Research

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Systematic biases in ppE tests due to neglecting millilensing effects

A. Liu, R.S.Chandramouli, O. A. Hannuksela, N. Yunes, T.G.F. Li, (2024)

We analyzed systematic biases in ppE tests induced by neglecting millilensing effects. We found significant biases in -1PN, 1PN, and 2PN tests when the millilensing effects are large i.e., more alignment between the source, lens, and detector. The biases are not instances of false GR deviations due to large loss in SNR when using the unlensed ppE model. The results are currently under review in PRD (preprint version).

Systematic biases in ppE tests due to neglecting spin precession and higher modes

R.S.Chandramouli, K.Prokup, E. Berti, N.Yunes (2024)

We investigated the systematic bias induced by neglecting spin precession and higher modes. We find that for highly precessing binaries, there are significant biases in -1PN, 1PN and 2PN ppE tests of GR even at SNR of 30. Using the fitting factor of the ppE model and the Bayes factor between the ppE and GR models, we classified the statistical significance of potential GR deviations. This allow us to determine in which cases a false GR deviation can arise due to waveform mismodeling. We find that the biases due to precession are not cases of false GR deviations due to the sufficiently low fitting factor of the ppE model (loss of SNR). Also, the biases due to excluding higher modes are not significant for typical binaries observable by LVK. Lastly, we developed a toy model to illustrate analytically how the ppE biases depend on the mismodeled GW phase. Our results our published in PRD (publication version, preprint version).

First constraints on dissipative tidal effects

J.Ripley, A.Hegade, R.S.Chandramouli, N. Yunes (2023)

We analyzed data from the binary neutron star event GW170817 and obtained the first constraint on the dissipative tidal deformability which is potentially induced by internal dissipative (viscous) processes. Our constraint makes contact with nuclear physics by indirectly probing finite temperature and out-of-equilibrium effects. By assuming an average temperature, we placed preliminary constraints on the viscosity profile of the neutron star. More detailed analysis is needed to directly measure the temperature of the stars and to infer specific microphysics models. We also forecasted of the potential detectability (an improvement over just a constraint) of the dissipative tidal deformability with future gravitational wave observations. The results are published in Nature Astronomy (journal version, preprint version).

Ready-to-use analytic waveforms with leading order Kozai-Lidov oscillations

R.S.Chandramouli, N.Yunes (2022)

We constructed `read-to-use' Fourier-domain gravitational waveforms from an inner binary in a hierarchical triple, by accounting for the Kozai-Lidov oscillations induced by the third body. We modeled the effect to leading order in conservative and dissipative dynamics and found that there is a strong imprint on the gravitational-wave amplitude and a measurable effect on the gravitational-wave phase. Click here to view the PRD publication.