The next big step in gravitational-wave science is going to be the construction of next-generation detectors like LISA, CE, and ET. These detectors will detect signals with much higher accuracy, which means the numerical relativity waveforms used to build and calibrate various gravitational-wave models will also need to improve. This thesis is about pushing our code, SpEC, as far as possible to see how accurate we can get, and fixing issues that might prevent us from reaching the accuracy required by the next generation of detectors.
\r\n\r\nIn this thesis, I highlight two improvements made to SpEC with this goal in mind. First, I describe work that makes the black hole spin calculations much faster. The spin calculations were becoming very slow near the merger, when the horizons were highly deformed, and they would only get worse as we increased the resolution of our simulations. The new algorithm is much faster and also opens up paths to future improvements if required. Second, I study various sources of errors in SpEC binary black hole simulations and how to reduce them. We find that relatively targeted changes can improve waveform accuracy by around two orders of magnitude without significantly increasing simulation cost. We also identify some more fundamental limitations that should be considered as we do more high-resolution simulations. Finally, I show preliminary results from an ongoing project demonstrating that, for simple systems, the improvements discussed in this thesis can reach the accuracy required by LISA.
\r\n\r\nTogether, these results show that SpEC can be pushed much further than the current catalog simulations. They also provide a clearer path to producing high-accuracy numerical relativity waveforms needed for LISA and other next-generation gravitational-wave detectors.
", "doi": "10.7907/a7vd-9654", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18712", "collection": "thesis", "collection_id": "18712", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312026-003942225", "primary_object_url": { "basename": "Miller_Simona_2026.pdf", "content": "final", "filesize": 79784307, "license": "other", "mime_type": "application/pdf", "url": "/18712/1/Miller_Simona_2026.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Robustly Measuring the Spins of Binary Black Holes with Gravitational Waves", "author": [ { "family_name": "Miller", "given_name": "Simona Jane", "orcid": "0000-0001-5670-7046", "clpid": "Miller-Simona-Jane" } ], "thesis_advisor": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "thesis_committee": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "McCuller", "given_name": "Lee P.", "orcid": "0000-0003-0851-0593", "clpid": "McCuller-Lee" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "TAPIR" }, { "literal": "div_pma" } ], "abstract": "Over the past decade, the gravitational-wave (GW) detector network of Advanced LIGO, Advanced Virgo, and KAGRA (LVK) has advanced from the first groundbreaking observation of a merging binary black hole (BBH) to the production of a catalog of hundreds of GW signals from the astrophysical population of compact binaries. I focus on the measurement of one fundamental property of black holes: their spin, or intrinsic angular momentum. Spin is a unique probe of astrophysical processes across scales, from fluid dynamics inside stellar cores to the large-scale evolutionary history of our universe, and is the most promising means of disentangling which of the many proposed BBH formation and evolutionary mechanisms dominate the observed population. GWs remain the only way to directly measure black hole spin, yet spin remains poorly constrained: it has a comparatively weak imprint on GW signals, can mimic other physical effects like eccentricity, and is highly susceptible to features in detector noise and systematic uncertainty in waveform models. Without careful safeguards, we risk spurious spin inference and false astrophysical conclusions. To this end, I develop a suite of computational and statistical methods to produce accurate, precise, and unbiased black hole spin inference at every stage of the LVK's data analysis pipeline. To make spin measurements robust in individual BBH detections, I find that we must connect measured parameters with their phenomenology in GW signals. Then, for the astrophysical BBH population, we need to thoroughly test model behavior against simulated populations, understand the role of Monte Carlo uncertainty, and use data-level parameters to probe model misspecification", "doi": "10.7907/tk3k-js43", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18684", "collection": "thesis", "collection_id": "18684", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05292026-034359877", "primary_object_url": { "basename": "Caltech_Thesis.pdf", "content": "final", "filesize": 5620934, "license": "other", "mime_type": "application/pdf", "url": "/18684/1/Caltech_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Toward LISA-Accurate Binary-Black-Hole Waveforms: Waveform Hybridization and Strong-Field Matching", "author": [ { "family_name": "Sun", "given_name": "Dongze", "orcid": "0000-0003-0167-4392", "clpid": "Sun-Dongze" } ], "thesis_advisor": [ { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" } ], "thesis_committee": [ { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The next generation of gravitational-wave detectors will require waveform models that are both substantially longer and substantially more accurate than those used for current ground-based observations. This requirement is especially important for massive binary black holes observed by the Laser Interferometer Space Antenna (LISA), for which signals can remain in band for hundreds to thousands of orbits and can accumulate signal-to-noise ratios large enough that small modeling errors become measurable. At this accuracy, waveform modeling is not only a problem of improving individual approximation schemes. It is also a problem of constructing controlled interfaces between the different descriptions used to model a binary black hole.
\r\n\r\nThis dissertation develops a framework for constructing LISA-accurate binary-black-hole waveforms by connecting post-Newtonian theory, numerical relativity, and black-hole perturbation theory in a consistent way. The first part of the dissertation formulates the LISA-driven accuracy requirements and develops a post-Newtonian--numerical-relativity hybridization framework for producing long waveforms. In this framework, the waveforms are compared at future null infinity after fixing the Bondi--Metzner--Sachs frame, and the intrinsic post-Newtonian parameters are determined as part of the matching procedure rather than assumed to be identical to the quasi-local parameters used to label the numerical-relativity simulation. This construction makes waveform hybridization not only a method for extending waveform duration, but also a diagnostic of asymptotic-frame errors, numerical errors, post-Newtonian truncation errors, and parameter-definition errors.
\r\n\r\nThe second part of the dissertation addresses the parameter-definition problem directly. The masses and spins used in post-Newtonian theory, numerical relativity, and black-hole perturbation theory are physically meaningful within their own constructions, but they are not automatically identical at finite binary separation. To relate these quantities from first principles, this dissertation develops a strong-field matching framework in which black-hole perturbation theory provides the local inner-zone description near each black hole. By constructing gauge-preserving coordinate transformations between local comoving coordinates and the global coordinates used by post-Newtonian theory or numerical relativity, the framework relates point-particle parameters, local black-hole parameters, and quasi-local horizon quantities through the spacetime geometry itself. This provides a route toward parameter maps that can be used in waveform hybridization, numerical-relativity catalogs, and gravitational-wave inference.
