fermion CP-odd operator contributions, including contributions which are both included and not included yet in the CPsuperH2.0 package. We also introduce an open-source numerical package, 2LEDM, which provides the complete set of two-loop electroweak diagrams contributing to the electric dipole moments of leptons and quarks.https://resolver.caltech.edu/CaltechAUTHORS:20101109-082951003Electron-to-tau lepton flavor violation at the Electron-Ion Collider
https://resolver.caltech.edu/CaltechAUTHORS:20110103-144453739
Year: 2010
DOI: 10.1007/JHEP11(2010)045
We analyze the potential sensitivity of a search for e → τ conversion at a proposed electron-ion collider (EIC) facility. To that end, we calculate the cross sections for e → τ events in a leptoquark framework assuming that the leptoquark masses are on the order of several hundred GeV or more. Given present limits on leptoquarks from direct searches at HERA and rare decay processes, an EIC sensitive to 0.1 fb e → τ cross sections could probe previously unexplored regions of parameter space for these lepton flavor violating events (assuming 90 GeV center-of-mass energy and 10 fb^(−1) integrated luminosity). Depending on the species of leptoquark and flavor structure of the couplings, an EIC search could surpass the HERA and rare process sensitivity to e → τ conversion amplitudes by as much as an order of magnitude or more. We also derive updated limits on quark flavor-diagonal LFV leptoquark interactions using the most recent BaBar τ → eγ search. We find that limits from an EIC e → τ search could be competitive with the most recent τ → eγ limit for a subset of the quark flavor-diagonal leptoquark couplings. Using an SU(5) GUT model in which leptoquark couplings are constrained by theneutrino masses and mixing, we illustrate how observable leptoquark-induced e → τ conversion can be consistent with stringent LFV limits imposed by → eγ and e conversion searches.https://resolver.caltech.edu/CaltechAUTHORS:20110103-144453739Examination of higher-order twist contributions in parity-violating deep-inelastic electron-deuteron scattering
https://resolver.caltech.edu/CaltechAUTHORS:20110317-102027897
Year: 2010
DOI: 10.1103/PhysRevC.82.065205
We show that parity-violating deep-inelastic scattering (PVDIS) of longitudinally polarized electrons from deuterium can in principle be a
relatively clean probe of higher twist quark-quark correlations beyond
the parton model. As first observed by Bjorken and Wolfenstein, the
dominant contribution to the electron polarization asymmetry,
proportional to the axial vector electron coupling, receives
corrections at twist four from the matrix element of a single
four-quark operator. We reformulate the Bjorken-Wolfenstein argument in
a matter suitable for the interpretation of experiments planned at the
Thomas Jefferson National Accelerator Facility (JLab). In particular,
we observe that because the contribution of the relevant twist-four
operator satisfies the Callan-Gross relation, the ratio of
parity-violating longitudinal and transverse cross sections, R^(γZ),
is identical to that for purely electromagnetic scattering, R^γ, up
to perturbative and power-suppressed contributions. This result
simplifies the interpretation of the asymmetry in terms of other
possible novel hadronic and electroweak contributions. We use the
results of MIT Bag Model calculations to estimate contributions of the
relevant twist-four operator to the leading term in the asymmetry as a
function of Bjorken x and Q^2. We compare these estimates with
possible leading twist corrections from violation of charge symmetry in
the parton distribution functions.https://resolver.caltech.edu/CaltechAUTHORS:20110317-102027897Baryon washout, electroweak phase transition, and perturbation theory
https://resolver.caltech.edu/CaltechAUTHORS:20111011-120143714
Year: 2011
DOI: 10.1007/JHEP07(2011)029
We analyze the conventional perturbative treatment of sphaleron-induced baryon number washout relevant for electroweak baryogenesis and show that it is not gauge independent due to the failure of consistently implementing the Nielsen identities order-by order in perturbation theory. We provide a gauge-independent criterion for baryon number preservation in place of the conventional (gauge-dependent) criterion needed for successful electroweak baryogenesis. We also review the arguments leading to the preservation criterion and analyze several sources of theoretical uncertainties in obtaining a numerical bound. In various beyond the standard model scenarios, a realistic perturbative treatment will likely require knowledge of the complete two-loop finite temperature effective potential
and the one-loop sphaleron rate.https://resolver.caltech.edu/CaltechAUTHORS:20111011-120143714Model dependence of the γ Z dispersion correction to the parity-violating asymmetry in elastic ep scattering
https://resolver.caltech.edu/CaltechAUTHORS:20110812-154710243
Year: 2011
DOI: 10.1103/PhysRevC.84.015502
We analyze the dispersion correction to elastic parity violating electron-proton scattering due to γZ exchange. In particular, we explore the theoretical uncertainties associated with modeling contributions of hadronic intermediate states. Taking into account constraints from low- and high-energy, parity-conserving electroproduction measurements, choosing different models for contributions from the nonresonant processes, and performing the corresponding flavor rotations to obtain the electroweak amplitude, we arrive at an estimate of the uncertainty in the total contribution to the parity-violating asymmetry. At the kinematics of the Q-Weak experiment, we obtain a correction to the asymmetry equivalent to a shift in the proton weak charge of (0.0054±0.0020). This should be compared to the value of the proton's weak charge of QW^p=0.0713±0.0008 that includes Standard Model contributions at tree level and one-loop radiative corrections. Therefore, we obtain a new Standard Model prediction for the parity-violating asymmetry in the kinematics of the Q-Weak experiment of (0.0767±0.0008±0.0020_(γZ)). The latter error leads to a relative uncertainty of 2.8% in the determination of the proton's weak charge and is dominated by the uncertainty in the isospin structure of the inclusive cross section. We argue that future parity-violating inelastic ep asymmetry measurements at low to moderate Q^2 and W^2 could be exploited to reduce the uncertainty associated with the dispersion correction. Because the corresponding shift and error bar decrease monotonically with decreasing beam energy, a determination of the proton's weak charge with a lower-energy experiment or measurements of "isotope ratios" in atomic parity violation could provide a useful cross-check on any implications for physics beyond the Standard Model derived from the Q-Weak measurement.https://resolver.caltech.edu/CaltechAUTHORS:20110812-154710243Diagnosing spin at the LHC via vector boson fusion
https://resolver.caltech.edu/CaltechAUTHORS:20111216-163100532
Year: 2011
DOI: 10.1007/JHEP09(2011)094
We propose a new technique for determining the spin of new massive particles that might be discovered at the Large Hadron Collider. The method relies on pair-production of the new particles in a kinematic regime where the vector boson fusion production of color singlets is enhanced. For this regime, we show that the distribution of the leading jets as a function of their relative azimuthal angle can be used to distinguish spin-0 from spin-½ particles. We illustrate this effect by considering the particular cases of (i) strongly-interacting, stable particles and (ii) supersymmetric particles carrying color charge. We argue that this method should be applicable in a wide range of new physics scenarios.https://resolver.caltech.edu/CaltechAUTHORS:20111216-163100532RvMDM and lepton flavor violation
https://resolver.caltech.edu/CaltechAUTHORS:20120326-091011513
Year: 2011
DOI: 10.1007/JHEP12(2011)054
A model relating radiative seesaw and minimal dark matter mass scales without beyond the standard model (SM) gauge symmetry (RνMDM) is constructed. In addition to the SM particles, the RνMDM contains, a Majorana fermion multiplet N _R and scalar multiplet χ that transform respectively as (1, 5, 0) and (1,6,−1/2) under the SM gauge group SU(3)_C × SU(2) _L × U(1)_Y . The neutral component N_R^0 plays the role of dark matter with a mass in the range of 9 to 10 TeV. This scale also sets the lower limit for the scale for the heavy degrees of freedom in N_R and χ which generate light neutrino masses through the radiative seesaw mechanism. The model predicts an N_R^0-nucleus scattering cross section that would be accessible with future dark matter direct detection searches as well as observable effects in present and searches for charged lepton flavor violating processes, such as l_i → l_j γ and μ − e conversion.https://resolver.caltech.edu/CaltechAUTHORS:20120326-091011513Electroweak Beautygenesis: From b → s CP Violation to the Cosmic Baryon Asymmetry
https://resolver.caltech.edu/CaltechAUTHORS:20120625-163639080
Year: 2012
DOI: 10.1103/PhysRevLett.108.221301
We address the possibility that CP violation in B_s-B̅_s mixing may help explain the origin of the cosmic
baryon asymmetry. We propose a new baryogenesis mechanism—"electroweak beautygenesis"—explicitly
showing that these two CP-violating phenomena can be sourced by a common CP phase. As an
illustration, we work in the two-Higgs-doublet model. Because the relevant CP phase is flavor off
