Cosmic birefringence (CB)—a rotation of photon-polarization plane in vacuum—is a generic signature of new scalar fields that could provide dark energy. Previously, WMAP observations excluded a uniform CB-rotation angle larger than a degree.
In this thesis, we develop a minimum-variance–estimator formalism for reconstructing direction-dependent rotation from full-sky CMB maps, and forecast more than an order-of-magnitude improvement in sensitivity with incoming Planck data and future satellite missions. Next, we perform the first analysis of WMAP-7 data to look for rotation-angle anisotropies and report null detection of the rotation-angle power-spectrum multipoles below L=512, constraining quadrupole amplitude of a scale-invariant power to less than one degree. We further explore the use of a cross-correlation between CMB temperature and the rotation for detecting the CB signal, for different quintessence models. We find that it may improve sensitivity in case of marginal detection, and provide an empirical handle for distinguishing details of new physics indicated by CB.
We then consider other parity-violating physics beyond standard models—in particular, a chiral inflationary-gravitational-wave background. We show that WMAP has no constraining power, while a cosmic-variance–limited experiment would be capable of detecting only a large parity violation. In case of a strong detection of EB/TB correlations, CB can be readily distinguished from chiral gravity waves.
We next adopt our CB analysis to investigate patchy screening of the CMB, driven by inhomogeneities during the Epoch of Reionization (EoR). We constrain a toy model of reionization with WMAP-7 data, and show that data from Planck should start approaching interesting portions of the EoR parameter space and can be used to exclude reionization tomographies with large ionized bubbles.
In light of the upcoming data from low-frequency radio observations of the redshifted 21-cm line from the EoR, we examine probability-distribution functions (PDFs) and difference PDFs of the simulated 21-cm brightness temperature, and discuss the information that can be recovered using these statistics. We find that PDFs are insensitive to details of small-scale physics, but highly sensitive to the properties of the ionizing sources and the size of ionized bubbles.
Finally, we discuss prospects for related future investigations.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/Q603-SH04, author = {Lee, Samuel Kuhnman}, title = {Three Paths to Particle Dark Matter}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/Q603-SH04}, url = {https://resolver.caltech.edu/CaltechTHESIS:05152012-125430182}, abstract = {
In this thesis, we explore examples of each of the three primary strategies for the detection of particle dark matter: indirect detection, direct detection, and collider production.
We first examine the indirect detection of weakly interacting massive particle (WIMP) dark matter via the gamma-ray photons produced by astrophysical WIMP annihilation. Such photons may be observed by the Fermi Gamma-ray Space Telescope. We propose the gamma-ray-flux probability distribution function (PDF) as a probe of the Galactic halo substructure predicted to exist by N-body simulations. The PDF is calculated for a phenomenological model of halo substructure; it is shown that the PDF may allow a statistical detection of substructure.
Next, we consider the direct detection of WIMPs. We explore the ability of directional nuclear-recoil detectors to constrain the local velocity distribution of WIMP dark matter by performing Bayesian parameter estimation on simulated recoil-event data sets. We discuss in detail how directional information, when combined with measurements of the recoil-energy spectrum, helps break degeneracies in the velocity-distribution parameters. Considering the possibility that velocity structures such as cold tidal streams or a dark disk may also be present in addition to the Galactic halo, we discuss the potential of upcoming experiments to probe such structures.
We then study the collider production of light gravitino dark matter. Light gravitino production results in spectacular signals, including di-photons, delayed photons, kinked charged tracks, and heavy metastable charged particles. We find that observable numbers of light-gravitino events may be found in future collider data sets. Remarkably, this data is also well suited to distinguish between scenarios with light gravitino dark matter, with striking implications for early-Universe cosmology.
