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Waveform modelling for gravitational wave astrophysics

Kolitsidou, Panagiota 2023. Waveform modelling for gravitational wave astrophysics. PhD Thesis, Cardiff University.
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The advancing sensitivity of gravitational wave detectors not only broadens our knowledge of the universe but also calls for the refinement of the waveform models. The focus of this thesis is the study of the impact that the absence of the multipole asymmetry from the waveform models has on the measured binary black hole parameters and the development of more accurate Phenom waveform models by modelling this missing physics. We conduct a systematics study to investigate the impact of the absence of this asymmetry using two versions of NRSur7dq4, the original NRSur7dq4 and a “symmetric” NRSur7dq4, where the asymmetry is removed. Moreover, we show how the introduced biases are affected by the recoil velocity and other parameters. We also consider the highly precessing GW200129 signal. This study shows that the absence of the multipole asymmetry from the waveform models leads to significant biases in the spin measurements in the case of strongly precessing systems with high signal-to-noise ratio (SNR). Based on these results, the inclusion of the multipole asymmetry in the waveform models will be essential for the correct measurement of these parameters in the next observational runs when we expect to observe similar to these events. Therefore, we developed the first phenomenological multipole asymmetry model. Our model is implemented into PhenomPNR and will be available in O4. The amplitude and the phase of the asymmetry are modelled in the frequency-domain co-precessing frame. To model the amplitude, we use post-Newtonian (PN) expressions to compute a ratio of the anti-symmetric amplitude over the symmetric amplitude. This PN ratio is our starting point for the modelling of the corresponding numerical relativity ratio. The asymmetry amplitude model is obtained by multiplying this ratio model with one of the existing symmetrized waveform models. To model the phase, we construct the asymmetry phase derivative using the phase derivative of the symmetric phase and the derivative of the precession angle, alpha. During the inspiral, the asymmetry phase derivative is equivalent to the sum of these terms while closer to the merger it becomes equal to the derivative of the symmetric phase.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: gravitational waves, black hole, binary black holes, multipole asymmetry, precession, spin, systematics, waveform model
Funders: STFC
Date of First Compliant Deposit: 26 February 2024
Last Modified: 26 Feb 2024 12:19

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