diagonal, this mechanism is less severely constrained by null results of electric dipole moment searches
than other scenarios. We show how measurements of flavor observables by the D0, CDF, and LHCb
collaborations test this scenario.https://resolver.caltech.edu/CaltechAUTHORS:20120625-163639080Precision probes of a leptophobic Z' boson
https://resolver.caltech.edu/CaltechAUTHORS:20120710-105017177
Year: 2012
DOI: 10.1016/j.physletb.2012.04.077
Extensions of the Standard Model that contain leptophobic Z' gauge bosons are theoretically interesting but difficult to probe directly in high-energy hadron colliders. However, precision measurements of Standard Model neutral current processes can provide powerful indirect tests. We demonstrate that parity-violating deep inelastic scattering of polarized electrons off of deuterium offer a unique probeleptophobic Z' bosons with axial quark couplings and masses above 100 GeV. In addition to covering a wide range of previously uncharted parameter space, planned measurements of the deep inelastic parity-violating eD asymmetry would be capable of testing leptophobic Z' scenarios proposed to explain the CDF W plus dijet anomaly.https://resolver.caltech.edu/CaltechAUTHORS:20120710-105017177Complex scalar singlet dark matter: Vacuum stability and phenomenology
https://resolver.caltech.edu/CaltechAUTHORS:20120907-090818088
Year: 2012
DOI: 10.1103/PhysRevD.86.043511
We analyze one-loop vacuum stability, perturbativity, and phenomenological constraints on a complex singlet extension of the standard model scalar sector containing a scalar dark matter candidate. We study vacuum stability considerations using a gauge-invariant approach and compare with the conventional gauge-dependent procedure. We show that, if new physics exists at the TeV scale, the vacuum stability analysis and experimental constraints from the dark matter sector, electroweak precision data, and LEP allow both a Higgs-like scalar in the mass range allowed by the latest results from CMS and ATLAS and a lighter singlet-like scalar with weak couplings to standard model particles. If instead no new physics appears until higher energy scales, there may be significant tension between the vacuum stability analysis and phenomenological constraints (in particular electroweak precision data) to the extent that the complex singlet extension with light Higgs and singlet masses would be ruled out. We comment on the possible implications of a scalar with ∼125 GeV mass and future ATLAS invisible decay searches.https://resolver.caltech.edu/CaltechAUTHORS:20120907-090818088Hadronic light-by-light scattering and the pion polarizability
https://resolver.caltech.edu/CaltechAUTHORS:20121008-143319217
Year: 2012
DOI: 10.1103/PhysRevD.86.037502
We compute the charged pion loop contribution to the light-by-light scattering amplitude for off-shell photons in chiral perturbation theory through next-to-leading order (NLO). We show that for small photon virtualities (k^2≪m^(2)_(π)) the NLO contributions are relatively more important due to an accidental numerical suppression of the LO terms. This behavior is consistent with previous calculations of the hadronic light-by-light contribution to the muon anomalous magnetic moment, a^(HLBL)_(μ), whose leading order value receives O(1) corrections from models incorporating some of the NLO physics. We also show that models employed thus far for the charged pion loop contribution to a^(HLBL)_(μ) are not fully consistent with low-momentum behavior implied by quantum chromodynamics, having omitted potentially significant contributions from the pion polarizability.https://resolver.caltech.edu/CaltechAUTHORS:20121008-143319217Phase transitions and gauge artifacts in an Abelian Higgs boson plus singlet model
https://resolver.caltech.edu/CaltechAUTHORS:20121206-100620805
Year: 2012
DOI: 10.1103/PhysRevD.86.083537
While the finite-temperature effective potential in a gauge theory is a gauge-dependent quantity, in several instances a first-order phase transition can be triggered by gauge-independent terms. A particularly interesting case occurs when the potential barrier separating the broken and symmetric vacua of a spontaneously broken symmetry is produced by tree-level terms in the potential. Here, we study this scenario in a simple Abelian Higgs model, for which the gauge-invariant potential is known, augmented with a singlet real scalar. We analyze the possible symmetry-breaking patterns in the model, and illustrate in which cases gauge artifacts are expected to manifest themselves most severely. We then show that gauge artifacts can be pronounced even in the presence of a relatively large, tree-level singlet-Higgs cubic interaction. When the transition is strongly first order, these artifacts, while present, are more subtle than in the generic situation.https://resolver.caltech.edu/CaltechAUTHORS:20121206-100620805Supersymmetric electroweak baryogenesis via resonant sfermion sources
https://resolver.caltech.edu/CaltechAUTHORS:20130107-101716261
Year: 2012
DOI: 10.1103/PhysRevD.86.096001
We calculate the baryon asymmetry produced at the electroweak phase transition by quasidegenerate third-generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large tanβ, where third-generation down-type (s)fermions become relevant. We show that in the case of top squark and sbottom sources, the viable parameter space is ruled out by constraints from the nonobservation of the Mercury electric dipole moment. We introduce a new class of CP-violating sources, quasidegenerate staus, that escapes current electric dipole moment constraints while providing large enough net chiral currents to achieve successful slepton-mediated electroweak baryogenesis.https://resolver.caltech.edu/CaltechAUTHORS:20130107-101716261Electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20130103-135329572
Year: 2012
DOI: 10.1088/1367-2630/14/12/125003
Electroweak baryogenesis (EWBG) remains a theoretically attractive and experimentally testable scenario for explaining the cosmic baryon asymmetry. We review recent progress in computations of the baryon asymmetry within this framework and discuss their phenomenological consequences. We pay particular attention to methods for analyzing the electroweak phase transition and calculating CP-violating asymmetries, the development of Standard Model extensions that may provide the necessary ingredients for EWBG, and searches for corresponding signatures at the high energy, intensity and cosmological frontiers.https://resolver.caltech.edu/CaltechAUTHORS:20130103-135329572Higgs vacuum stability, neutrino mass, and dark matter
https://resolver.caltech.edu/CaltechAUTHORS:20130125-102827986
Year: 2012
DOI: 10.1103/PhysRevD.86.113017
Recent results from ATLAS and CMS point to a narrow range for the Higgs mass: M_H∈(124,126) GeV. Given this range, a case may be made for new physics beyond the Standard Model (SM) because of the resultant vacuum stability problem, i.e., the SM Higgs quartic coupling may run to negative values at a scale below the Planck scale. We study representative minimal extensions of the SM that can keep the SM Higgs vacuum stable to the Planck scale by introducing new scalar or fermion interactions at the TeV scale while solving other phenomenological problems. In particular, we consider the type-II seesaw model, which is introduced to explain the nonzero Majorana masses of the active neutrinos. Similarly, we observe that if the stability of the SM Higgs vacuum is ensured by the running of the gauge sector couplings, then one may require a series of new electroweak multiplets, the neutral component of which can be a cold dark matter candidate. Stability may also point to a new U(1) gauge symmetry, in which the SM Higgs carries a nonzero charge.https://resolver.caltech.edu/CaltechAUTHORS:20130125-102827986Electric dipole moment of the ρ meson
https://resolver.caltech.edu/CaltechAUTHORS:20130305-081831809
Year: 2013
DOI: 10.1103/PhysRevC.87.015205
At a hadronic scale the effect of CP-violating interactions that typically appear in extensions of the Standard Model may be described by an effective Lagrangian, in which the operators are expressed in terms of lepton and partonic gluon and quark fields and ordered by their mass dimension, k⩾4. Using a global-symmetry-preserving truncation of QCD Dyson-Schwinger equations, we compute the ρ-meson's electric dipole moment (EDM), d_ρ, as generated by the leading dimension-four and dimension-five CP-violating operators and an example of a dimension-six four-quark operator. The two dimension-five operators, i.e., the quark EDM and quark chromo-EDM, produce contributions to d_ρ whose coefficients are of the same sign and within a factor of 2 in magnitude. Moreover, should a suppression mechanism be verified for the θ term in any beyond-Standard-Model theory, the contribution from a four-quark operator can match the quark EDM and quark chromo-EDM in importance. This study serves as a prototype for the more challenging task of computing the neutron's EDM.https://resolver.caltech.edu/CaltechAUTHORS:20130305-081831809Leptophobic Z′ boson and parity-violating eD scattering
https://resolver.caltech.edu/CaltechAUTHORS:20130424-104835448
Year: 2013
DOI: 10.1103/PhysRevD.87.055013
