Testing the strong equivalence principle with gravitational-wave observations of binary black holes

TL;DR

This paper discusses how gravitational-wave observations from binary black holes can test the strong equivalence principle, exploring potential deviations from General Relativity in the strong-field regime.

Contribution

It reviews the formalism for extra gravitational emission channels and highlights how binary black-hole data can test theories distinct from those tested by pulsars.

Findings

Binary black-hole observations can probe new gravitational theories.

Current LIGO data is consistent with General Relativity.

Future observations will improve tests of the strong equivalence principle.

Abstract

The recent LIGO detection of gravitational waves from black-hole binaries offers the exciting possibility of testing gravitational theories in the previously inaccessible strong-field, highly relativistic regime. While the LIGO detections are so far consistent with the predictions of General Relativity, future gravitational-wave observations will allow us to explore this regime to unprecedented accuracy. One of the generic predictions of theories of gravity that extend General Relativity is the violation of the strong equivalence principle, i.e. strongly gravitating bodies such as neutron stars and black holes follow trajectories that depend on their nature and composition. This has deep consequences for gravitational-wave emission, which takes place with additional degrees of freedom besides the tensor polarizations of General Relativity. I will briefly review the formalism needed to describe these extra emission channels, and show that binary black-hole observations probe a set of gravitational theories that are largely disjoint from those that are testable with binary pulsars or neutron stars.