Comparing solar-system, binary-pulsar, and gravitational-wave tests of gravity

TL;DR

This paper compares the effectiveness of solar-system, binary-pulsar, and gravitational-wave tests in probing gravity, highlighting the unique constraints strong-field tests provide on alternative theories like tensor-scalar models.

Contribution

It demonstrates that strong-field tests uniquely constrain theories indistinguishable from general relativity in the solar system, and binary-pulsar data already exclude certain scalar effects.

Findings

Strong-field tests differ qualitatively from weak-field experiments.

Binary-pulsar data rule out scalar effects detectable by LIGO/VIRGO.

General relativity suffices for 'chirp' template computations.

Abstract

This talk is based on my work in collaboration with Thibault Damour. We compare the probing power of different classes of gravity experiments: solar-system tests (weak-field regime), binary-pulsar tests (strong-field regime), and future gravitational-wave observations of inspiralling binaries (strong-field effects detected in our weak-gravitational-field conditions). This is done within the most natural class of alternative theories to general relativity, namely tensor-scalar theories, in which the gravitational interaction is mediated by one tensor field (g_munu) together with one or several scalar fields (phi). Our main conclusion is that strong-field tests are qualitatively different from weak-field experiments: They constrain theories which are strictly indistinguishable from general relativity in the solar system. We also show that binary-pulsar data are so precise that they already rule out the theories for which scalar effects could have been detected with LIGO or VIRGO. This proves that it is therefore sufficient to compute the `chirp' templates within general relativity.