We study the impact of a leptophobic Z′ gauge boson on the C1q and C2q parameters that describe the low-energy, parity-violating electron-quark neutral current interaction. We complement previous work by including the penguin-like vertex corrections, thereby completing the analysis of one-loop calculation up to O(m^(2)_(q′)/M^(2)_(Z′)) terms. We analyze the sensitivity of these probes to the different couplings Z′u̅ q (q=u, c, t) and Z′d̅ q (q=d, s, b) in a model-independent way that can be applied to any specific Z′ scenario. We show that constraints from neutral kaon and heavy flavor studies preclude significant contributions from flavor nondiagonal couplings except for those involving top quarks. We apply our results to a light Z′ with flavor diagonal couplings to up or down quarks, a scenario proposed in the literature to explain the CDF W plus dijet anomaly. We find that such a particle would not affect the C_1q coefficients, but it would have a sizable impact on C_2q couplings that can be probed by future measurements of parity-violating deep inelastic scattering of polarized electrons off of deuterium.https://resolver.caltech.edu/CaltechAUTHORS:20130424-104835448Electric dipole moments of nucleons, nuclei, and atoms: The Standard Model and beyond
https://resolver.caltech.edu/CaltechAUTHORS:20130809-084130584
Year: 2013
DOI: 10.1016/j.ppnp.2013.03.003
Searches for the permanent electric dipole moments (EDMs) of molecules, atoms, nucleons and nuclei provide powerful probes of CP violation both within the Standard Model and beyond the Standard Model (BSM). The interpretation of experimental EDM limits requires careful delineation of physics at a wide range of scales, from the long-range atomic and molecular scales to the short-distance dynamics of physics at or beyond the Fermi scale. In this review, we provide a framework for disentangling contributions from physics at these disparate scales, building out from the set of dimension four and six effective operators that embody CP violation at the Fermi scale. We survey computations of hadronic and nuclear matrix elements associated with Fermi-scale CP violation in systems of experimental interest and quantify the present level of theoretical uncertainty in these calculations. Using representative BSM scenarios of current interest, we discuss ways in which the interplay of physics at various scales can generate EDMs at a potentially observable level.https://resolver.caltech.edu/CaltechAUTHORS:20130809-084130584Low energy probes of physics beyond the standard model
https://resolver.caltech.edu/CaltechAUTHORS:20130809-083813693
Year: 2013
DOI: 10.1016/j.ppnp.2013.03.002
Low-energy tests of fundamental symmetries and studies of neutrino properties provide a powerful window on physics beyond the Standard Model (BSM). In this article, we provide a basic theoretical framework for a subsequent set of articles that review the progress and opportunities in various aspects of the low-energy program. We illustrate the physics reach of different low-energy probes in terms of an effective BSM mass scale and illustrate how this reach matches and, in some cases, even exceeds that accessible at the high energy frontier.https://resolver.caltech.edu/CaltechAUTHORS:20130809-083813693Color breaking in the early universe
https://resolver.caltech.edu/CaltechAUTHORS:20130812-151057238
Year: 2013
DOI: 10.1103/PhysRevD.88.015003
We explore the possibility that SU(3)_C was not an exact symmetry at all times in the early Universe, using minimal extensions of the standard model that contain a color triplet scalar field and perhaps other fields. We show that, for a range of temperatures, there can exist a phase in which the free energy is minimized when the color triplet scalar has a nonvanishing vacuum expectation value, spontaneously breaking color. At very high temperatures and at lower temperatures, color symmetry is restored. The breaking of color in this phase is accompanied by the spontaneous breaking of B - L if the color triplet scalar Yukawa couples to quarks and/or leptons. We discuss the requirements on the minimal extensions needed for consistency of this scenario with present collider bounds on new colored scalar particles.https://resolver.caltech.edu/CaltechAUTHORS:20130812-151057238Parity-violating deep-inelastic electron-deuteron scattering: Higher twist and parton angular momentum
https://resolver.caltech.edu/CaltechAUTHORS:20130809-143149259
Year: 2013
DOI: 10.1103/PhysRevC.88.015202
We study the effect of parton angular momentum on the twist-four correction to the left-right asymmetry in the electron-deuteron parity-violating deep-inelastic scattering (PVDIS). We show that this higher-twist correction is transparent to the dynamics of parton angular momentum needed to account for the Sivers and Boer-Mulders functions and spin-independent parton distribution functions. A sufficiently precise measurement of the PVDIS asymmetry may, thus, provide additional information about the parton dynamics responsible for nucleon spin.https://resolver.caltech.edu/CaltechAUTHORS:20130809-143149259Stepping into electroweak symmetry breaking: Phase transitions and Higgs phenomenology
https://resolver.caltech.edu/CaltechAUTHORS:20130909-110816925
Year: 2013
DOI: 10.1103/PhysRevD.88.035013
We study the dynamics of electroweak symmetry breaking in an extension of the Standard Model where the Higgs sector is augmented by the addition of a real (Y=0) isospin triplet. We show that this scenario exhibits a novel, two-step electroweak phase transition, wherein the first step provides the strongly first-order transition as required for electroweak baryogenesis, followed by a second step to the Standard Model Higgs phase that also admits a cold dark matter candidate. We analyze the constraints on this scenario from recent results obtained at the Large Hadron Collider for the Higgs diphoton decay channel. We argue that this two-step scenario can be generalized to extensions of the Standard Model with additional higher-dimensional scalar multiplets that may yield realistic baryogenesis dynamics.https://resolver.caltech.edu/CaltechAUTHORS:20130909-110816925Hidden from view: Neutrino masses, dark matter, and TeV-scale leptogenesis in a neutrinophilic two-Higgs-doublet model
https://resolver.caltech.edu/CaltechAUTHORS:20140403-092055747
Year: 2014
DOI: 10.1103/PhysRevD.89.033007
We consider a simple extension of the Standard Model providing dark matter and a TeV-scale seesaw mechanism that also allows for viable leptogenesis. In addition to the Standard Model degrees of freedom, the model contains a neutrinophilic Higgs doublet, a scalar singlet, and six singlet fermions (including three right-handed Majorana neutrinos) that are charged under a local U(1)′ gauge symmetry. We show how the U(1)′ charge assignments and the choice of scalar potential can lead to a TeV-scale seesaw mechanism and O(1) neutrino Yukawa couplings in a straightforward way. While this scenario has all the ingredients one would expect for significant experimental signatures, including several new TeV-scale degrees of freedom, we find that most distinctive features associated with neutrino mass generation, leptogenesis and the dark sector are likely to remain inaccessible in the absence of additional lepton flavor symmetries.https://resolver.caltech.edu/CaltechAUTHORS:20140403-092055747Cuts, cancellations and the closed time path: The soft leptogenesis example
https://resolver.caltech.edu/CaltechAUTHORS:20140612-142028573
Year: 2014
DOI: 10.1016/j.nuclphysb.2014.02.012
By including all leading quantum-statistical effects at finite temperature, we show that no net asymmetry of leptons and sleptons is generated from soft leptogenesis, save the possible contribution from the resonant mixing of sneutrinos. This result contrasts with different conclusions appearing in the literature that are based on an incomplete inclusion of quantum statistics. We discuss vertex and wave-function diagrams as well as all different possible kinematic cuts that nominally lead to CP-violating asymmetries. The present example of soft leptogenesis may therefore serve as a paradigm in order to identify more generally applicable caveats relevant to alternative scenarios for baryogenesis and leptogenesis, and it may provide useful guidance in constructing viable models.https://resolver.caltech.edu/CaltechAUTHORS:20140612-142028573Probing the Higgs portal at the LHC through resonant di-Higgs production
https://resolver.caltech.edu/CaltechAUTHORS:20140708-094409635
Year: 2014
DOI: 10.1103/PhysRevD.89.095031
We investigate resonant di-Higgs production as a means of probing extended scalar sectors that include a 125 GeV Standard Model-like Higgs boson. For concreteness, we consider a gauge singlet Higgs portal scenario leading to two mixed doublet-singlet states, h_(1,2). For m(_h_2)>2m(_h_1), the resonant di-Higgs production process pp→h_(2)→h_(1)h_(1) will lead to final states associated with the decaying pair of Standard Model-like Higgs scalars. We focus on h_(2) production via gluon fusion and on the bb^¯τ^(+)τ^(−) final state. We find that discovery of the h_(2) at the LHC may be achieved with ≲100 fb^(−1) of integrated luminosity for benchmark parameter choices relevant to cosmology. Our analysis directly maps onto the decoupling limit of the next-to-minimal supersymmetric Standard Model and more generically onto extensions of the Standard Model Higgs sector in which a heavy scalar produced through gluon-fusion decays to a pair of Standard Model-like Higgs bosons.https://resolver.caltech.edu/CaltechAUTHORS:20140708-094409635CP-violating phenomenology of flavor conserving two Higgs doublet models