Finally, we investigate the related matter of radiative corrections to the decay rate of charged fermions caused by the presence of a thermal bath of photons. The cancellation of finite-temperature infrared divergences in the decay rate is described in detail. Temperature-dependent radiative corrections to the two-body decay of a hypothetical charged fermion and to electroweak decays of a muon are given. We touch upon possible implications of these results for charged particles in the early Universe.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/VJ9N-0J70, author = {Pullen, Anthony Robert}, title = {A Survey of Results in Modern Precision Cosmology}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/VJ9N-0J70}, url = {https://resolver.caltech.edu/CaltechTHESIS:05042011-123721947}, abstract = {In this work, we evaluate the evidence for some of the more exotic ideas in cosmology for which scientists are searching today, these anomalies being dark matter, statistical anisotropy, and non-Gaussianity. Dark matter, which is estimated to comprise 83% of the matter in our universe, still remains undiscovered. We search data from the Energetic Gamma Ray Experiment Telescope for a gamma-ray line in the energy range 0.1-10 GeV from the 10X10 degree region around the Galactic center. Our null results lead to upper limits to the line flux from the Galactic center. We use these limits to place constraints on the particle’s two-photon annihilation cross section as a function of its mass, which we show to produce stronger limits than those derived from measurements of the 511-keV line.
Next, we investigate the possibility that cosmic inflation deviates from statistical isotropy. Statistical isotropy is a common assumption that should be tested. We develop cosmic-microwave-background statistics for a direction-dependent primordial power spectrum. We then construct minimum-variance estimators for the coefficients of a spherical-harmonic expansion of the direction-dependence of the primordial power spectrum. We find that a power quadrupole as small as 2.0% can be detected by the Planck satellite. We also constrain statistical anisotropy of the quadrupolar form using a sample of photometric luminous red galaxies measured by the Sloan Digital Sky Survey. Not detecting evidence, we place limits on an axisymmetric quadrupole model. We find discrepancies between our results and a cosmic microwave background analysis that claimed a positive detection. We also find the quadrupolar asymmetry limits to be between -0.41 and 0.38 with 95% probability.
Finally, we prepare a search for evidence of non-Gaussianity in the the early universe. Scale-dependent bias has been shown to be a competitive probe of non-Gaussianity in large-scale structure, and constraints have been calculated using various tracers of the matter distribution. We seek to extend this analysis to the latest sample of photometric quasars measured by the Sloan Digital Sky Survey to search for evidence of scale-dependent bias in large-scale structure. Specifically we construct three data samples at various redshifts, removing various systematic effects. We calculate the cross-correlation angular power spectra between two of the data samples to search for any remaining systematics. We find a positive detection on large scales, which leads us to the conclusion that more systematics testing is needed to render this QSO catalog useful to constrain non-Gaussianity.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/EN34-1095, author = {Grin, Daniel}, title = {The Lukewarm Frontier: Some Cosmological Consequences of ‘Low Energy’ Physics}, school = {California Institute of Technology}, year = {2010}, doi = {10.7907/EN34-1095}, url = {https://resolver.caltech.edu/CaltechTHESIS:05312010-162432249}, abstract = {In this thesis, we present four projects featuring low characteristic energy scales relative to the scales relevant for supersymmetric dark matter production or inflation. We present a telescope search for decaying relic axions in the 3 − 8 eV mass range. We utilize larger telescope exposure and superior cluster mass modeling to improve sensitivity. Our results impose new stringent limits to the two-photon coupling or relic density of axions. We extend these results to non-standard sterile neutrinos.
We then reconsider cosmological constraints to axions. Our understanding of physics before big-bang nucleosynthesis is tenuous, and after arguing that a non-standard thermal history before nucleosynthesis is plausible and perhaps even natural, we calculate the abundance and typical momenta of thermal axions in such scenarios. We generalize existing cosmological constraints to axions, showing that the allowed axion mass range expands significantly in non-standard thermal histories. We then estimate the sensitivity of future experiments to axion masses and reheating temperatures.
We then study the ~ eV-scale physics of cosmological hydrogen ~ 10^4 states of hydrogen up to a maximum n ~ 250, and studying the associated convergence problem. We show that the recombination history is sufficiently converged for analysis of microwave anisotropy data from the Planck satellite if the maximum n ~ 128, and that previously ignored electric quadrupole transitions are indeed negligible to the precision necessary for Planck.
We conclude by presenting a new astrophysical limit to effective field theories of gravity in which the graviton propagator is damped at energies greater than a milli-eV.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/ST6B-1S91, author = {Erickcek, Adrienne Lynn}, title = {The Consequences of Modifying Fundamental Cosmological Theories}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/ST6B-1S91}, url = {https://resolver.caltech.edu/CaltechETD:etd-05292009-132414}, abstract = {
In this work, we examine alternatives to three fundamental cosmological theories: extended Press-Schechter merger theory, general relativity, and single-field inflation, and derive their observational consequences. The extended Press-Schechter merger rate for dark matter haloes is mathematically inconsistent and double-valued, and yet it has been widely applied in cosmology. One such application is the merger rate of supermassive black holes, and we show that the two predictions for this rate from extended Press-Schechter merger theory are nearly equal. We then compare the supermassive-black-hole merger rate derived from the extended Press-Schechter merger formalism to the rate derived from an alternate theory, in which halo merger rates are obtained by inverting the coagulation equation.