\r\n\r\nThe final part of the dissertation develops analytical and numerical infrastructure needed for this program. On the analytical side, the dissertation studies the convergence and regime of validity of high-order post-Newtonian information by comparing successive post-Newtonian truncation orders with a long, high-accuracy numerical-relativity simulation after BMS-frame fixing and parameter fitting. This comparison identifies the velocity range in which higher post-Newtonian orders improve agreement with numerical relativity and the region near merger where the expansion loses quantitative reliability. On the numerical side, the dissertation develops gauge boundary conditions in the Spectral Einstein Code that suppress long-timescale coordinate drift in binary-black-hole simulations, improving the quality of the numerical data needed for precision hybridization and strong-field matching.
\r\n\r\nTogether, these results show that LISA-accurate waveform modeling requires simultaneous control of waveform length, asymptotic frame, intrinsic parameter definitions, post-Newtonian truncation error, and numerical gauge effects. The dissertation therefore provides a framework in which hybridization, strong-field parameter matching, and gauge-controlled numerical relativity become complementary parts of a single program for precision binary-black-hole waveform modeling.
", "doi": "10.7907/ynwh-2a85", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18531", "collection": "thesis", "collection_id": "18531", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05012026-002430480", "primary_object_url": { "basename": "NelliKyle2026Thesis.pdf", "content": "final", "filesize": 9897443, "license": "other", "mime_type": "application/pdf", "url": "/18531/2/NelliKyle2026Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Topics in Numerical Relativity: Horizon Finding, Asynchronous Parallelism, and Cross-Code Comparisons of Gravitational Waveforms", "author": [ { "family_name": "Nelli", "given_name": "Kyle Christopher", "orcid": "0000-0003-2426-8768", "clpid": "Nelli-Kyle-Christopher" } ], "thesis_advisor": [ { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Bouman", "given_name": "Katherine L.", "orcid": "0000-0003-0077-4367", "clpid": "Bouman-K-L" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "From their prediction in 1916 by Einstein, to their first detection almost 100 years later in 2015, gravitational waves provide a new way of looking at the universe, completely separate from electromagnetic radiation. They allow us to probe and study the most extreme gravitational environments that our universe has to offer; black holes. When two black holes merge, they produce a burst of gravitational waves which, if energetic enough, are able to be detected here on earth.
\r\n\r\nHowever, to effectively model these mergers, we cannot solely rely on analytical descriptions. They break down near the actual merger, when spacetime is at its most extreme. To model this merger, we need numerical simulations of mergers to predict what they will look like. These simulations must be extremely accurate due to the incredible precision with which we are able to detect gravitational waves. Therefore, these expensive simulations need to run on supercomputers and be highly efficient in order to meet the necessary accuracy requirements.
\r\n\r\nIn this thesis, we present a novel algorithm for efficiently finding the apparent horizons in numerical simulations done with task-based parallelism. The performance improvement of task-based parallelism over more traditional parallelism is significant, but it introduces considerable algorithmic complexity which had to be dealt with. We then use this novel algorithm to perform the first binary black hole merger done with discontinuous Galerkin methods and analyze the waveform output. Lastly, we present a new feature to the SpECTRE CCE module which allows it to be run on data from other numerical relativity codes. We show this new feature working on simulation data from five different numerical relativity codes.
", "doi": "10.7907/mzc5-hy07", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17445", "collection": "thesis", "collection_id": "17445", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06112025-032822492", "primary_object_url": { "basename": "Senior_Thesis___Correct_Format-1.pdf", "content": "final", "filesize": 7615911, "license": "other", "mime_type": "application/pdf", "url": "/17445/1/Senior_Thesis___Correct_Format-1.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Assembly and Testing of the Spin Dressing Magnet for the Neutron Electric Dipole Experiment", "author": [ { "family_name": "Fox", "given_name": "Jessica Lauren", "orcid": "0000-0001-5053-229X", "clpid": "Fox-Jessica-Lauren" } ], "thesis_advisor": [ { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The discrepancy between the quantity of matter and anitmatter in the universe is something that can likely be attributed to violations in the fundamental symmetries of the universe; however, much like the antimatter itself, there is a discrepancy between the required versus obeserved magnitude of these violations. One theory states that, to account for these violations in symmetry, the neutron must have an electric dipole moment. One such method to find the existence and magnitude of the neutron electric dipole moment (nEDM) is the critical dressing method. Such a method requires the use of two superconducting magnets with perpendicular magnetic fields. This specific method of critical dressing uses superfluid Helium-4, polarized Helium-3, and ultracold polarized neutrons, with critical dressing occurring when the Helium-3 precession rates are equivalent. This method is used to determine the existence of an nEDM, if there is critical dressing with an electric field, there is no nEDM, but if there is a precession rate difference with the electric field, there is an EDM that can thus be measured. Over the past several months, the assembly of the spin dressing magnet used in the critical dressing portion of the nEDM experiment has begun. This has included assembling the boss rings, constructing the magnet frame, placing the story sticks and wire guides, and winding the superconducting wire around the coil skeleton. Data was also taken using this wire. Furthermore, simulations have been run on COMSOL Multiphysics to compare the theoretical predictions with the measurements of the magnetic field and B-field gradients produced by the spin dressing magnet.", "doi": "10.7907/rjne-gy68", "publication_date": "2025", "thesis_type": "senior_major", "thesis_year": "2025" }, { "id": "thesis:17184", "collection": "thesis", "collection_id": "17184", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04292025-174229134", "primary_object_url": { "basename": "Hourihane_Sophie_Thesis-5.pdf", "content": "final", "filesize": 38365146, "license": "other", "mime_type": "application/pdf", "url": "/17184/4/Hourihane_Sophie_Thesis-5.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "A Glitch and the Matrix: Advances in Gravitational-Wave Glitch Mitigation and Acceleration of Pulsar Timing Analyses", "author": [ { "family_name": "Hourihane", "given_name": "Sophie Rose", "orcid": "0000-0002-9152-0719", "clpid": "Hourihane-Sophie-Rose" } ], "thesis_advisor": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "thesis_committee": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Vallisneri", "given_name": "Michele", "orcid": "0000-0002-4162-0033", "clpid": "Vallisneri-M" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "Since the first detection of gravitational-waves in 2015, the field of gravitational-wave astronomy has developed rapidly. Today, there are more than 300 transient gravitational-wave event candidates from stellar-mass sources and we have found evidence for a stochastic background of supermassive black-holes. In this thesis I present work addressing two significant challenges on analyzing these data. The first: mitigating transient, non-Gaussian noise in gravitational-wave detectors, or \"glitches\", that can bias our estimates of physical properties of compact objects. The second: introducing a faster method to analyze pulsar-timing data containing a stochastic background of supermassive black-hole sources. Gravitational-wave astronomy is a data-rich field, and is only becoming more so with upgraded detectors, additional detectors, and longer observing time; we need robust, fast, and unbiased techniques to analyze that data.", "doi": "10.7907/q6k7-hv53", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17330", "collection": "thesis", "collection_id": "17330", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312025-230908742", "primary_object_url": { "basename": "udall_rhiannon_2025.pdf", "content": "final", "filesize": 8288274, "license": "other", "mime_type": "application/pdf", "url": "/17330/1/udall_rhiannon_2025.