https://resolver.caltech.edu/CaltechAUTHORS:20140807-085331165
Year: 2014
DOI: 10.1103/PhysRevD.89.115023
We analyze the constraints on CP-violating, flavor conserving two Higgs doublet models implied by measurements of Higgs boson properties at the Large Hadron Collider (LHC) and by the nonobservation of permanent electric dipole moments (EDMs) of molecules, atoms, and neutrons. We find that the LHC and EDM constraints are largely complementary, with the LHC studies constraining the mixing between the neutral CP-even states and the EDMs probing the effect of mixing between the CP-even and CP-odd scalars. Presently, the most stringent constraints are implied by the nonobservation of the ThO molecule EDM signal. Future improvements in the sensitivity of neutron and diamagnetic atom EDM searches could yield competitive or even more severe constraints. We analyze the quantitative impact of hadronic and nuclear theory uncertainties on the interpretation of the latter systems and conclude that these uncertainties cloud the impact of projected improvements in the corresponding experimental sensitivities.https://resolver.caltech.edu/CaltechAUTHORS:20140807-085331165Top squark with mass close to the top quark
https://resolver.caltech.edu/CaltechAUTHORS:20140925-085416041
Year: 2014
DOI: 10.1103/PhysRevD.90.014046
The most natural supersymmetric solution to the hierarchy problem prefers the scalar top partner to be close in mass to the top quark. Experimental searches exclude top squarks across a wide range of masses, but a gap remains when the difference between the masses of the stop and the lightest supersymmetric particle is close to the top mass. We propose to search for stops in this regime by exploiting the azimuthal angular correlation of forward tagging jets in (s)top pair production. As shown in earlier work, this correlation is sensitive to the spin of the heavy states, allowing one to distinguish between top and stop pair production. Here, we demonstrate that this angular information can give a statistically significant stop pair production signal in the upcoming LHC run. While the appropriate simulation including parton showering and detector simulation requires some care, we find stable predictions for the angular correlation using multijet merging.https://resolver.caltech.edu/CaltechAUTHORS:20140925-085416041Distinguishing axions from generic light scalars using electric dipole moment and fifth-force experiments
https://resolver.caltech.edu/CaltechAUTHORS:20141023-131016124
Year: 2014
DOI: 10.1103/PhysRevD.90.054016
We derive electric dipole moment (EDM) constraints on possible new macroscopic time-reversal and parity-violating (TVPV) spin-dependent forces. These constraints are compared to those derived from direct searches in fifth-force experiments and from combining laboratory searches with astrophysical bounds on stellar energy loss. For axion-mediated TVPV spin-dependent forces, EDM constraints dominate over fifth-force limits by several orders of magnitude. However, we show that for a generic light scalar, unrelated to the strong CP problem, present bounds from direct fifth-force searches are more stringent than those inferred from EDM limits for the interaction ranges explored by fifth-force experiments. Thus, correlating observations in EDM and fifth-force experiments could help distinguish axions from more generic light scalar scenarios.https://resolver.caltech.edu/CaltechAUTHORS:20141023-131016124Nucleon electric dipole moments and the isovector parity-and time-reversal-odd pion–nucleon coupling
https://resolver.caltech.edu/CaltechAUTHORS:20141017-082629056
Year: 2014
DOI: 10.1016/j.physletb.2014.07.014
The isovector time-reversal- and parity-violating pion–nucleon coupling g_π^(1) is uniquely sensitive to dimension-six interactions between right-handed light quarks and the Standard Model Higgs doublet that naturally arises in left-right symmetric models. Recent work has used the g_π^(1)-induced one-loop contribution to the neutron electric dipole moment d_n, together with the present experimental d_n bound, to constrain the CP-violating parameters of the left-right symmetric model. We show that this and related analyses are based on an earlier meson theory d_n computation that is not consistent with the power-counting appropriate for an effective field theory. We repeat the one-loop calculation using heavy baryon chiral perturbation theory and find that the resulting d_n sensitivity to g_π^(1) is suppressed, implying more relaxed constraints on the parameter space of the left-right symmetric model. Assuming no cancellations between this loop contribution and other contributions, such as the leading order EDM low-energy constant, the present limit on d_n implies |g_π^(1)|≲1.1×10^(−10).https://resolver.caltech.edu/CaltechAUTHORS:20141017-082629056Electroweak baryogenesis, electric dipole moments, and Higgs diphoton decays
https://resolver.caltech.edu/CaltechAUTHORS:20141211-102544879
Year: 2014
DOI: 10.1007/JHEP10(2014)180
We study the viability of electroweak baryogenesis in a two Higgs doublet model scenario augmented by vector-like, electroweakly interacting fermions. Considering a limited, but illustrative region of the model parameter space, we obtain the observed cosmic baryon asymmetry while satisfying present constraints from the non-observation of the permanent electric dipole moment (EDM) of the electron and the combined ATLAS and CMS result for the Higgs boson diphoton decay rate. The observation of a non-zero electron EDM in a next generation experiment and/or the observation of an excess (over the Standard Model) of Higgs to diphoton events with the 14 TeV LHC run or a future e^+e^− collider would be consistent with generation of the observed baryon asymmetry in this scenario.https://resolver.caltech.edu/CaltechAUTHORS:20141211-102544879The Muon Anomalous Magnetic Moment and the Pion Polarizability
https://resolver.caltech.edu/CaltechAUTHORS:20130925-142110583
Year: 2014
DOI: 10.1016/j.physletb.2014.09.006
We compute the charged pion loop contribution to the muon anomalous magnetic moment ɑ_µ, taking into account the effect of the charged pion polarizability, (ɑ_1 - β_1)_π^+. We evaluate this contribution using two different models that are consistent with the requirements of chiral symmetry in the low-momentum regime and perturbative quantum chromodynamics in the asymptotic region. The result increases the disagreement between the present experimental value for ɑ_µ and the theoretical, Standard Model prediction by as much as ~ 60 x 10^(-11), depending on the value of (ɑ_1 - β_1)_π^+ and the choice of the model. The planned determination of (ɑ_1 - β_1)_π^+ at Jefferson Laboratory will eliminate the dominant parametric error, leaving a theoretical model uncertainty commensurate with the error expected from planned Fermilab measurement of a_µ.https://resolver.caltech.edu/CaltechAUTHORS:20130925-142110583Impact of LSP character on Slepton reach at the LHC
https://resolver.caltech.edu/CaltechAUTHORS:20150108-072038224
Year: 2014
DOI: 10.1007/JHEP11(2014)117
Searches for supersymmetry at the Large Hadron Collider (LHC) have significantly constrained the parameter space associated with colored superpartners, whereas the constraints on color-singlet superpartners are considerably less severe. In this study, we investigate the dependence of slepton decay branching fractions on the nature of the lightest supersymmetric particle (LSP). In particular, in the Higgsino-like LSP scenarios, both decay branching fractions of ℓ~L and ν~ℓ depend strongly on the sign and value of M_1/M_2, which has strong implications for the reach of dilepton plus E_T searches for slepton pair production. We extend the experimental results for same flavor, opposite sign dilepton plus E_T searches at the 8TeV LHC to various LSP scenarios. We find that the LHC bounds on sleptons are strongly enhanced for a non-Bino-like LSP: the 95% C.L. limit for mℓ_L extends from 300 GeV for a Bino-like LSP to about 370 GeV for a Wino-like LSP. The bound for ℓ_L with a Higgsino-like LSP is the strongest (∼ 490 GeV) for M_1/M_2 ∼ − tan^2 θ_W and is the weakest (∼ 220 GeV) for M_1/M_2 ∼ tan^2 θ_W . We also calculate prospective slepton search reaches at the 14 TeV LHC. With 100 fb^(−1) integrated luminosity, the projected 95% C.L. mass reach for the left-handed slepton varies from 550 (670) GeV for a Bino-like (Winolike) LSP to 900 (390) GeV for a Higgsino-like LSP under the most optimistic (pessimistic) scenario. The reach for the right-handed slepton is about 440 GeV. The corresponding 5σ discovery sensitivity is about 100 GeV smaller. For 300 fb^(−1) integrated luminosity, the reach is about 50 − 100 GeV higher.https://resolver.caltech.edu/CaltechAUTHORS:20150108-072038224Singlet-catalyzed electroweak phase transitions and precision Higgs boson studies
https://resolver.caltech.edu/CaltechAUTHORS:20150501-083329551
Year: 2015
DOI: 10.1103/PhysRevD.91.035018
