Gravitational radiation from compact binaries in scalar-tensor gravity

TL;DR

This paper develops second post-Newtonian gravitational waveforms for inspiraling compact binaries in scalar-tensor gravity, highlighting potential deviations from general relativity that could be detected by future gravitational-wave observations.

Contribution

It extends waveform calculations to scalar-tensor theories at 2PN order, incorporating hereditary effects and identifying parameters that distinguish these theories from GR.

Findings

Waveforms differ from GR by a small set of parameters.

Binary black hole waveforms are indistinguishable from GR.

Black hole-neutron star systems show deviations characterized by a single parameter.

Abstract

General relativity (GR) has been extensively tested in the solar system and in binary pulsars, but never in the strong-field, dynamical regime. Soon, gravitational-wave (GW) detectors like Advanced LIGO and eLISA will be able to probe this regime by measuring GWs from inspiraling and merging compact binaries. One particularly interesting alternative to GR is scalar-tensor gravity. We present progress in the calculation of second post-Newtonian (2PN) gravitational waveforms for inspiraling compact binaries in a general class of scalar-tensor theories. The waveforms are constructed using a standard GR method known as "direct integration of the relaxed Einstein equations," appropriately adapted to the scalar-tensor case. We find that differences from general relativity can be characterized by a reasonably small number of parameters. Among the differences are new hereditary terms which depend on the past history of the source. In one special case, binary black hole systems, we find that the waveform is indistinguishable from that of general relativity. In another, mixed black hole-neutron star systems, all differences from GR can be characterized by only a single parameter.