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Robust Gravitational Wave Analysis at the Catalog Scale", "author": [ { "family_name": "Udall", "given_name": "Rhiannon Pollard", "orcid": "0000-0001-6877-3278", "clpid": "Udall-Rhiannon-P" } ], "thesis_advisor": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Reitze", "given_name": "David H.", "orcid": "0000-0002-5756-1111", "clpid": "Reitze-D-H" }, { "family_name": "McCuller", "given_name": "Lee P.", "orcid": "0000-0003-0851-0593", "clpid": "McCuller-Lee" }, { "family_name": "Hallinan", "given_name": "Gregg W.", "orcid": "0000-0002-7083-4049", "clpid": "Hallinan-G-W" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "The rapid improvement in the sensitivity of ground based gravitational wave detectors has produced a huge variety of technical insights, but has also brought new challenges in gravitational wave data analysis. In this dissertation I address two of those challenges: the rapid increase in the number of detected events, and the need for robust astrophysical inferences in the presence of transient detector glitches. To manage the number of gravitational wave transients now regularly detected, I developed infrastructure for the LIGO-Virgo-KAGRA collaboration which monitors and collates the results of many disparate analyses in order to produce the final transient catalog. I implemented physically informed models for scattered light glitches into standard parameter estimation tools, and so that the potential realizations of these glitches can be marginalized over when performing astrophysical inference. This method was used to better understand GW191109, an event from the third observing run with potentially dynamical formation history. These tools were also applied to better understand the behavior of parameter estimation in the presence of glitches, and to search for statistical tests which can identify if parameter estimation is biased by the presence of a glitch.", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17341", "collection": "thesis", "collection_id": "17341", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06012025-190154036", "primary_object_url": { "basename": "Golomb-full thesis-main.pdf", "content": "final", "filesize": 29138127, "license": "other", "mime_type": "application/pdf", "url": "/17341/7/Golomb-full thesis-main.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Probing Astrophysics, Cosmology, and Nuclear Physics with Gravitational Waves from Black Holes and Neutron Stars", "author": [ { "family_name": "Golomb", "given_name": "Jacob Matthew", "orcid": "0000-0002-6977-670X", "clpid": "Golomb-Jacob-Matthew" } ], "thesis_advisor": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Vallisneri", "given_name": "Michele", "orcid": "0000-0002-4162-0033", "clpid": "Vallisneri-Michele" }, { "family_name": "El-Badry", "given_name": "Kareem J.", "orcid": "0000-0002-6871-1752", "clpid": "El-Badry-K-J" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "Gravitational waves now serve as a powerful tool for studying physics of compact objects, including black holes and neutron stars. \r\nWhen two compact objects merge, they emit gravitational waves that encode information about their masses, spins, and orbital dynamics. \r\nGround-based detectors capture these signals, allowing us not only to measure the properties of individual mergers but also to characterize the population properties of black holes and neutron stars. In this thesis, I present a collection of works using real and simulated gravitational wave observations of compact binary coalescences to study the physics of black holes and neutron stars, and the implications these observations have on our broader understanding of astrophysics and fundamental physics.
\r\n \r\nThe first part of this thesis is background material reviewing some of the theory behind gravitational waves. The second part focuses on measuring the physical properties of a compact binary coalescence detected in gravitational wave data. This includes the methods and models used in parameter estimation and a presentation of the properties of detections in the fourth Gravitational Wave Transient Catalog (GWTC-4). The third part of this thesis turns to measuring and extracting astrophysical information from the population properties of compact binaries. This features the astrophysical distributions of binary black holes as inferred from GWTC-3 and GWTC-4. I also present studies measuring specific aspects of the binary black hole mass and spin distributions, and the implications these results have for understanding binary black hole formation channels and stellar astrophysics. This section additionally features applications of population inference to studies of large-scale structure and predictions for the gravitational wave stochastic background, as well as technical discussions of the methods and custom libraries used to implement population analyses and potential biases associated with commonly-used methods. The fourth part explores how properties of dense nuclear matter are encoded in observations of neutron stars. This section includes studies using our knowledge of the nuclear equation of state to classify low-mass compact binary mergers, and results from using gravitational waves and electromagnetic observations of neutron stars to measure the equation of state and neutron star population properties.
", "doi": "10.7907/txde-0h55", "publication_date": "2025-06", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17364", "collection": "thesis", "collection_id": "17364", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-165440282", "primary_object_url": { "basename": "thesis_submission_Legred_2025_final.pdf", "content": "final", "filesize": 23001365, "license": "other", "mime_type": "application/pdf", "url": "/17364/1/thesis_submission_Legred_2025_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Neutron Stars: Robust Constraints on Dense Matter from Astrophysics", "author": [ { "family_name": "Legred", "given_name": "Isaac Norman", "orcid": "0000-0002-9523-9617", "clpid": "Legred-Isaac-Norman" } ], "thesis_advisor": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "thesis_committee": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Kasliwal", "given_name": "Mansi M.", "orcid": "0000-0002-5619-4938", "clpid": "Kasliwal-Mansi-M" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "TAPIR" }, { "literal": "div_pma" } ], "abstract": "Neutron stars are exceptional astrophysical objects, harboring likely the densest matter in the universe outside of black holes.
\r\n \r\nHowever, uncertainty in the properties of matter at the densities achieved inside of neutron stars means that the structure of neutron stars cannot be fully understood from first principles.
\r\n \r\nModern statistical and computational tools however, along with cutting-edge observational strategies have enabled the properties of neutron stars to be constrained using astrophysical data.
\r\n \r\nIn this thesis, I will discuss work I have carried out examining what can be learned about neutron stars, and the dense matter inside of them, using electromagnetic and gravitational-wave observations of neutron stars.
\r\n \r\nIn particular, I will discuss constraints on nonparametric models of the dense-matter equation of state, and why nonparametric models are an effective strategy for faithfully representing uncertainty.
\r\n \r\nI will also discuss the interplay between understanding the astrophysical channels for forming neutron stars, and the neutron-star matter equation of state, including how we can use our understanding of dense matter to classify objects.
\r\n \r\nFinally, I will discuss some considerations for simulating astrophysical neutron stars, which is necessary in order to interpret the full range of astrophysical observations of merging neutron stars, such as the neutron star merger GW170817.