We update the phenomenology of gauge-singlet extensions of the Standard Model scalar sector and their implications for the electroweak phase transition. Considering the introduction of one real scalar singlet to the scalar potential, we analyze present constraints on the potential parameters from Higgs coupling measurements at the Large Hadron Collider (LHC) and electroweak precision observables for the kinematic regime in which no new scalar decay modes arise. We then show how future precision measurements of Higgs boson signal strengths and the Higgs self-coupling could probe the scalar potential parameter space associated with a strong first-order electroweak phase transition. We illustrate using benchmark precision for several future collider options, including the high-luminosity LHC, the International Linear Collider, Triple-Large Electron-Positron collider, the China Electron-Positron Collider, and a 100 TeV proton-proton collider, such as the Very High Energy LHC or the Super Proton-Proton Collider. For the regions of parameter space leading to a strong first-order electroweak phase transition, we find that there exists considerable potential for observable deviations from purely Standard Model Higgs properties at these prospective future colliders.https://resolver.caltech.edu/CaltechAUTHORS:20150501-083329551Electric dipole moments: A global analysis
https://resolver.caltech.edu/CaltechAUTHORS:20150420-102927464
Year: 2015
DOI: 10.1103/PhysRevC.91.035502
We perform a global analysis of searches for the permanent electric dipole moments (EDMs) of the neutron, neutral atoms, and molecules in terms of six leptonic, semileptonic, and nonleptonic interactions involving photons, electrons, pions, and nucleons. By translating the results into fundamental charge-conjugation-parity symmetry (CP) violating effective interactions through dimension six involving standard model particles, we obtain rough lower bounds on the scale of beyond the standard model CP-violating interactions ranging from 1.5 TeV for the electron EDM to 1300 TeV for the nuclear spin-independent electron-quark interaction. We show that planned future measurements involving systems or combinations of systems with complementary sensitivities to the low-energy parameters may extend the mass reach by an order of magnitude or more.https://resolver.caltech.edu/CaltechAUTHORS:20150420-102927464Stop-catalyzed baryogenesis beyond the MSSM
https://resolver.caltech.edu/CaltechAUTHORS:20151218-102819160
Year: 2015
DOI: 10.1103/PhysRevD.92.095019
Nonminimal supersymmetric models that predict a tree-level Higgs mass above the minimal supersymmetric standard model (MSSM) bound are well motivated by naturalness considerations. Indirect constraints on the stop sector parameters of such models are significantly relaxed compared to the MSSM; in particular, both stops can have weak-scale masses. We revisit the stop-catalyzed electroweak baryogenesis (EWB) scenario in this context. We find that the LHC measurements of the Higgs boson production and decay rates already rule out the possibility of stop-catalyzed EWB. We also introduce a gauge-invariant analysis framework that may generalize to other scenarios in which interactions outside the gauge sector drive the electroweak phase transition.https://resolver.caltech.edu/CaltechAUTHORS:20151218-102819160Two-step electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20160211-111739407
Year: 2016
DOI: 10.1103/PhysRevD.93.015013
We analyze electroweak baryogenesis during a two-step electroweak symmetry-breaking transition, wherein the baryon asymmetry is generated during the first step and preserved during the second. Focusing on the dynamics of CP violation required for asymmetry generation, we discuss general considerations for successful two-step baryogenesis. Using a concrete model realization, we illustrate in detail the viability of this scenario and the implications for present and future electric dipole moment (EDM) searches. We find that CP violation associated with a partially excluded sector may yield the observed baryon asymmetry while evading present and future EDM constraints.https://resolver.caltech.edu/CaltechAUTHORS:20160211-111739407Indirect detection imprint of a CP violating dark sector
https://resolver.caltech.edu/CaltechAUTHORS:20160601-141504526
Year: 2016
DOI: 10.1103/PhysRevD.93.095025
We introduce a simple scenario involving fermionic dark matter (χ) and singlet scalar mediators that may account for the Galactic center GeV γ-ray excess while satisfying present direct detection constraints. CP violation in the scalar potential leads to a mixing between the Standard Model Higgs boson and the scalar singlet, resulting in three scalars, h_(1,2,3), of indefinite CP-transformation properties. This mixing enables s-wave χχ¯ annihilation into discalar states, followed by decays into four-fermion final states. The observed γ-ray spectrum can be fitted while respecting present direct detection bounds and Higgs boson properties for m_χ=60∼80 GeV, and m_(h_3)) ∼ m_χ. Searches for the Higgs exotic decay channel h_1 → h_3h_3 at the 14 TeV LHC should be able to further probe the parameter region favored by the γ-ray excess.https://resolver.caltech.edu/CaltechAUTHORS:20160601-141504526TeV lepton number violation: From neutrinoless double-β decay to the LHC
https://resolver.caltech.edu/CaltechAUTHORS:20160525-134733461
Year: 2016
DOI: 10.1103/PhysRevD.93.093002
We analyze the sensitivity of next-generation tonne-scale neutrinoless double-β decay (0νββ) experiments and searches for same-sign di-electrons plus jets at the Large Hadron Collider to TeV scale lepton number violating interactions. Taking into account previously unaccounted for physics and detector backgrounds at the LHC, renormalization group evolution, and long-range contributions to 0νββ nuclear matrix elements, we find that the reach of tonne-scale 0νββ generally exceeds that of the LHC for a class of simplified models. However, for a range of heavy particle masses near the TeV scale, the high luminosity LHC and tonne-scale 0νββ may provide complementary probes.https://resolver.caltech.edu/CaltechAUTHORS:20160525-134733461Singlet-catalyzed electroweak phase transitions in the 100 Te V frontier
https://resolver.caltech.edu/CaltechAUTHORS:20160824-080816851
Year: 2016
DOI: 10.1103/PhysRevD.94.035022
We study the prospects for probing a gauge singlet scalar-driven strong first-order electroweak phase transition with a future proton-proton collider in the 100 TeV range. Singlet-Higgs mixing enables resonantly enhanced di-Higgs production, potentially aiding discovery prospects. We perform Monte Carlo scans of the parameter space to identify regions associated with a strong first-order electroweak phase transition, analyze the corresponding di-Higgs signal, and select a set of benchmark points that span the range of di-Higgs signal strengths. For the bbγγ and 4τ final states, we investigate discovery prospects for each benchmark point for the high-luminosity phase of the Large Hadron Collider and for a future pp collider with √s = 50, 100, or 200 TeV. We find that any of these future collider scenarios could significantly extend the reach beyond that of the high-luminosity LHC, and that with √s = 100 TeV (200 TeV) and 30 ab^(−1), the full region of parameter space favorable to strong first-order electroweak phase transitions is almost fully (fully) discoverable.https://resolver.caltech.edu/CaltechAUTHORS:20160824-080816851Right-handed neutrinos and T-violating, P-conserving interactions
https://resolver.caltech.edu/CaltechAUTHORS:20170407-082350616
Year: 2017
DOI: 10.1016/j.physletb.2016.11.061
We show that experimental probes of the P-conserving, T-violating triple correlation in polarized neutron or nuclear β -decay provide a unique probe of possible T-violation at the TeV scale in the presence of right-handed neutrinos. In contrast to other possible sources of semileptonic T-violation involving only left-handed neutrinos, those involving right-handed neutrinos are relatively unconstrained by present limits on the permanent electric dipole moments of the electron, neutral atoms, and the neutron. On the other hand, LHC results for pp→e+ missing transverse energy imply that an order of magnitude of improvement in D-coefficient sensitivity would be needed for discovery. Finally, we discuss the interplay with the scale of neutrino mass and naturalness considerations.https://resolver.caltech.edu/CaltechAUTHORS:20170407-082350616Dark gauge bosons: LHC signatures of non-Abelian kinetic mixing
https://resolver.caltech.edu/CaltechAUTHORS:20170526-090230816
Year: 2017
DOI: 10.1016/j.physletb.2017.04.037
We consider non-abelian kinetic mixing between the Standard Model SU(2)_L and a dark sector U(1)′ gauge group associated with the presence of a scalar SU(2)_L triplet. The magnitude of the resulting dark photon coupling ϵ is determined by the ratio of the triplet vacuum expectation value, constrained to by ≲4 GeV by electroweak precision tests, to the scale Λ of the effective theory. The corresponding effective operator Wilson coefficient can be O(1) while accommodating null results for dark photon searches, allowing for a distinctive LHC dark photon phenomenology. After outlining the possible LHC signatures, we illustrate by recasting current ATLAS dark photon results into the non-abelian mixing context.https://resolver.caltech.edu/CaltechAUTHORS:20170526-090230816Resonant di-Higgs boson production in the b¯bWW channel: Probing the electroweak phase transition at the LHC
https://resolver.caltech.edu/CaltechAUTHORS:20170815-091700468
Year: 2017
DOI: 10.1103/PhysRevD.96.035007
