Tidal effects in gravitational waves from neutron stars in scalar-tensor theories of gravity

TL;DR

This paper analyzes how scalar-tensor theories of gravity affect tidal signatures in gravitational waves from neutron star binaries, revealing that these effects are generally smaller than in General Relativity due to different frequency scalings.

Contribution

It provides the first detailed calculation of tidal Love numbers and their impact on GW signals in scalar-tensor gravity, including mode analysis and parameter dependencies.

Findings

Tidal effects in scalar-tensor theories are smaller than in GR.

Different tidal contributions can have opposite signs and scalings.

Net tidal imprints are reduced compared to GR for the same systems.

Abstract

We compute tidal signatures in the gravitational waves (GWs) from neutron star binary inspirals in scalar-tensor gravity, where the dominant adiabatic even-parity tidal interactions involve three types of Love numbers that depend on the matter equation of state and parameters of the gravitational theory. We calculate the modes of the GW amplitudes and the phase evolution in the time and frequency domain, working up to first order in the post-Newtonian and small finite-size approximations. We also perform several case studies to quantify the dipolar and quadrupolar tidal effects and their parameter dependencies specialized to Gaussian couplings. We show that various tidal contributions enter with different signs and scalings with frequency, which generally leads to smaller net tidal GW imprints than for the same binary system in General Relativity.