", "doi": "10.7907/fzdw-w868", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17372", "collection": "thesis", "collection_id": "17372", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-193721130", "primary_object_url": { "basename": "habib_sarah_2025.pdf", "content": "final", "filesize": 1447710, "license": "other", "mime_type": "application/pdf", "url": "/17372/1/habib_sarah_2025.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Error Quantification and Mitigation for Numerical Compact Binary Waveforms", "author": [ { "family_name": "Habib", "given_name": "Sarah Mary", "orcid": "0000-0002-4725-4978", "clpid": "Habib-Sarah-Mary" } ], "thesis_advisor": [ { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" }, { "family_name": "Most", "given_name": "Elias R.", "orcid": "0000-0002-0491-1210", "clpid": "Most-E-R" } ], "thesis_committee": [ { "family_name": "Most", "given_name": "Elias R.", "orcid": "0000-0002-0491-1210", "clpid": "Most-E-R" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Gravitational wave analysis requires waveform models to compare with observed signals from compact binaries. These models are based on and validated by numerical relativity waveforms---waveforms output from codes developed to numerically evolve the Einstein field equations. The efficacy of numerical waveforms for analysis is limited by error from both numerical and astrophysical sources. This thesis makes two contributions to the quantification and mitigation of this error.
\r\n\r\nChapter 2 describes a new algorithm for eccentricity reduction, the process of determining initial conditions for quasicircular binary orbits. This iterative procedure requires a measurement of eccentricity based on an early-inspiral trajectory. We find that the use of nonlinear fitting techniques such as variable projection leads to vastly improved consistency in eccentricity measurements.
\r\n\r\nFinally, Chapter 3 presents an in-depth quantification of error in numerical binary neutron star waveforms from three vastly different numerical relativity codes. We find that overall these codes produce consistent binary neutron star evolutions, but that further accuracy improvements will be required for analysis of next-generation gravitational wave detector signals.
", "doi": "10.7907/jbre-7e68", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17398", "collection": "thesis", "collection_id": "17398", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032025-041244872", "primary_object_url": { "basename": "brian_seymour_2025.pdf", "content": "final", "filesize": 12247520, "license": "other", "mime_type": "application/pdf", "url": "/17398/1/brian_seymour_2025.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Future Prospects in Gravitational Waves: From Testing\r\nFundamental Physics to Instruments beyond LIGO", "author": [ { "family_name": "Seymour", "given_name": "Brian Christopher", "orcid": "0000-0002-7865-1052", "clpid": "Seymour-Brian-Christopher" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Zurek", "given_name": "Kathryn M.", "orcid": "0000-0002-2629-337X", "clpid": "Zurek-K-M" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "In this thesis, we study the prospects for gravitational wave astronomy in the future. We focus on a couple of areas for gravitation waves beyond LIGO: improving measurement techniques of cosmological parameters, developing new waveforms for environmental effects, probing fundamental physics in waveforms, and high frequency gravitational wave detectors.
\r\n\r\nIn the first part of this thesis, we develop two methods to constrain cosmological parameters using gravitational-wave observations. The first approach employs the statistical dark siren method, where the observed distribution of binary black hole events---whose luminosity distances are directly measured---is matched against astrophysical population models. By analyzing the Fisher information in the event distribution, we derive the Cram\\'er-Rao bounds to quantify both statistical uncertainties and potential biases arising from unmodeled features in the merger rate and mass distribution. The second approach leverages the benefits of multiband observations with decihertz detectors, which dramatically improve host galaxy identification by refining source localization. This enhanced capability benefits reduces systematic errors in the measurement of the Hubble constant and other cosmological parameters. Together, these methods pave new pathways for precision cosmography using gravitational waves.
\r\n\r\nIn the second part of the thesis, we investigate gravitational-wave signatures arising from binary black holes merging in the vicinity of supermassive black holes (SMBHs). One study focuses on hierarchical triple systems where the orbital motion around an SMBH imprints striking modulations on the gravitational waveforms. In our work, gravitational lensing is highlighted as a pivotal effect---alongside Doppler shifts and de Sitter precession---that is crucial for breaking parameter degeneracies. A complementary analysis considers eccentric orbits, incorporating orbital pericenter precession alongside Doppler and precession effects to further refine parameter estimation. Together, these investigations demonstrate that dynamic lensing and orbital modulations can be leveraged to probe SMBH properties and their environments with unprecedented precision, underscoring the importance of incorporating these environmental effects into waveform models.
\r\n\r\nIn the third work, we explore inspiral tests of general relativity by examining the phase evolution of gravitational-wave signals from coalescing binary systems. First, we test Giddings' non-violent non-locality proposal, which posits that quantum information is transferred via a non-local interaction that generates metric perturbations around black holes by creating an effective-one-body waveform. We show that this can be captured by parameterized tests of general relativity waveforms. In the second half, we assess the robustness of post-Newtonian coefficients against unmodeled deviations by introducing parameterized tests that exploit the inherent geometry of the waveform. We show that the tests of general relativity are intimately related to the geometry of the signal manifold and propose a new singular value decomposition method to search for deviations for testing the predictions of general relativity and probing potential modifications to gravitational dynamics.
\r\n\r\nIn the fourth part of this thesis, we explore optimizing the GEO600 detector for high-frequency gravitational wave detection. Although GEO600 is less sensitive than LIGO in the conventional 50\u2013400 Hz band, we demonstrate that by detuning the signal-recycling mirror its sensitivity can be enhanced at tens of kHz. Using simulations with Finesse 3.0, we show that the sensitive point can be effectively scanned across various frequencies by adjusting the detuning angle. This tuning enables GEO600 to better target monochromatic sources, such as boson clouds arising from superradiance, thereby opening a promising new window for high-frequency gravitational wave astronomy.