We analyze the prospects for resonant di-Higgs production searches at the LHC in the b¯bW+W− (W+→ℓ+ν_ℓ, W−→ℓ−¯ν_ℓ) channel, as a probe of the nature of the electroweak phase transition in Higgs portal extensions of the Standard Model. In order to maximize the sensitivity in this final state, we develop a new algorithm for the reconstruction of the b¯bW+W− invariant mass in the presence of neutrinos from the W decays, building from a technique developed for the reconstruction of resonances decaying to τ+τ− pairs. We show that resonant di-Higgs production in the b¯bW+W−channel could be a competitive probe of the electroweak phase transition already with the data sets to be collected by the CMS and ATLAS experiments in run 2 of the LHC. The increase in sensitivity with larger amounts of data accumulated during the high-luminosity LHC phase can be sufficient to enable a potential discovery of the resonant di-Higgs production in this channel.https://resolver.caltech.edu/CaltechAUTHORS:20170815-091700468Parity-violating and time-reversal-violating pion-nucleon couplings: Higher order chiral matching relations
https://resolver.caltech.edu/CaltechAUTHORS:20170503-155039376
Year: 2017
DOI: 10.1103/PhysRevC.96.065204
Parity-violating and time-reversal-violating (PVTV) pion-nucleon couplings govern the magnitude of long-range contributions to nucleon and atomic electric-dipole moments. When these couplings arise from chiral-symmetry-breaking charge-parity-violating (CP-violating) operators, such as the QCD θ term or quark chromoelectric dipole moments, one may relate hadronic matrix elements entering the PVTV couplings to nucleon and pion mass shifts by exploiting the corresponding chiral transformation properties at leading order in the chiral expansion. We compute the higher order contributions to the lowest order relations arising from chiral loops and next-to-next-to leading order operators. We find that, for the QCD θ term, the higher order contributions are analytic in the quark masses, while for the quark chromoelectric dipole moments and chiral-symmetry-breaking four-quark operators, the matching relations also receive nonanalytic corrections. Numerical estimates suggest that, for the isoscalar PVTV pion-nucleon coupling, the higher order corrections may be as large as ∼20%, while for the isovector coupling, more substantial corrections are possible.https://resolver.caltech.edu/CaltechAUTHORS:20170503-155039376Lepton-flavored electroweak baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20180103-155520714
Year: 2017
DOI: 10.1103/PhysRevD.96.115034
We explore lepton-flavored electroweak baryogenesis, driven by CP-violation in leptonic Yukawa sector, using the τ−μ system in the two Higgs doublet model as an example. This setup generically yields, together with the flavor-changing decay h→τμ, a tree-level Jarlskog invariant that can drive dynamical generation of baryon asymmetry during a first-order electroweak phase transition and results in CP-violating effects in the decay h→ττ. We find that the observed baryon asymmetry can be generated in parameter space compatible with current experimental results for the decays h→τμ, h→ττ, and τ→μγ, as well as the present bound on the electric dipole moment of the electron. The baryon asymmetry generated is intrinsically correlated with the CP-violating decay h→ττ and the flavor-changing decay h→τμ, which thus may serve as "smoking guns" to test lepton-flavored electroweak baryogenesis.https://resolver.caltech.edu/CaltechAUTHORS:20180103-155520714CP-violation in the two Higgs doublet model: From the LHC to EDMs
https://resolver.caltech.edu/CaltechAUTHORS:20180201-112823006
Year: 2018
DOI: 10.1103/PhysRevD.97.015020
We study the prospective sensitivity to CP-violating two Higgs doublet models from the 14 TeV LHC and future electric dipole moment (EDM) experiments. We concentrate on the search for a resonant heavy Higgs that decays to a Z boson and a SM-like Higgs h, leading to the Z(ℓℓ)h(b¯b) final state. The prospective LHC reach is analyzed using the Boosted Decision Tree method. We illustrate the complementarity between the LHC and low energy EDM measurements and study the dependence of the physics reach on the degree of deviation from the alignment limit. In all cases, we find that there exists a large part of parameter space that is sensitive to both EDMs and LHC searches.https://resolver.caltech.edu/CaltechAUTHORS:20180201-112823006Standard model with a complex scalar singlet: Cosmological implications and theoretical considerations
https://resolver.caltech.edu/CaltechAUTHORS:20180108-124501468
Year: 2018
DOI: 10.1103/PhysRevD.97.015005
We analyze the theoretical and phenomenological considerations for the electroweak phase transition and dark matter in an extension of the standard model with a complex scalar singlet (cxSM). In contrast with earlier studies, we use a renormalization group improved scalar potential and treat its thermal history in a gauge-invariant manner. We find that the parameter space consistent with a strong first-order electroweak phase transition (SFOEWPT) and present dark matter phenomenological constraints is significantly restricted compared to results of a conventional, gauge-noninvariant analysis. In the simplest variant of the cxSM, recent LUX data and a SFOEWPT require a dark matter mass close to half the mass of the standard model-like Higgs boson. We also comment on various caveats regarding the perturbative treatment of the phase transition dynamics.https://resolver.caltech.edu/CaltechAUTHORS:20180108-124501468Top Down Electroweak Dipole Operators
https://resolver.caltech.edu/CaltechAUTHORS:20180413-103444632
Year: 2018
DOI: 10.1016/j.physletb.2018.04.022
We derive present constraints on, and prospective sensitivity to, the electric dipole moment (EDM) of the top quark (d_t) implied by searches for the EDMs of the electron and nucleons. Above the electroweak scale v, the d_t arises from two gauge invariant operators generated at a scale Λ≫v that also mix with the light fermion EDMs under renormalization group evolution at two-loop order. Bounds on the EDMs of first generation fermion systems thus imply bounds on |d_t|. Working in the leading log-squared approximation, we find that the present upper bound on |d_t| is 10^(−19) e cm for Λ=1 TeV, except in regions of finely tuned cancellations that allow for |d_t| to be up to fifty times larger. Future d_e and d_n probes may yield an order of magnitude increase in d_t sensitivity, while inclusion of a prospective proton EDM search may lead to an additional increase in reach.https://resolver.caltech.edu/CaltechAUTHORS:20180413-103444632Color breaking baryogenesis
https://resolver.caltech.edu/CaltechAUTHORS:20180608-145742067
Year: 2018
DOI: 10.1103/PhysRevD.97.123509
We propose a scenario that generates the observed baryon asymmetry of the Universe through a multistep phase transition in which SU(3) color symmetry is first broken and then restored. A spontaneous violation of B−L conservation leads to a contribution to the baryon asymmetry that becomes negligible in the final phase. The baryon asymmetry is therefore produced exclusively through the electroweak mechanism in the intermediate phase. We illustrate this scenario with a simple model that reproduces the observed baryon asymmetry. We discuss how future electric dipole moment and collider searches may probe this scenario, though future electric dipole moment searches would require an improved sensitivity of several orders of magnitude.https://resolver.caltech.edu/CaltechAUTHORS:20180608-145742067Coherent μ-e Conversion at Next-to-Leading Order
https://resolver.caltech.edu/CaltechAUTHORS:20171011-190335920
Year: 2018
DOI: 10.1103/PhysRevC.98.015208
We analyze next-to-leading-order (NLO) corrections and uncertainties for coherent μ−e conversion. The analysis is general, but numerical results focus on ^(27)Al, which will be used in the Muon-to-electron conversion (Mu2e) experiment. We obtain a simple expression for the branching ratio in terms of Wilson coefficients associated with possible physics beyond the standard model and a set of model-independent parameters determined solely by standard model dynamics. For scalar-mediated conversion, we find that NLO two-nucleon contributions can significantly decrease the branching ratio, potentially reducing the rate by as much as 50%. The pion-nucleon σ term and quark masses give the dominant sources of parametric uncertainty in this case. For vector-mediated conversion, the impact of NLO contributions is considerably less severe, while the present theoretical uncertainties are comparable to parametric uncertainties.https://resolver.caltech.edu/CaltechAUTHORS:20171011-190335920Doubly-charged scalars in the type II seesaw mechanism: Fundamental symmetry tests and high-energy searches
https://resolver.caltech.edu/CaltechAUTHORS:20180912-135435266
Year: 2018
DOI: 10.1103/physrevd.98.055013
We analyze the sensitivity of low-energy fundamental symmetry tests to interactions mediated by doubly-charged scalars that arise in type II seesaw models of neutrino mass and their left-right symmetric extensions. We focus on the next generation measurement of the parity-violating asymmetry in Møller scattering planned by the MOLLER collaboration at Jefferson Laboratory. We compare the MOLLER sensitivity to that of searches for charged lepton flavor violation (CLFV) and neutrinoless double beta-decay (0νββ-decay) as well as present and possible future high-energy collider probes. We show that for the simplest type-II seesaw scenario, CLFV searches have the greatest sensitivity. However, in a left-right symmetric extension where the scale of parity-breaking is decoupled from the SU(2)_R-breaking scale, the MOLLER experiment will provide a unique probe of scalar triplet interactions in the right-handed sector for a doubly-charged scalar mass up to ∼10 TeV and help elucidate the mechanism of 0νββ-decay.https://resolver.caltech.edu/CaltechAUTHORS:20180912-135435266Reduced Hadronic Uncertainty in the Determination of