Next, we show how two modifications to general relativity may be tested inside the Solar System. First we consider f(R) gravity, which was proposed to explain late-time cosmic acceleration. We find that several forms of f(R) gravity are inconsistent with observations, and we establish a set of criteria that determines whether or not a given form of f(R) gravity is ruled out by Solar System gravitational tests. Second, we study Chern-Simons gravity: a parity-violating theory inspired by string theory. We find that Chern-Simons gravity predicts orbital precessions that are different from those predicted by general relativity, and we use the motion of satellites to constrain the Chern-Simons coupling parameter.
Finally, we consider an alternative to single-field inflation; in the curvaton scenario, the inflaton does not generate all of the primordial perturbations. Using this theory, we propose an origin for the hemispherical power asymmetry that has been observed in the cosmic microwave background on large angular scales. While this asymmetry cannot be produced by a superhorizon fluctuation in the inflaton field, it may be generated by a superhorizon fluctuation in the curvaton field. A superhorizon fluctuation would also induce large-scale anisotropies in the cosmic microwave background; we analyze this effect and prove that our model is consistent with observations. We also show how the power asymmetry may be suppressed on smaller scales if the curvaton creates isocurvature perturbations when it decays.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/SY21-6Z52, author = {Smith, Tristan Laine}, title = {The Gravity of the Situation}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/SY21-6Z52}, url = {https://resolver.caltech.edu/CaltechETD:etd-05282008-153540}, abstract = {In this thesis we examine several ways in which we can explore the early universe through gravitational-waves and the fundamental nature of gravity through cosmology and observations of dynamics within the solar system. Both of these topics have taken center stage, as we are living at a unique time which promises to bring fundamental insights into the nature of gravity with the discovery of new binary pulsar systems, the building of increasingly precise solar system and tabletop experiments and the birth of gravitational-wave observatories– to name a few recent and upcoming advances.
We first discuss whether we may be able to directly detect gravitational waves from inflation using future space-based interferometers. We then describe how the direct detection of inflationary gravitational waves will allow us to probe the fundamental physics that operated at the earliest moments of the universe. Next, a new constraint to a general cosmological gravitational wave background is presented using the observations of the cosmic microwave background. Moving away from general relativity, we consider alternative theories of gravity. One reason to consider alternative theories of gravity is the observation that the expansion of the universe is currently accelerating. It is possible that this accelerated expansion is due to a modification of gravity. However, any theory that modifies gravity in order to produce accelerated expansion must also conform to the dynamics that we observe within the Solar System. We discuss how the observation of the deflection of light around the Sun places severe limitations on a particular modified gravity theory, known as f(R) gravity. Our discussion of f(R) gravity leads us to ask whether the parameterized post Newtonian parameter, γPPN, takes on a universal value. We identify measurements made of strong lensing around early type galaxies in the Sloan Lens ACS (SLACS) survey as a first step in performing this new test of gravity. Finally, we explore some consequences of Chern-Simons gravity. One of the unique aspects of Chern-Simons gravity is that it introduces parity violation into the gravitational sector. As a consequence, it predicts a different gravitomagnetic field around the rotating Earth than is predicted in general relativity. We show how recent measurements of this gravitomagnetic field made by observing the two LAser GEOdynamics Satellites (LAGEOS) and Gravity Probe B satellites constrain Chern-Simons gravity. Finally, we discuss how future observations of binary pulsar systems may allow for a more general exploration of the gravitomagnetic structure around rotating objects.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/W3BF-8Q61, author = {Pritchard, Jonathan Robin}, title = {Extracting the Cosmic History from Diffuse Backgrounds}, school = {California Institute of Technology}, year = {2007}, doi = {10.7907/W3BF-8Q61}, url = {https://resolver.caltech.edu/CaltechETD:etd-05292007-112654}, abstract = {
The modern picture of the Universe resembles a detective novel with the first page and the middle chapters removed and the ending unwritten. Observations of the cosmic microwave background (CMB) have given cosmologists a snapshot of the Universe when it was only a few hundred thousand years old. At the same time, large galaxy surveys, such as SDSS and 2dF, have shed light on the distribution of matter in the local Universe. From the combination of these two data sets, cosmological parameters can be measured to percent accuracy. Two main frontiers remain: inflation, the domain of high-energy physics, and the epoch of reionization, the period connecting the linear age of the CMB with that of the present day. Added to this are the indications from supernovae of an acceleration in the expansion rate suggesting modifications to gravity or the presence of an esoteric new form of energy.