", "doi": "10.7907/ask9-zk26", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16172", "collection": "thesis", "collection_id": "16172", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08312023-190727801", "primary_object_url": { "basename": "Lo_KaLok(Rico)_2024.pdf", "content": "final", "filesize": 9876002, "license": "other", "mime_type": "application/pdf", "url": "/16172/1/Lo_KaLok(Rico)_2024.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Gravitational Wave Exotica - Advancing the Search for Signatures of Exotic Compact Objects and Gravitational Lensing from Data-Analysis and Theoretical Perspectives", "author": [ { "family_name": "Lo", "given_name": "Ka Lok (Rico)", "orcid": "0000-0003-1561-6716", "clpid": "Lo-Ka-Lok-Rico" } ], "thesis_advisor": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "thesis_committee": [ { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Fuller", "given_name": "James", "orcid": "0000-0002-4544-0750", "clpid": "Fuller-J" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "In this thesis, I explore two new arenas of gravitational-wave physics and advance them from both data-analysis and theoretical perspectives. I probe the nature of the remnant of a compact binary merger and study the strong gravitational lensing of gravitational waves. For probing the nature of a merger remnant, I first describe recipes of computing radiation emitted by a perturbed Kerr black hole, and in particular using the Generalized Sasaki-Nakamura formalism. Using a modified Kerr black hole spacetime as a model of a generic compact object, I then describe a prescription to compute waveforms of the repeating bursts of gravitational waves, referred to as gravitational-wave echoes, that are theorized to be emitted when a compact object with a reflective surface is formed as the remnant of a merger. Equipped with a waveform model for these echoes, I present a Bayesian model selection approach to look for echoes in data while inferring properties of the potential exotic compact object. I apply this approach to search for echoes in the data covering the first, the second, and the first half of the third observing run of the LIGO-Virgo-KAGRA network. For the strong lensing of gravitational waves, I first develop a Bayesian statistical framework that is capable of computing the probability of a given set of gravitational-wave events being the strongly-lensed counterparts of the same source or simply coming from distinct sources. If they are truly lensed, the framework can also infer the properties of the lensed source in a way unaffected by lensing. I apply this framework to search for signatures of strongly-lensed binary black hole systems in the data covering the third observing run. While we did not find any statistically significant evidence in the search for gravitational-wave echoes and strongly-lensed binary black holes, we can still place limits using the null results. Admittedly the existence of exotic compact objects is speculative and the observing rate of strongly-lensed gravitational waves is rare; however, the scientific impacts that they can bring are profound if they are proven to exist.", "doi": "10.7907/gycj-ch63", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16408", "collection": "thesis", "collection_id": "16408", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05222024-171910928", "primary_object_url": { "basename": "Mitman_Keefe_2024_Thesis.pdf", "content": "final", "filesize": 6423986, "license": "other", "mime_type": "application/pdf", "url": "/16408/1/Mitman_Keefe_2024_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Asymptotics with Numerical Relativity: Gravitational Memory, BMS Frames, and Nonlinearities", "author": [ { "family_name": "Mitman", "given_name": "Keefe Edward Alden", "orcid": "0000-0003-0276-3856", "clpid": "Mitman-Keefe-Edward-Alden" } ], "thesis_advisor": [ { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Teukolsky", "given_name": "Saul A.", "orcid": "0000-0001-9765-4526", "clpid": "Teukolsky-S-A" }, { "family_name": "Scheel", "given_name": "Mark", "orcid": "0000-0001-6656-9134", "clpid": "Scheel-M-A" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "With the recent commencement of the LIGO-Virgo-KAGRA (LVK) Collaboration's fourth observing run, the field of gravitational-wave physics is uniquely poised to collect even more accurate data from compact binary coalescences. Consequently, we will soon be able to perform more stringent tests of general relativity (GR). Because GR must, in some regime, be violated---either because the Universe is described by an alternative theory or because of the emergence of quantum effects---these tests of GR are crucial for unveiling new physics. Performing such tests, however, requires that our understanding of GR and gravitational waves is reliable. And, while there are many tools for unraveling Einstein's equations, the only one that is robust in every regime of GR is numerical relativity (NR): a means for computing accurate solutions to Einstein's equations with supercomputers.
\r\n \r\nIn this thesis, I highlight some recent and impactful advancements that have been incorporated into NR simulations of binary black holes. In particular, I show how a more robust procedure for calculating the radiative data at future null infinity from NR simulations, called Cauchy-characteristic evolution (CCE), produces waveforms that exhibit a not-yet observed prediction of GR colloquially referred to as memory. This phenomenon corresponds to the permanent net displacement that two observers will experience due to the passage of transient gravitational radiation. Memory is of particular interest in the testing GR and theory communities because of its relation to asymptotic symmetries and scattering amplitude calculations in particle physics. With these contemporary CCE waveforms, I provide explicit methods to calculate the various memory effects and I also comment on their relative magnitudes and detectability in the near future. Apart from this, I also demonstrate the importance of controlling the BMS freedoms of these waveforms, i.e., their frame freedom at future null infinity, for building waveform models as well as for extracting physics, such as GR's nonlinearities, from the ringdown phase of binary black hole mergers.
\r\n \r\nAs we start to enter the next phase of high-precision gravitational-wave astronomy, correctly modeling gravitational waves with NR simulations will play a crucial role in pushing Einstein's theory of relativity to its limits. It is the aim of this thesis to illustrate the importance of combining gravitational-wave theory and NR to not only improve our understanding of black holes and gravitational waves, but also further our prospects for unveiling the true nature of gravity within our universe.
", "doi": "10.7907/7akc-yg91", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16424", "collection": "thesis", "collection_id": "16424", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05242024-202843732", "primary_object_url": { "basename": "Alvin_Li_Thesis.pdf", "content": "final", "filesize": 20313963, "license": "other", "mime_type": "application/pdf", "url": "/16424/1/Alvin_Li_Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Probing the Higher Redshift Universe by Studying Strong Lensing of Gravitational Waves and Enhancing Search Sensitivity of the GstLAL Search Pipeline", "author": [ { "family_name": "Li", "given_name": "Ka Yue Alvin", "orcid": "0000-0001-6728-6523", "clpid": "Li-Ka-Yue-Alvin" } ], "thesis_advisor": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Fuller", "given_name": "James", "orcid": "0000-0002-4544-0750", "clpid": "Fuller-J" }, { "family_name": "Ravi", "given_name": "Vikram", "orcid": "0000-0002-7252-5485", "clpid": "Ravi-Vikram" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "The LIGO-Virgo-KAGRA (LVK) collaboration first observed gravitational waves in 2015, and more than $90$ gravitational-wave events have been observed, all coming from mergers of compact objects (black holes and neutron stars), known as compact binary coalescences (CBC). Studying and observing gravitational waves opens a new window for us to understand the nature of spacetime and the universe. Strain data from LVK's detectors are analyzed by search pipelines to identify weak gravitational-wave signals in noisy data. To maximize the potential of gravitational waves, it is essential to continue to improve search pipelines' sensitivity to probe GW sources with the broadest range of parameters and from the furthest distances. I will give a detailed overview of the GstLAL pipeline and present related development (ongoing) work for GstLAL to enhance its search effectiveness and efficiency.
