{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/129843"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/129843","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Fundamental physics in extreme-gravity environments","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-10-20 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-10-20 without embargo terms","abstract_has_math":false,"creators":["Xie, Yiqi"],"institution":"University of Illinois Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Yunes, Nicolás","Gammie, Charles F.","Holder, Gilbert","Narayan, Gautham"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-07-16","date_published":"2025-07-16","updated_at":"2026-07-22T22:25:05Z","subjects":["Compact Objects","Gravitational Waves","Tests Of General Relativity","Fundamental Physics","Phenomenology","Data Analysis"],"languages":["en","eng"],"rights":["Copyright 2025 Yiqi Xie"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/129843","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Yunes, Nicolás","Gammie, Charles F.","Holder, Gilbert","Narayan, Gautham"]},{"key":"dc:creator","label":"Author","values":["Xie, Yiqi"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2025-07-16","2025-08"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Compact Objects","Gravitational Waves","Tests Of General Relativity","Fundamental Physics","Phenomenology","Data Analysis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2025 Yiqi Xie"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/129843"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-10-20 without embargo terms","The student, Yiqi Xie, accepted the attached license on 2025-07-07 at 13:20.","The student, Yiqi Xie, submitted this Dissertation for approval on 2025-07-11 at 15:50.","This Dissertation was approved for publication on 2025-07-16 at 08:52.","DSpace SAF Submission Ingestion Package generated from Vireo submission #22430 on 2025-10-20 at 16:57:30","Extreme gravity sourced by compact objects and their coalescences is a great avenue for testing Einstein’s general relativity and is deeply interconnected with fundamental physics. In this dissertation, we discuss three topics on the interplay between extreme gravity and fundamental physics driven by recent observational advancements. The first topic concerns making predictions about black holes in modified gravity. We prove that the spacetimes of isolated black holes in a broad class of modified gravity theories must be circular, justifying the long-existing use of a circular ansatz to simplify black hole solutions in these theories. We then analytically calculate the observables of the Blandford–Znajek process around a supermassive black hole in quadratic gravity. The calculation reveals a degeneracy between the black hole’s spin and the quadratic coupling, which hinders such an effect from constraining quadratic gravity unless the black hole is fast-spinning. The second topic concerns deciphering fundamental physics implications in gravitational-wave data from observations of compact binary coalescences. We search over the current gravitational-wave transient catalog for activated dipolar emission from massive scalar fields nonminimally coupled to gravity. Our Bayesian analysis suggests no evidence for these fields and places the most stringent upper-bound constraints on their coupling strengths. We then generalize the above search and combine it with the LIGO-Virgo-KAGRA parametrized inspiral tests of general relativity. This is achieved by extending the parametrized post-Einsteinian framework behind these tests using neural networks. We find that the resulting new framework leads to more theory-agnostic and more efficient tests of general relativity using gravitational waves. The third topic concerns improving gravitational-wave measurements of compact binary coalescences using domain knowledge from nuclear astrophysics. We show that modeling binary neutron star signals with binary Love relations breaks the distance-inclination degeneracy and improves the measurement of the neutron star masses. We forecast the decrease in the measurement error in the era of third-generation detectors, and we relax the assumptions behind our approach to prove the robustness of our forecasts."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Fundamental physics in extreme-gravity environments"]}]}],"canonical_facts":{"dc:contributor":["Yunes, Nicolás","Gammie, Charles F.","Holder, Gilbert","Narayan, Gautham"],"dc:creator":["Xie, Yiqi"],"dc:date":["2025-07-16","2025-08"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-10-20 without embargo terms","The student, Yiqi Xie, accepted the attached license on 2025-07-07 at 13:20.","The student, Yiqi Xie, submitted this Dissertation for approval on 2025-07-11 at 15:50.","This Dissertation was approved for publication on 2025-07-16 at 08:52.","DSpace SAF Submission Ingestion Package generated from Vireo submission #22430 on 2025-10-20 at 16:57:30","Extreme gravity sourced by compact objects and their coalescences is a great avenue for testing Einstein’s general relativity and is deeply interconnected with fundamental physics. In this dissertation, we discuss three topics on the interplay between extreme gravity and fundamental physics driven by recent observational advancements. The first topic concerns making predictions about black holes in modified gravity. We prove that the spacetimes of isolated black holes in a broad class of modified gravity theories must be circular, justifying the long-existing use of a circular ansatz to simplify black hole solutions in these theories. We then analytically calculate the observables of the Blandford–Znajek process around a supermassive black hole in quadratic gravity. The calculation reveals a degeneracy between the black hole’s spin and the quadratic coupling, which hinders such an effect from constraining quadratic gravity unless the black hole is fast-spinning. The second topic concerns deciphering fundamental physics implications in gravitational-wave data from observations of compact binary coalescences. We search over the current gravitational-wave transient catalog for activated dipolar emission from massive scalar fields nonminimally coupled to gravity. Our Bayesian analysis suggests no evidence for these fields and places the most stringent upper-bound constraints on their coupling strengths. We then generalize the above search and combine it with the LIGO-Virgo-KAGRA parametrized inspiral tests of general relativity. This is achieved by extending the parametrized post-Einsteinian framework behind these tests using neural networks. We find that the resulting new framework leads to more theory-agnostic and more efficient tests of general relativity using gravitational waves. The third topic concerns improving gravitational-wave measurements of compact binary coalescences using domain knowledge from nuclear astrophysics. We show that modeling binary neutron star signals with binary Love relations breaks the distance-inclination degeneracy and improves the measurement of the neutron star masses. We forecast the decrease in the measurement error in the era of third-generation detectors, and we relax the assumptions behind our approach to prove the robustness of our forecasts."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/129843"],"dc:language":["en","eng"],"dc:rights":["Copyright 2025 Yiqi Xie"],"dc:subject":["Compact Objects","Gravitational Waves","Tests Of General Relativity","Fundamental Physics","Phenomenology","Data Analysis"],"dc:title":["Fundamental physics in extreme-gravity environments"],"dc:type":["text"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:05Z"}