In this work, we investigate uses of various radiation backgrounds for probing the different epochs of this cosmic history. We examine (i) the use of B-mode polarization of the CMB induced by an inflationary gravitational wave background to probe inflation, (ii) the importance of higher Lyman series photons in pumping of the 21 cm line and the consequences for the 21 cm signal from the first stars, (iii) the atomic physics of Lyman series photon scattering in the intergalactic medium and the consequences for heating and coupling of the 21 cm line, (iv) the possibility of using the 21 cm line to probe inhomogeneous X-ray heating of the IGM by a population of early X-ray sources, and (v) the impact of inhomogeneous reionization on galaxy formation and the consequences for our ability to use large galaxy surveys to constrain dark energy. Together, these chapters significantly extend our understanding of important windows into the early Universe.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/V8PX-AE66, author = {Weinberg, Nevin Nachum}, title = {I. Ash Injection and Exposure During Radius Expansion Type I X-Ray Bursts. II. Stellar Dynamics at the Galactic Center. III. Weak Gravitational Lensing by Dark Matter Concentrations}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/V8PX-AE66}, url = {https://resolver.caltech.edu/CaltechETD:etd-06022005-151603}, abstract = {The studies presented herein are on three distinct topics in astrophysics:
I. We solve for the evolution of the vertical extent of the convective region of a neutron star atmosphere during a type I X-ray burst. The convective region is well-mixed with ashes of nuclear burning, and its extent determines the burst rise time. We show that the maximum extent of the convective region during photospheric radius expansion (PRE) bursts can be sufficiently great that some ashes of burning are: (1) ejected by the radiation-driven wind during the PRE phase and, (2) exposed at the neutron star surface following the PRE phase. We calculate the expected column density of ashes in hydrogen-like states and find that the resulting photoionization edges should be detectable with current high spectral resolution X-ray telescopes. A detection would probe the burst nuclear burning processes and might enable a measurement of the neutron star gravitational redshift.
This thesis examines two predictions of general relativity: weak lensing and gravitational waves. The cosmic microwave background (CMB) is gravitationally lensed by the large-scale structure between the observer and the last-scattering surface. This weak lensing induces non-Gaussian correlations that can be used to construct estimators for the deflection field. The error and bias of these estimators are derived and used to analyze the viability of lensing reconstruction for future CMB experiments.
Weak lensing also affects the one-point probability distribution function of the CMB. The skewness and kurtosis induced by lensing and the Sunayev-Zel’dovich (SZ) effect are calculated as functions of the angular smoothing scale of the map. While these functions offer the advantage of easy computability, only the skewness from lensing-SZ correlations can potentially be detected, even in the limit of the largest amplitude fluctuations allowed by observation.
Lensing estimators are also essential to constrain inflation, the favored explanation for large-scale isotropy and the origin of primordial perturbations. B-mode polarization is considered to be a “smoking-gun” signature of inflation, and lensing estimators can be used to recover primordial B-modes from lensing-induced contamination. The ability of future CMB experiments to constrain inflation is assessed as functions of survey size and instrumental sensitivity.
A final application of lensing estimators is to constrain a possible cutoff in primordial density perturbations on near-horizon scales. The paucity of independent modes on such scales limits the statistical certainty of such a constraint. Measurements of the deflection field can be used to constrain at the 3-sigma level the existence of a cutoff large enough to account for current CMB observations.
