Testing gravity with the two-body problem

TL;DR

This paper develops a new theoretical framework using Effective Field Theory to compare predictions of General Relativity and scalar-tensor theories for gravitational waves from two-body systems, aiding tests of gravity.

Contribution

It introduces a novel Non-Relativistic Scalar-Tensor formalism and an EFT approach for gravitational wave generation in scalar-hair theories, advancing the analysis of alternative gravity models.

Findings

Embedded scalar-tensor theories in NRGR framework

Studied disformal scalar coupling effects on two-body dynamics

Developed EFT formalism for gravitational wave generation with scalar hair

Abstract

Gravitational waves provide a new probe into the strong-field regime of gravity. It is thus essential to identify the predictions of General Relativity on the nature of the two-body problem, and to contrast them to alternative theories. This thesis aims at comparing the predictions of General Relativity and scalar-tensor theories on gravitational observables using Effective Field Theory techniques. In a first part, we show how simple scalar-tensor theories can be embedded in the Non-Relativistic General Relativity approach to the two-body problem and highlight their essential features. Furthermore, we study the effects of a disformal coupling of the scalar on the two-body dynamics and introduce a resummation technique. This new Non-Relativistic Scalar-Tensor formalism will provide a basis for the study of the Vainshtein mechanism in two-body configurations which is at the core of the second part of this thesis. Finally, in a last part we devise an Effective Field Theory formalism adapted to gravitational wave generation in theories featuring scalar hair, in the extreme mass ratio regime.