\r\n\r\nIn the second part of my thesis, I will focus on gravitational lensing of gravitational waves. As masses can produce curvature in spacetime, gravitational waves, like electromagnetic (EM) waves, are deflected when passing by massive intervening objects before reaching gravitational-wave detectors on Earth, an effect known as gravitational lensing. Observing lensed gravitational waves confirms another prediction in Einstein's general relativity and enables us to conduct cosmography studies, test general relativity, search for dark matter and other exotic phenomena, and deepen our understanding of the universe. I will give a detailed introduction to gravitational lensing of gravitational waves. We then introduce a Targeted subthreshold search for strongly-lensed gravitational wave pipeline called \"TESLA\". The TESLA pipeline is the flagship to look for sub-threshold lensed gravitational waves. Next, we present the results of the LVK collaboration-wide effort to search for lensing signatures in gravitational-wave data from the third observing run O3. Next, we introduce a significant update to the TESLA pipeline, now known as the TESLA-X pipeline, with enhanced search sensitivity towards lensed gravitational waves. We also introduce an alternative ranking statistic implemented into the TESLA-X pipeline that considers the signal's consistency with the assumed lens model. Finally, we end the thesis with a summary and an outline of possible future work.
", "doi": "10.7907/hc11-h960", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16445", "collection": "thesis", "collection_id": "16445", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302024-045951995", "primary_object_url": { "basename": "Wang_Yijun_thesis_final.pdf", "content": "final", "filesize": 8611097, "license": "other", "mime_type": "application/pdf", "url": "/16445/1/Wang_Yijun_thesis_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Topics in Gravitational Wave Physics: Lensing, Detection with Astrometry and Dark Siren Hubble Measurement", "author": [ { "family_name": "Wang", "given_name": "Yijun", "orcid": "0000-0002-5581-2001", "clpid": "Wang-Yijun" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Dor\u00e9", "given_name": "Olivier P.", "orcid": "0000-0001-7432-2932", "clpid": "Dor\u00e9-O" }, { "family_name": "Chang", "given_name": "Tzu-Ching", "orcid": "0000-0001-5929-4187", "clpid": "Chang-Tzu-Ching" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Chang", "given_name": "Tzu-Ching", "orcid": "0000-0001-5929-4187", "clpid": "Chang-Tzu-Ching" }, { "family_name": "Dor\u00e9", "given_name": "Olivier P.", "orcid": "0000-0001-7432-2932", "clpid": "Dor\u00e9-O" }, { "family_name": "Adhikari", "given_name": "Rana", "orcid": "0000-0002-5731-5076", "clpid": "Adhikari-R" }, { "family_name": "Pardo", "given_name": "Kris", "orcid": "0000-0002-9910-6782", "clpid": "Pardo-Kris" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "div_pma" } ], "abstract": "In this thesis, we study several subjects in gravitational wave (GW) physics, including gravitational wave lensing, detection with astrometry data and dark siren measurement of cosmological parameters.
\r\n\r\nWe investigate various lensing features and their detection prospects in third-generation gravitational-wave networks. Firstly, we focus on type II lensed images which are Hilbert transforms of regular images. We compute the waveform mismatch and quantify the distinguishable fraction given Bayes factor thresholds over a range of binary mass ratio and redshifted mass. We make forecast on the detectable and distinguishable type II images in aLIGO Voyager, Cosmic Explorer and Einstein Telescope. This work shows that a significant number of type II images can be distinguished from waveforms alone, and this strategy can contribute to future pipelines for more accurate GW event inference.
\r\n\r\nWe further model relativistic lensing in a large-inclination hierarchical triple system with a central Kerr supermassive black hole. We combine the elliptical integral formalism and optical scalar formalism to study image location and magnification. By analyzing the repeated lensing signature observed by the Decihertz Gravitational-wave Observatory, we examine the importance of relativistic images in detecting the presence of lensing or specifically the lens spin. We compute the detectable effective volume and estimate the upper limit for expected number of such events. This work demonstrates that lensing with relativistic images is a fruitful avenue where decihertz observation contributes to studies on intermediate-mass binary black holes and their galactic environment.
\r\n\r\nGW detection with astrometry was proposed as an alternative strategy that uses stellar astrometry data for GW measurement with flexible frequency coverage. We point out that surveys providing relative astrometry only can also be sensitive to GWs. We apply this method to the Roman Space Telescope Galactic Bulge Time Domain survey and make sensitivity forecast for both monochromatic GWs from supermassive binary black holes and stochastic GW background. We clarify the survey requirements and technical challenges for GW detection, and show that Roman will enable microhertz GW measurement for local sources. We also present on-going work to develop a data-processing pipeline to use Kepler archival data to search for GWs.
\r\n\r\nWith increasing number of events in GW catalog, the GW source population offers a unique perspective into cosmology and astrophysics. In the last chapter, we use a Fisher information formalism to quantify the astrophysical model error tolerance of GW dark siren measurement on cosmological parameters. We generate galaxy catalog based on realistic survey and population parameters, and we apply expected GW uncertainties in third-generation ground-based networks. Based on simulation results, we study dominating error factors and make suggestions to dark siren selection strategy given different total error requirements.
