Various facets of phases in gravitational wave physics
File(s)
Author(s)
Margalit, Aoibheann
Type
Thesis
Abstract
This thesis contains two main results related to low-frequency gravitational waves. The first is a prescription for causality within low energy effective field theories (EFTs), specialised to gravitational theories. An EFT is a framework for parametrising macroscopic physics while remaining agnostic about the microscopic degrees of freedom. It turns out that the most generic naïvely local and covariant EFT action is not necessarily consistent with a physical UV theory, and thus imposing the causal propagation of waves can place non-trivial constraints on the EFT. Our criteria for “infrared causality” is that scattered waves do not experience a resolvable time advance relative to the geometry of the background. We apply this condition to the Gauss–Bonnet operator on black hole and pp-wave spacetimes and show that, within the EFT’s regime of validity, causality is respected.
The second result relates to gravitational wave backgrounds (GWBs) within the standard cosmological model. We show that scalar perturbations to the background metric ruin any phase coherence in the GWB which may have been present at emission. The main consequence is that phase-coherent mapping methods have no foreseeable application to GWBs.
The second result relates to gravitational wave backgrounds (GWBs) within the standard cosmological model. We show that scalar perturbations to the background metric ruin any phase coherence in the GWB which may have been present at emission. The main consequence is that phase-coherent mapping methods have no foreseeable application to GWBs.
Version
Open Access
Date Issued
2023-07
Date Awarded
2023-10
Copyright Statement
Creative Commons Attribution NonCommercial ShareAlike Licence
Advisor
Contaldi, Carlo
de Rham, Claudia
Sponsor
Imperial College London
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)