V_(ud)
https://resolver.caltech.edu/CaltechAUTHORS:20181217-094749403
Year: 2018
DOI: 10.1103/PhysRevLett.121.241804
We analyze the universal radiative correction Δ^V_R to neutron and superallowed nuclear β decay by expressing the hadronic γW-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the γW interference structure function F^((0))_3. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of Δ^V_R = 0.02467(22), wherein the hadronic uncertainty is reduced. Assuming other standard model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of |V_(ud)| = 0.97370(14), raising tension with the first row Cabibbo-Kobayashi-Maskawa unitarity constraint. We comment on ways current and future experiments can provide input to our dispersive analysis.https://resolver.caltech.edu/CaltechAUTHORS:20181217-094749403Type-II seesaw scalar triplet model at a 100 TeV pp collider: discovery and higgs portal coupling determination
https://resolver.caltech.edu/CaltechAUTHORS:20190123-090848787
Year: 2019
DOI: 10.1007/jhep01(2019)101
We investigate the collider phenomenology of the scalar triplet particles in the Type-II seesaw model at a 100 TeV pp collider. Depending on triplet vacuum expectation value vΔ, the dominant discovery channels could be H++H−− and H±±H∓. We find the H±±H∓ → W±W±hW∓/ℓ±ℓ±hW∓ channels are promising for both model discovery at relatively large vΔ and determination of the Higgs portal couplings λ_4 and λ_5. We also find that these two channels are complementary to indirect determination of _λ4 from future precise measurements on h → γ γdecay rate. Together with pair production of the doubly-charged Higgs subsequently decaying into same-sign di-leptons, the H±±H∓ channels have the potential to cover a significant portion of the parameter space of the Type-II seesaw complex scalar triplet model.https://resolver.caltech.edu/CaltechAUTHORS:20190123-090848787Electric dipole moments from CP-violating scalar leptoquark interactions
https://resolver.caltech.edu/CaltechAUTHORS:20181126-082045545
Year: 2019
DOI: 10.1016/j.physletb.2018.11.016
We analyze the implications of CP-violating scalar leptoquark (LQ) interactions for experimental probes of parity- and time-reversal violating properties of polar molecules. These systems are predominantly sensitive to the electric dipole moment (EDM) of the electron and nuclear-spin-independent (NSID) electron–nucleon interaction. The LQ model can generate both a tree-level NSID interaction as well as the electron EDM at one-loop order. Including both interactions, we find that the NSID interaction can dominate the molecular response. For moderate values of couplings, the current experimental results give roughly two orders of magnitude stronger limits on the electron EDM than one would otherwise infer from a sole-source analysis.https://resolver.caltech.edu/CaltechAUTHORS:20181126-082045545Probing neutrino Dirac mass in left-right symmetric models at the LHC and next generation colliders
https://resolver.caltech.edu/CaltechAUTHORS:20190327-103330446
Year: 2019
DOI: 10.1103/PhysRevD.99.055042
We assess the sensitivity of the LHC, its high energy upgrade, and a prospective 100 TeV hadronic collider to the Dirac Yukawa coupling of the heavy neutrinos in left-right symmetric models (LRSMs). We focus specifically on the trilepton final state in regions of parameter space yielding prompt decays of the right-handed gauge bosons (W_R) and neutrinos (N_R). In the minimal LRSM, the Dirac Yukawa couplings are completely fixed in terms of the mass matrices for the heavy and light neutrinos. In this case, the trilepton signal provides a direct probe of the Dirac mass term for a fixed W_R and N_R mass. We find that while it is possible to discover the W_R at the LHC, probing the Dirac Yukawa couplings will require a 100 TeV pp collider. We also show that the observation of the trilepton signal at the LHC would indicate the presence of a nonminimal LRSM scenario.https://resolver.caltech.edu/CaltechAUTHORS:20190327-103330446Dispersive evaluation of the inner radiative correction in neutron and nuclear β decay
https://resolver.caltech.edu/CaltechAUTHORS:20190716-104707744
Year: 2019
DOI: 10.1103/physrevd.100.013001
We propose a novel dispersive treatment of the so-called inner radiative correction to the neutron and nuclear β decay. We show that it requires knowledge of the parity-violating structure function F^((0))_3 that arises from the interference of the axial vector charged current and the isoscalar part of the electromagnetic current. By isospin symmetry, we relate this structure function to the charged current inelastic scattering of neutrinos and antineutrinos. Applying this new data-driven analysis we obtain a new, more precise evaluation for the universal radiative correction Δ^(V,new)_R=0.02467(22) that supersedes the previous estimate by Marciano and Sirlin, Δ^V_R=0.02361(38). The substantial shift in the central value of Δ^V_R reflects in a respective shift of V_(ud) and a considerable tension in the unitarity constraint on the first row of the Cabibbo-Kobayashi-Maskawa matrix which is used as one of the most stringent constraints on new physics contributions in the charged current sector. We also point out that dispersion relations offer a unifying tool for treating hadronic and nuclear corrections within the same framework. We explore the potential of the dispersion relations for addressing the nuclear structure corrections absorbed in the Ft values, a crucial ingredient alongside Δ^V_R in extracting V_(ud) from superallowed nuclear decays. In particular, we estimate the quenching of the free neutron Born contribution in the nuclear environment, corresponding to a quasielastic single-nucleon knockout, and find a significantly stronger quenching effect as compared to currently used estimates based on the quenching of spin operators in nuclear transitions. This observation suggests that the currently used theoretical uncertainties of Ft values might be underestimated and require a renewed scrutiny, while emphasizing the importance of new, more precise measurements of the free neutron decay where nuclear corrections are absent.https://resolver.caltech.edu/CaltechAUTHORS:20190716-104707744Scalar electroweak multiplet dark matter
https://resolver.caltech.edu/CaltechAUTHORS:20190812-110605376
Year: 2019
DOI: 10.1007/jhep08(2019)058
We revisit the theory and phenomenology of scalar electroweak multiplet thermal dark matter. We derive the most general, renormalizable scalar potential, assuming the presence of the Standard Model Higgs doublet, H, and an electroweak multiplet Φ of arbitrary SU(2)_L rank and hypercharge, Y. We show that, in general, the Φ-H Higgs portal interactions depend on three, rather than two independent couplings as has been previously considered in the literature. For the phenomenologically viable case of Y = 0 multiplets, we focus on the septuplet and quintuplet cases, and consider the interplay of relic density and spin-independent direct detection cross section. We show that both the relic density and direct detection cross sections depend on a single linear combination of Higgs portal couplings, λ_(eff). For λ_(eff) ∼ O(1), present direct detection exclusion limits imply that the neutral component of a scalar electroweak multiplet would comprise a subdominant fraction of the observed DM relic density.https://resolver.caltech.edu/CaltechAUTHORS:20190812-110605376Electroweak baryogenesis with vector-like leptons and scalar singlets
https://resolver.caltech.edu/CaltechAUTHORS:20190909-093503441
Year: 2019
DOI: 10.1007/jhep09(2019)012
We investigate the viability of electroweak baryogenesis in a model with a first order electroweak phase transition induced by the addition of two gauge singlet scalars. A vector-like lepton doublet is introduced in order to provide CP violating interactions with the singlets and Standard Model leptons, and the asymmetry generation dynamics are examined using the vacuum expectation value insertion approximation. We find that such a model is readily capable of generating sufficient baryon asymmetry while satisfying electron electric dipole moment and collider phenomenology constraints.https://resolver.caltech.edu/CaltechAUTHORS:20190909-093503441Probing a scalar singlet-catalyzed electroweak phase transition with resonant di-Higgs boson production in the 4b channel
https://resolver.caltech.edu/CaltechAUTHORS:20191028-104319476
Year: 2019
DOI: 10.1103/physrevd.100.075035
We investigate the prospective reach of the 14 TeV HL-LHC for resonant production of a heavy Higgs boson that decays to two SM-like Higgs bosons in the 4b final state in the scalar singlet extended Standard Model. We focus on the reach for choices of parameters yielding a strong first order electroweak phase transition. The event selection follows the 4b analysis by the ATLAS Collaboration, enhanced with the use of a boosted decision tree method to optimize the discrimination between signal and background events. The output of the multivariate discriminant is used directly in the statistical analysis. The prospective reach of the 4b channel is compatible with previous projections for the bbγγ and 4τ channels for heavy Higgs boson mass m₂ below 500 GeV and superior to these channels for m₂>500 GeV. With 3 ab⁻¹ of integrated luminosity, it is possible to discover the heavy Higgs boson in the 4b channel for m₂<500 GeV in regions of parameter space yielding a strong first order electroweak phase transition and satisfying all other phenomenological constraintshttps://resolver.caltech.edu/CaltechAUTHORS:20191028-104319476Nonperturbative analysis of the gravitational waves from a first-order electroweak phase transition