", "doi": "10.7907/fjya-qm21", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:16502", "collection": "thesis", "collection_id": "16502", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06042024-064008692", "primary_object_url": { "basename": "Shreya_Anand_Caltech_Thesis.pdf", "content": "final", "filesize": 22034472, "license": "other", "mime_type": "application/pdf", "url": "/16502/1/Shreya_Anand_Caltech_Thesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Cosmic Gold Mining: Hunting for the Astrophysical Sites of r-Process Nucleosynthesis", "author": [ { "family_name": "Anand", "given_name": "Shreya", "orcid": "0000-0003-3768-7515", "clpid": "Anand-Shreya" } ], "thesis_advisor": [ { "family_name": "Kasliwal", "given_name": "Mansi M.", "orcid": "0000-0002-5619-4938", "clpid": "Kasliwal-Mansi-M" } ], "thesis_committee": [ { "family_name": "Fuller", "given_name": "James", "orcid": "0000-0002-4544-0750", "clpid": "Fuller-J" }, { "family_name": "Mawet", "given_name": "Dimitri", "orcid": "0000-0002-8895-4735", "clpid": "Mawet-D" }, { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Kasliwal", "given_name": "Mansi M.", "orcid": "0000-0002-5619-4938", "clpid": "Kasliwal-Mansi-M" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "Zwicky Transient Facility" }, { "literal": "div_pma" } ], "abstract": "One of the major open questions in astronomy is where the heaviest elements in the Universe are formed. These elements, generated via the rapid neutron-capture process (r-process), require environments abundant with free neutrons, present only in extreme cosmic explosions, which are by nature inherently rare. To date, vivid, direct evidence of heavy element nucleosynthesis has been seen and most extensively studied in the binary neutron star (BNS) merger GW170817. However, neutron star\u2013black hole (NSBH) mergers, some collapsing massive stars (collapsars), and other explosions have also been proposed as alternative sites of r-process production. This thesis explores BNS mergers, NSBH mergers, and collapsars as r-process sites through observational studies. In this work, we first investigate whether r-process signatures are present in the light curves of broadlined type Ic supernovae (SNe Ic-BL) associated with long-duration gamma-ray bursts. For this study, we conduct optical imaging with the Zwicky Transient Facility (ZTF) and near-infrared imaging with the Wide-Field Infrared Camera on the Palomar 200-in Hale telescope of ZTF-discovered SNe Ic-BL. Second, we study the chemical distribution of ejecta in the kilonova (KN)---an optical/near-infrared transient powered by the radioactive decay of r-process elements---counterpart to GW170817, using new state-of-the-art KN models and incorporating precise inclination information on GW170817 into our inference. Third, we describe systematic searches conducted with ZTF for KNe associated with both BNS and NSBH mergers detected by the LIGO Virgo KAGRA detector network during its third and fourth observing runs. Based on our non-detections, we place constraints on the properties of KNe from both BNS and NSBH merger sites. Finally, we summarize the unique insights we have gained on the nature of r-process sites from observations and non-detections. We also discuss prospects for discovering and characterizing these transients with upcoming surveys such as the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope.", "doi": "10.7907/145k-w841", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:15230", "collection": "thesis", "collection_id": "15230", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-084739008", "type": "thesis", "title": "A Deep Dive into the Connections Between the Renormalization Group and Deep Learning in the Ising Model", "author": [ { "family_name": "Taylor", "given_name": "Kelsie", "orcid": "0009-0001-7510-2306", "clpid": "Taylor-Kelsie-Reed" } ], "thesis_advisor": [ { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" }, { "family_name": "Lykken", "given_name": "Joseph", "orcid": "0000-0002-0090-9439", "clpid": "Lykken-J" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The renormalization group (RG) is an essential technique in statistical physics and quantum field theory, which considers scale-invariant properties of physical theories and how these theories\u2019 parameters change with scaling. Deep learning is a powerful computational technique that uses multi-layered neural networks to solve a myriad of complicated problems. Previous research suggests the possibility that unsupervised deep learning may be a form of RG flow, by being a layer-by-layer coarse graining of the original data. We examined this connection on a more rigorous basis for the simple example of Kadanoff block renormalization of the 2D nearest-neighbor Ising model, with our deep learning accomplished via Restricted Boltzmann Machines (RBMs). We developed extensive renormalization techniques for the 1D and 2D Ising model to provide a baseline for comparison. For the 1D Ising model, we successfully used Adam optimization on a correlation length loss function to learn the group flow; yielding results consistent with the analytical model for infinite N. For the 2D Ising model, we successfully generated Ising model samples using the Wolff algorithm, and performed the group flow using a quasi-deterministic method, validating these results by calculating the critical exponent \\nu. We then examined RBM learning of the Ising model layer by layer, finding a blocking structure in the learning that is qualitatively similar to RG. Lastly, we directly compared the weights of each layer from the learning to Ising spin renormalization, but found quantitative inconsistencies for the simple case of nearest-neighbor Ising models.", "doi": "10.7907/ztpg-z092", "publication_date": "2023", "thesis_type": "senior_major", "thesis_year": "2023" }, { "id": "thesis:15230", "collection": "thesis", "collection_id": "15230", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-084739008", "type": "thesis", "title": "A Deep Dive into the Connections Between the Renormalization Group and Deep Learning in the Ising Model", "author": [ { "family_name": "Taylor", "given_name": "Kelsie", "orcid": "0009-0001-7510-2306", "clpid": "Taylor-Kelsie-Reed" } ], "thesis_advisor": [ { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" }, { "family_name": "Lykken", "given_name": "Joseph", "orcid": "0000-0002-0090-9439", "clpid": "Lykken-J" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Politzer", "given_name": "Hugh David", "orcid": "0000-0002-4983-6621", "clpid": "Politzer-H-D" }, { "family_name": "Alicea", "given_name": "Jason F.", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Filippone", "given_name": "Bradley W.", "orcid": "0000-0002-2618-2688", "clpid": "Filippone-B-W" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Hutzler", "given_name": "Nicholas R.", "orcid": "0000-0002-5203-3635", "clpid": "Hutzler-N-R" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Spiropulu", "given_name": "Maria", "orcid": "0000-0001-8172-7081", "clpid": "Spiropulu-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The renormalization group (RG) is an essential technique in statistical physics and quantum field theory, which considers scale-invariant properties of physical theories and how these theories\u2019 parameters change with scaling. Deep learning is a powerful computational technique that uses multi-layered neural networks to solve a myriad of complicated problems. Previous research suggests the possibility that unsupervised deep learning may be a form of RG flow, by being a layer-by-layer coarse graining of the original data. We examined this connection on a more rigorous basis for the simple example of Kadanoff block renormalization of the 2D nearest-neighbor Ising model, with our deep learning accomplished via Restricted Boltzmann Machines (RBMs). We developed extensive renormalization techniques for the 1D and 2D Ising model to provide a baseline for comparison. For the 1D Ising model, we successfully used Adam optimization on a correlation length loss function to learn the group flow; yielding results consistent with the analytical model for infinite N. For the 2D Ising model, we successfully generated Ising model samples using the Wolff algorithm, and performed the group flow using a quasi-deterministic method, validating these results by calculating the critical exponent \\nu. We then examined RBM learning of the Ising model layer by layer, finding a blocking structure in the learning that is qualitatively similar to RG. Lastly, we directly compared the weights of each layer from the learning to Ising spin renormalization, but found quantitative inconsistencies for the simple case of nearest-neighbor Ising models.", "doi": "10.7907/ztpg-z092", "publication_date": "2023", "thesis_type": "senior_major", "thesis_year": "2023" }, { "id": "thesis:15128", "collection": "thesis", "collection_id": "15128", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04042023-210926442", "primary_object_url": { "basename": "DongDillon_Caltech_PhD_thesis_final.pdf", "content": "final", "filesize": 7437155, "license": "other", "mime_type": "application/pdf", "url": "/15128/1/DongDillon_Caltech_PhD_thesis_final.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Shocks, Jets, and Emerging Nebulae: Direct Detection and Characterization of Extragalactic Radio Transients in the VLA Sky Survey", "author": [ { "family_name": "Dong", "given_name": "Dillon Zhejun", "orcid": "0000-0001-9584-2531", "clpid": "Dong-Dillon-Zhejun" } ], "thesis_advisor": [ { "family_name": "Hallinan", "given_name": "Gregg W.", "orcid": "0000-0002-7083-4049", "clpid": "Hallinan-G-W" } ], "thesis_committee": [ { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "Ravi", "given_name": "Vikram", "orcid": "0000-0002-7252-5485", "clpid": "Ravi-Vikram" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" }, { "family_name": "Fuller", "given_name": "James", "orcid": "0000-0002-4544-0750", "clpid": "Fuller-J" }, { "family_name": "Hallinan", "given_name": "Gregg W.", "orcid": "0000-0002-7083-4049", "clpid": "Hallinan-G-W" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "For most of their lives, massive stars and supermassive black holes evolve steadily, changing only gradually on human timescales. But on occasion, these cosmic engines erupt, lighting up their surroundings like flashes in the dark. Under the right conditions, the eruptions can manifest as slow radio transients, rising and fading on timescales of weeks to decades. By finding these transients and observing their evolution, we can study otherwise inaccessible aspects of the engines' lives, and piece together their influence on their surroundings.
