Title: Uncovering Missing Physics: Eccentricity and Strong Gravitational Lensing Effects on GW Tests of GR
Abstract: The detection of gravitational waves (GWs) from binary black hole (BBH) coalescences offers a powerful tool for exploring the strong-field regime of general relativity (GR). To ensure the reliability of these tests, it is essential to identify and address potential sources of error, particularly those arising from missing physics in the waveform models used in GW data analysis. Specifically, effects such as eccentricity and strong gravitational lensing are not currently accounted for in GW tests of GR. In this study, we apply four tests of GR to simulated signals with eccentricity and to quasicircular signals subjected to Type II strong gravitational lensing, in the LIGO-Virgo network. Our results reveal that signals with eccentricities ~ 0.1 upon entering the detector's sensitive band can produce spurious GR deviations. Furthermore, Type II lensing of signals with highly unequal masses and precession can lead to substantial false GR deviations in certain tests. These findings underscore the importance of excluding the possibility of missing physics, such as an eccentric or strongly lensed GW signal, before asserting the detection of a GR deviation.