A final chapter of this thesis considers an independent topic: the gravitational-wave (GW) signature of a binary inspiral into a horizonless object. If the supermassive objects at galactic centers lack the horizons of traditional black holes, inspiraling objects could emit GWs after passing within their surfaces. The GWs produced by such an inspiral are calculated, revealing distinctive features potentially observable by future GW observatories.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/52QC-H668, author = {Sigurdson, Kris Raymond}, title = {Variations on the Standard Model of the Universe}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/52QC-H668}, url = {https://resolver.caltech.edu/CaltechETD:etd-05272005-141451}, abstract = {In the past decade, due to compelling measurements of the angular power spectrum of the cosmic microwave background (CMB) radiation, the large-scale matter distribution, the recent acceleration of the expansion rate of the Universe over cosmic time, and the current expansion rate (the Hubble constant), cosmology has culminated in a standard model of the Universe. By connecting this standard cosmological model with predictive theories of physics we can hope to look for signatures of these theories in the data. Along this line of inquiry we consider in this thesis: (i) the effects on CMB temperature and polarization anisotropies of spatial fluctuations of the fine-structure parameter alpha between causally disconnected regions of the Universe at the time of recombination, (ii) the suppression of the small-scale matter power spectrum due to the decay of charged matter to dark matter prior to recombination, (iii) the consequences of a neutral dark-matter particle with a nonzero electric and/or magnetic dipole moment, (iv) how charged-particles decaying in the early Universe can induce a scale-dependent or ‘running’ spectral index in the small-scale matter power spectrum and examples of this effect in minimal supersymmetric models in which the lightest neutralino is a viable cold-dark-matter candidate. With improved tests and cross-checks of standard-cosmological-model predictions we can search for anomalies that may reveal the character of the underlying physics. In this direction we propose in this thesis: (v) a new method for removing the effect of gravitational lensing from maps of CMB polarization anisotropies using observations of anisotropies or structures in the cosmic 21-cm radiation, (vi) that measurements of fluctuations in the absorption of CMB photons by hydrogen in the 21-cm line and deuterium in the 92-cm line during the cosmic dark ages could be used to determine the primordial deuterium abundance.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, } @phdthesis{10.7907/X9XT-YT35, author = {Santos, Michael Robert}, title = {Galaxy Formation Near the Epoch of Reionization}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/X9XT-YT35}, url = {https://resolver.caltech.edu/CaltechETD:etd-05182004-154315}, abstract = {I present five explorations of the formation of early galaxies near the epoch of reionization: observable phenomena that demonstrate the interaction between galaxy formation and the intergalactic medium.
I calculated the contribution of the first stars (Pop III) to the cosmic infrared background (CIRB). Pop III stars produced the observed unexplained component of the NIR CIRB if they were very massive and formed efficiently over a redshift range 25 ≳ z ≳ 7. A small escape fraction of ionizing photons from the nebular gas immediately surrounding the Pop III stars enhances the Pop III CIRB signal.
I calculated the effect of radiative transfer through the intergalactic medium (IGM) on the observed properties of Lyman alpha emission lines from z ≳ 6 galaxies. The detection of a Lyman alpha emitting galaxy at z = 6.5 resulted in claims that the universe was mostly ionized there. With existing information about the source galaxy it is almost impossible to deduce the ionization state of the z = 6.5 IGM, especially if there were galactic-scale super-winds.
I present a method to infer the stellar population responsible for completing reionization. We simulated helium and hydrogen absorption along lines-of-sight toward high-redshift QSOs assuming either Pop II or Pop III stars dominated the UV background at z=5. The final SDSS quasar sample may contain a quasar/line-of-sight combination that constrains the nature of the dominant ionizing sources only 300 Myr after the end of reionization.
I present an observational survey of low-luminosity Lyman alpha emitting galaxies at 4.5 < z < 6.7. This unprecedented survey utilized strong lensing by rich clusters of galaxies at intermediate redshifts to discover six likely Lyman alpha emitting galaxies. The z ~ 5 Lyman alpha luminosity function may be flatter than the mass function of dark matter halos, a sign of suppression of the star-formation efficiency in low-mass halos. However, our data by themselves are consistent with the slope of the halo mass function.
I modeled the formation of metal-poor globular cluster systems (GCSs), invoking reionization to explain the bimodality observed in GCS metallicity distributions. The model reproduces the mass and spatial extent of the Milky Way metal-poor GCS, and also the increasing number of metal-poor globular clusters per unit galaxy mass for galaxies in richer environments, as observed.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Kamionkowski, Marc P.}, }