\r\n\r\nUntil recently, most of our knowledge of slow radio transients came from follow-up observations of explosions first discovered as optical and high-energy transients. This avenue of discovery, while illuminating, provides an indelibly incomplete picture of the radio transient landscape. Moreover, each successful follow-up detection typically comes at the cost of many unsuccessful attempts (measured in both telescope and human time).
\r\n\r\nMy thesis helps address these issues by finding and characterizing transients directly in radio surveys. By applying novel transient detection techniques to data from the Very Large Array Sky Survey (VLASS), I produced the first uniformly selected sample of radio transients associated with local universe galaxies. The 64 transients in my sample have roughly doubled the total number of directly detected slow radio transients in the literature. This sample has enabled the first volume-limited characterization of the demographics of extragalactic slow radio transients. It has also facilitated the discovery of two previously unseen transient types: the merger of a compact object with a massive star and a decades-old emerging pulsar wind nebula.
\r\n\r\nThese early results used only ~15% of the currently available data from VLASS and focused only on extragalactic transients at low redshift. By applying the same techniques to the full survey, I have found ~2000 new transients, increasing the number of known slow radio transients (detected by any means) by a further order of magnitude. With this new sample, my collaborators and I are beginning to shift the study of slow radio transients from the domain of single-object deep-dives to the domain of statistical samples.
", "doi": "10.7907/xwy9-tc17", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:15051", "collection": "thesis", "collection_id": "15051", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11022022-054918241", "primary_object_url": { "basename": "XiangLi_thesis1113.pdf", "content": "final", "filesize": 20986255, "license": "other", "mime_type": "application/pdf", "url": "/15051/1/XiangLi_thesis1113.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Topics in Gravitational Wave Physics: Quantum Theory for Detector Improvement and High-Precision Modeling of Binary Black Hole Ringdown Waveform", "author": [ { "family_name": "Li", "given_name": "Xiang", "orcid": "0000-0002-3780-7735", "clpid": "Li-Xiang" } ], "thesis_advisor": [ { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" } ], "thesis_committee": [ { "family_name": "Weinstein", "given_name": "Alan Jay", "orcid": "0000-0002-0928-6784", "clpid": "Weinstein-Alan-J-Physics" }, { "family_name": "Chen", "given_name": "Yanbei", "orcid": "0000-0002-9730-9463", "clpid": "Chen-Yanbei" }, { "family_name": "Chatziioannou", "given_name": "Katerina", "orcid": "0000-0002-5833-413X", "clpid": "Chatziioannou-K" }, { "family_name": "McCuller", "given_name": "Lee P.", "orcid": "0000-0003-0851-0593", "clpid": "McCuller-Lee" } ], "local_group": [ { "literal": "LIGO" }, { "literal": "div_pma" } ], "abstract": "This thesis covers topics in gravitational wave physics, including optomechanical measurement theory, novel detection schemes (PT-symmetric interferometer, matter-wave interferometer), and modeling of binary black hole ringdown waveform.
\r\n\r\nMeasurements are accomplished through the interaction between signal and measurement devices. Identifying the nature of couplings is an important step in designing setups for specific applications. In Chapter II, we develop a general framework based on the system Hamiltonian to unambiguously classify optomechanical couplings. We add the new type, ``coherent coupling'', where the mechanical oscillation couples several non-degenerate optical modes supported in the cavity. We give examples of different couplings, discuss in detail one particular case of the coherent coupling, and demonstrate its benefits in optomechanical experiments. Our general framework allows the design of optomechanical systems in a methodological way, to precisely exploit the strengths of some particular optomechanical couplings.
\r\n\r\nConventional resonant detectors are subject to bandwidth-peak sensitivity trade-off, which can be traced back to the quantum Cramer-Rao Bound. Chapters III and IV in this thesis are devoted to the study of PT-symmetric amplifier, which is a stable quantum amplification scheme enabled by two-mode non-degenerate parametric amplification. In Chapter III, we study stability and sensitivity improvements for laser-interferometric gravitational-wave detectors and microwave cavity axion detectors, under Hamiltonian formalism adopting single-mode and resolved-sideband approximations. In Chapter IV, we go beyond these approximations and consider realistic parameters in the optomechanical realization of PT-symmetric interferometer for gravitational detection. We show that the main conclusion concerning stability remains intact using Nyquist analysis and a detailed time-domain simulation.
\r\n\r\nThe detection method of gravitational waves is developed with linear quantum measurement theory. In Chapter V, we extend the usage of this theory to another kind of measurement device \u2014 matter-wave interferometers, which have been widely discussed as an important platform for many high-precision measurements. This theory allows us to consider fluctuations from both atoms and light and leads to a detailed analysis of back-action (of light back onto the atoms) and its effect on dynamics and measurement noise in atom interferometry. From this analysis, we obtain a Standard Quantum Limit for matter-wave interferometry. We also give a comparison between the LIGO detector and matter-wave interferometer from the perspective of quantum measurement.
\r\n\r\nIn Chapter VI, we switch focus from measurement to gravitational wave sources. Specifically, we study high-frequency gravitational radiation from the ringdown of a binary black hole merger. We study the high-precision modeling on both temporal and spatial features of ringdown wave to propose a more complete test of General Relativity. We show that spin-weighted spheroidal harmonics, rather than spin-weighted spherical harmonics, better represent ringdown angular patterns. We also study the correlation between progenitor binary properties and the excitation of quasinormal modes, including higher-order angular modes, overtones, prograde and retrograde modes. This chapter seeks to provide an analytical strategy and inspire the future development of ringdown tests using data from real gravitational wave events.
", "doi": "10.7907/ks5c-zn93", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" } ]