Effective Field Theory for Gravitational Radiation in General Relativity and beyond

TL;DR

This thesis develops an effective field theory approach to gravitational radiation in general relativity and scalar-tensor theories, simplifying calculations and extending methods to include scalar fields and alternative gravity models.

Contribution

It introduces the Kaluza-Klein parametrization for higher-order post-Newtonian calculations and extends it to conformally-coupled scalar-tensor gravity, providing new tools for binary system analysis.

Findings

Validated the effective field theory approach for binary black holes in GR

Extended the Kaluza-Klein parametrization to scalar-tensor gravity

Derived the gravitational action with a conformally coupled scalar field

Abstract

The topic of this thesis is the so-called Non-Relativistic General Relativity, an effective field theory approach proposed by Goldberger and Rothstein to study the conservative and dissipative dynamics of binary systems of compact objects in the post-Newtonian expansion. In the first part of the thesis we review this approach in the simplest possible case: a binary of non-spinning black holes at leading post-Newtonian order, both for the conservative and dissipative sector in general relativity. In the second part of the thesis we present the so-called Kaluza-Klein parametrization of the metric. Introduced by Kol and Smolkin, it allows to simplify the computations in the conservative sector at higher order in the post-Newtonian expansion. We then extend this parametrization to (conformally-coupled) scalar-tensor gravity. In particular, we derive in details the gravitational action in a generic metric frame, including for the first time a conformally coupled scalar field. Using this formalism, we study the conservative and dissipative dynamics of a binary system of bodies conformally coupled to the metric, at leading post-Newtonian order, and compare this with the standard general relativity results. This thesis is aimed at a reader that approaches the field for the first time. Hence, we attempted to be as pedagogical, explicit and self-contained as possible.