Date of Award
1-1-2025
Document Type
Dissertation
Degree Name
Ph.D. in Physics
First Advisor
Anuradha Gupta
Second Advisor
Luca Bombelli
Third Advisor
Jake Bennett
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Gravitational wave (GW) observations from binary black hole (BBH) coalescences offer a powerful means of probing general relativity (GR) in its most extreme regime: the strong- field, highly dynamical merger phase. One can compare observed signals to theoretical waveform models to constrain possible deviations from GR. However, the reliability of such comparisons can be compromised by waveform systematics, especially when key physical effects are not incorporated into the models. This dissertation investigates the impact of three such missing physical effects: orbital eccentricity, strong gravitational lensing, and waveform systematics due to precession, higher-order modes, and memory on standard GW tests of GR performed by the LIGO-Virgo-KAGRA (LVK) collaboration. Specifically, we consider two parameterized tests (TIGER and FTI), the modified dispersion relation (MDR) test, and the inspiral-merger-ringdown (IMR) consistency test. First, we examine how moderate orbital eccentricity, which may be present in binaries formed dynamically in dense stellar environments, can produce spurious deviations from GR when analyzed with waveform models that assume quasicircular orbits. Using non-spinning numerical relativity (NR) waveforms with eccentricities of ̴ 0:05-0:1 at 17 Hz and mass ratios of 1, 2, 3, we demonstrate that TIGER, FTI, MDR, and IMR consistency tests can falsely signal GR violations even at moderate signal-to-noise ratios. Next, we explore the influence of strong gravitational lensing, particularly Type II images, which introduce a characteristic π/2 phase shift to the waveform. For binaries with total masses of 20Mꙩ and 80Mꙩ, high spins (χ = 0:5 and 0:95), and significant precession, we show that Type II lensing can mimic GR deviations in the TIGER and MDR tests, especially for higher mass ratios and stronger precession. Finally, we study the biases introduced by semi-analytic waveform models that neglect higher-order modes, precession, and memory by injecting NR waveforms and recovering them using state-of-the-art precessing waveform models that neglect some sub-dominant harmonic modes. We find that the omission of higher modes can lead to notable discrepancies in the recovered post-inspiral testing parameters in TIGER, highlighting the importance of model completeness in reliable GR inference. Together, these studies underscore the necessity of incorporating all relevant physical effects within waveform models to avoid false indications of GR violations. As detector sensitivity improves and GW catalogs expand, addressing these sources of systematic error will be essential for robust and meaningful tests of gravity theories.
Recommended Citation
Narayan, Purnima, "Missing Physics or New Physics? Understanding Biases in Gravitational Wave Tests of General Relativity" (2025). Electronic Theses and Dissertations. 3339.
https://egrove.olemiss.edu/etd/3339