https://resolver.caltech.edu/CaltechAUTHORS:20190910-125538082
Year: 2019
DOI: 10.1103/PhysRevD.100.115024
We present the first end-to-end nonperturbative analysis of the gravitational wave power spectrum from a thermal first-order electroweak phase transition (EWPT), using the framework of dimensionally reduced effective field theory and preexisting nonperturbative simulation results. We are able to show that a first-order EWPT in any beyond the Standard Model (BSM) scenario that can be described by a Standard Model-like effective theory at long distances will produce gravitational wave signatures too weak to be observed at existing and planned detectors. This implies that colliders are likely to provide the best chance of exploring the phase structure of such theories, while transitions strong enough to be detected at gravitational wave experiments require either previously neglected higher-dimension operators or light BSM fields to be included in the dimensionally reduced effective theory and therefore necessitate dedicated nonperturbative studies. As a concrete application, we analyze the real singlet-extended Standard Model and identify regions of parameter space with single-step first-order transitions, comparing our findings to those obtained using a fully perturbative method. We discuss the prospects for exploring the electroweak phase diagram in this model at collider and gravitational wave experiments in light of our nonperturbative results.https://resolver.caltech.edu/CaltechAUTHORS:20190910-125538082CP-violating dark photon interaction
https://resolver.caltech.edu/CaltechAUTHORS:20200409-115739992
Year: 2020
DOI: 10.1103/physrevd.101.075016
We introduce a scenario for CP-violating (CPV) dark photon interactions in the context of non-abelian kinetic mixing. Assuming an effective field theory that extends the Standard Model (SM) field content with an additional U(1) gauge boson (X) and a SU(2_)L triplet scalar, we show that there exist both CP-conserving and CPV dimension five operators involving these new degrees of freedom and the SM SU(2)_L gauge bosons. The former yields kinetic mixing between the X and the neutral SU(2)_L gauge boson (yielding the dark photon), while the latter induces CPV interactions of the dark photon with the SM particles. We discuss experimental probes of these interactions using searches for permanent electric dipole moments (EDMs) and di-jet correlations in high-energy pp collisions. It is found that the experimental limit on the electron EDM currently gives the strongest restriction on the CPV interaction. In principle, high energy pp collisions provide a complementary probe through azimuthal angular correlations of the two forward tagging jets in vector boson fusion. In practice, observation of the associated CPV asymmetry is likely to be challenging.https://resolver.caltech.edu/CaltechAUTHORS:20200409-115739992Two-step electroweak symmetry-breaking: theory meets experiment
https://resolver.caltech.edu/CaltechAUTHORS:20200512-122035425
Year: 2020
DOI: 10.1007/jhep05(2020)050
We study the phenomenology of a hypercharge-zero SU (2) triplet scalar whose existence is motivated by two-step electroweak symmetry-breaking. We consider both the possibility that the triplets are stable and contribute to the dark matter density, or that they decay via mixing with the standard model Higgs boson. The former is constrained by disappearing charged track searches at the LHC and by dark matter direct detection experiments, while the latter is constrained by existing multilepton collider searches. We find that a two-step electroweak phase transition involving a stable triplet with a negative quadratic term is ruled out by direct detection searches, while an unstable triplet with a mass less than 230 GeV is excluded at 95% confidence level.https://resolver.caltech.edu/CaltechAUTHORS:20200512-122035425Exotic Higgs boson decays and the electroweak phase transition
https://resolver.caltech.edu/CaltechAUTHORS:20200625-094628686
Year: 2020
DOI: 10.1103/PhysRevD.101.115035
Light new physics weakly coupled to the Higgs can induce a strong first-order electroweak phase transition (EWPT). Here, we argue that scenarios in which the EWPT is driven first-order by a light scalar with mass between ∼10 GeV − m_h/2 and small mixing with the Higgs will be conclusively probed by the high-luminosity LHC and future Higgs factories. Our arguments are based on analytic and numerical studies of the finite-temperature effective potential and provide a well-motivated target for exotic Higgs decay searches at the LHC and future lepton colliders.https://resolver.caltech.edu/CaltechAUTHORS:20200625-094628686The electroweak phase transition: a collider target
https://resolver.caltech.edu/CaltechAUTHORS:20200930-145049373
Year: 2020
DOI: 10.1007/jhep09(2020)179
Determining the thermal history of electroweak symmetry breaking (EWSB) is an important challenge for particle physics and cosmology. Lattice simulations indicate that EWSB in the Standard Model (SM) occurs through a crossover transition, while the presence of new physics beyond the SM could alter this thermal history. The occurrence of a first order EWSB transition would be particularly interesting, providing the needed pre-conditions for generation of the cosmic matter-antimatter asymmetry and sources for potentially observable gravitational radiation. I provide simple, generic arguments that if such an alternate thermal history exists, the new particles involved cannot be too heavy with respect to the SM electroweak temperature, nor can they interact too feebly with the SM Higgs boson. These arguments do not rely on the decoupling limit. I derive corresponding quantitative expectations for masses and interaction strengths which imply that their effects could in principle be observed (or ruled out) by prospective next generation high energy colliders. The simple, generic arguments provide a quantitative, parametric understanding of results obtained in a wide range of explicit model studies; relate them explicitly to the electroweak temperature; and delineate broad contours of collider phenomenology pertaining to a non-standard history of EWSB.https://resolver.caltech.edu/CaltechAUTHORS:20200930-145049373Collider probes of real triplet scalar dark matter
https://resolver.caltech.edu/CaltechAUTHORS:20210129-071422414
Year: 2021
DOI: 10.1007/jhep01(2021)198
We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100 TeV pp collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in pp collisions, the charged triplet scalar decays to the neutral component plus a soft pion or soft lepton pair, yielding a disappearing charged track in the detector. We recast current 13 TeV LHC searches for disappearing tracks, and find that the LHC presently excludes a real triplet scalar lighter than 248 (275) GeV, for a mass splitting of 172 (160) MeV with ℒ = 36 fb⁻¹. The reach can extend to 497 (520) GeV with the collection of 3000 fb⁻¹. We extrapolate the 13 TeV analysis to a prospective 100 TeV pp collider, and find that a ∼ 3 TeV triplet scalar could be discoverable with ℒ = 30 ab⁻¹, depending on the degree to which pile up effects are under control. We also investigate the dark matter candidate in our model and corresponding present and prospective constraints from dark matter direct detection. We find that currently XENON1T can exclude a real triplet dark matter lighter than ∼ 3 TeV for a Higgs portal coupling of order one or larger, and the future XENON20T will cover almost the entire dark matter viable parameter space except for vanishingly small portal coupling.https://resolver.caltech.edu/CaltechAUTHORS:20210129-071422414Left-Right Symmetry and Leading Contributions to Neutrinoless Double Beta Decay
https://resolver.caltech.edu/CaltechAUTHORS:20210421-083929757
Year: 2021
DOI: 10.1103/physrevlett.126.151801
We study the impact of the mixing (LR mixing) between the standard model W boson and its hypothetical, heavier right-handed parter W_R on the neutrinoless double beta decay (0νββ decay) rate. Our study is done in the minimal left-right symmetric model assuming a type-II dominance scenario with charge conjugation as the left-right symmetry. We then show that the 0νββ decay rate may be dominated by the contribution proportional to this LR mixing, which at the hadronic level induces the leading-order contribution to the interaction between two pions and two charged leptons. The resulting long-range pion exchange contribution can significantly enhance the decay rate compared to previously considered short-range contributions. Finally, we find that even if future cosmological experiments rule out the inverted hierarchy for neutrino masses, there are still good prospects for a positive signal in the next generation of 0νββ decay experiments.https://resolver.caltech.edu/CaltechAUTHORS:20210421-083929757