Gravitational waves in scalar-tensor theory to one-and-a-half post-Newtonian order

TL;DR

This paper calculates gravitational wave signals from compact binaries in scalar-tensor theories up to 1.5 post-Newtonian order, including new scalar modes and tail effects, aiding gravitational wave data analysis.

Contribution

It extends the post-Newtonian formalism to scalar-tensor theories at 1.5PN order, incorporating scalar modes, tail, and memory effects for the first time.

Findings

Derived multipole moments and GW flux including 1.5PN corrections.

Presented templates for data analysis of gravitational wave detectors.

Provided scalar gravitational wave modes for comparison with numerical relativity.

Abstract

We compute the gravitational waves generated by compact binary systems in a class of massless scalar-tensor (ST) theories to the 1.5 post-Newtonian (1.5PN) order beyond the standard quadrupole radiation in general relativity (GR). Using and adapting to ST theories the multipolar-post-Minkowskian and post-Newtonian formalisms originally defined in GR, we obtain the tail and non-linear memory terms associated with the dipole radiation in ST theory. The multipole moments and GW flux of compact binaries are derived for general orbits including the new 1.5PN contribution, and comparison is made with previous results in the literature. In the case of quasi-circular orbits, we present ready-to-use templates for the data analysis of detectors, and for the first time the scalar GW modes for comparisons with numerical relativity results.