Gravitational Waves and Inspiraling Compact Binaries in Alternative Theories of Gravity

TL;DR

This paper investigates gravitational waves and inspiraling compact binaries within alternative gravity theories, deriving equations of motion, analyzing gravitational radiation, and exploring Lorentz invariance violations to compare with general relativity predictions.

Contribution

It provides explicit post-Newtonian calculations for compact binaries in scalar-tensor theories and develops a parametrized framework for Lorentz violation effects on gravitational wave propagation.

Findings

Binary black hole motion matches general relativity at 2.5PN order

Dipole gravitational radiation influences binary dynamics at 1.5PN order

Constraints on Lorentz violation can be derived from gravitational wave observations

Abstract

This dissertation consists of four parts. In Part I, we briefly review fundamental theories of gravity, performed experimental tests, and gravitational waves. The framework and the methods that we use in our calculations are discussed in Part II. This part includes reviewing the methods of the Parametrized Post-Newtonian (PPN) framework, Direct Integration of Relaxed Einstein Equations (DIRE), and Matched Filtering. In Part III, we calculate the explicit equations of motion for non-spinning compact objects (neutron stars or black holes) to 2.5 post-Newtonian order, or $O(v/c)^5$ beyond Newtonian gravity, in a general class of alternative theories to general relativity known as scalar-tensor theories. For the conservative part of the motion, we obtain the two-body Lagrangian and conserved energy and momentum through second post-Newtonian order. We find the contributions to gravitational radiation reaction to 1.5 post-Newtonian and 2.5 post-Newtonian orders, the former corresponding to the effects of dipole gravitational radiation. For binary black holes we show that the motion through 2.5 post-Newtonian order is observationally identical to that predicted by general relativity. In Part IV, we construct a parametrized dispersion relation that can produce a range of predictions of alternative theories of gravity for violations of Lorentz invariance in gravitation, and investigate their impact on the propagation of gravitational waves. We show how such corrections map to the waveform observable by a gravitational-wave detector, and to the "parametrized post-Einsteinian framework", proposed to model a range of deviations from General Relativity. Given a gravitational-wave detection, the lack of evidence for such corrections could then be used to place a constraint on Lorentz violation.