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Public viva-voce Notification Date: Wednesday, 11 September 2024 Time: 3:30 - 6:00 PM Venue: Seminar Hall Astrophysics and tests of general relativity with gravitational waves from compact binaries in elliptical orbits Pankaj Saini Chennai Mathematical Institute. 11-09-24 Abstract Orbital eccentricity of compact binaries (black holes and neutron stars), when observed by gravitational wave (GW) detectors such as LIGO/Virgo, is believed to be a powerful discriminant of the formation channels of these binaries. Binaries formed via isolated binary evolution in the galactic fields would get enough time to circularize by the time they merge due to GW radiation reaction. On the other hand, a subpopulation of binaries formed by dynamical interactions in dense clusters may retain a residual eccentricity even close to the merger. Therefore, different formation channels are expected to follow different eccentricity distributions. Orbital eccentricity of compact binaries (black holes and neutron stars), when observed by gravitational wave (GW) detectors such as LIGO/Virgo, is believed to be a powerful discriminant of the formation channels of these binaries. Binaries formed via isolated binary evolution in the galactic fields would get enough time to circularize by the time they merge due to GW radiation reaction. On the other hand, a subpopulation of binaries formed by dynamical interactions in dense clusters may retain a residual eccentricity even close to the merger. Therefore, different formation channels are expected to follow different eccentricity distributions. Gravitational wave observations provide a unique opportunity to test general relativity (GR) in the strong-field and highly dynamical regime of the theory. Tests of GR currently employ quasicircular waveforms since binaries are expected to be circularized when entering the frequency band of ground-based detectors due to the emission of GWs. Neglecting eccentricity in the waveform model can lead to systematic biases in tests of GR that could mimic GR violations. We investigate the impact of residual binary eccentricity on tests of GR. In particular, we study the systematic biases on the parametrized test and inspiral-merger-ringdown (IMR) consistency test, when a phasing based on the circular orbit assumption is employed for a system that has some small residual eccentricity. Given the sensitivity of current detectors, the systematic bias may be hidden by the large statistical uncertainty due to detector noise. For loud events, even a small shift in the “true” value of the testing GR parameter may significantly bias the test of GR. We find that for parametrized tests, systematic errors in testing GR parameters exceed the statistical errors even for eccentricities as small as 0.04 for Advanced LIGO. In the case of CE, systematic biases become dominant even for smaller eccentricities 0.005. For the IMR consistency test, we investigated the effect of neglecting orbital eccentricity on the final mass and final spin estimated from the inspiral portion of the signal. We find that the systematic errors in the remnant final mass and final spin become statistically significant in the CE band at eccentricity ~ 0.015. In the LIGO band, systematic errors become statistically significant only at relatively higher eccentricities
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