Constraint on Brans-Dicke theory from intermediate/extreme mass ratio inspirals

TL;DR

This paper uses gravitational wave observations of intermediate and extreme mass ratio inspirals to place the tightest constraints on Brans-Dicke theory, highlighting the importance of monopolar and dipolar emissions in waveform modeling.

Contribution

It develops accurate waveform templates including monopolar and dipolar effects in Brans-Dicke theory for I/EMRIs, enabling stringent tests of gravity.

Findings

Most stringent constraint on Brans-Dicke parameter: ω₀ > 10^6

Two-year LISA observation can effectively test alternative gravity theories

Inclusion of monopolar and dipolar emissions significantly impacts waveform accuracy

Abstract

Intermediate/Extreme mass ratio inspiral (I/EMRI) system provides a good tool to test the nature of gravity in strong field. Based on the method of osculating orbits, we compute the orbital evolutions of I/EMRIs on quasi-elliptic orbits in both Einstein's general relativity and Brans-Dicke theory. The extra monopolar and dipolar channels in Brans-Dicke theory accelerate the orbital decay, so it is important to consider the effects of monopolar and dipolar emissions on the waveform. With the help of accurate orbital motion, we generate waveform templates which include both monopolar and dipolar contributions for I/EMRIs on eccentric orbits in Brans-Dicke theory. With a two-year observation of gravitational waves emitted from I/EMRIs by LISA, we get the most stringent constraint on the Brans-Dicke coupling parameter $\omega_0>10^6$.