Gravitational waves from eccentric extreme mass-ratio inspirals as probes of scalar fields

Abstract

We study eccentric orbits of the Schwarzschild spacetime for extreme mass ratio system (EMRI) in modified gravity theories with additional scalar fields. Due to the additional energy and angular momentum carried away by the scalar field, the orbit of the EMRI in modified gravity decays faster than that in general relativity. The time that it takes the eccentricity e to reach the minimum is shorter and the values of the semi-latus rectum p and e at the turning point when e reaches the minimum are bigger for larger scalar charge d. In addition to the calculation of energy fluxes with numerical methods, we also use the Post-Newtonian expansion of the rate of energy carried away by the scalar field in eccentric orbits to understand the behaviors of the energy emission. By adding the scalar flux to the open code FastEMRIWaveforms of the Black Hole Perturbation Toolkit, we numerically generate fast gravitational waveforms for eccentric EMRIs with scalar fields and use the faithfulness between waveforms with and without the scalar charge to discuss the detection of scalar charge d. The detection error of the scalar charge is also estimated with the method of the Fisher information matrix.

Test of the Brans–Dicke theory with GW200105 and GW200115

“…The larger initial eccentricity helps constrain the BD parameter ω BD . As we can see, the eccentricity can excite additional energy flux channels from monopole mode and quadrupolar mode for the scalar field [78]. So the dephasing caused by the scalar field for the eccentric orbit will be larger than the circular orbit, thus constraining the BD parameter ω BD better.…”