Gravitationalwave lensing in Einsteinaether theory
Abstract
Einsteinaether theory provides a model to test the validity of local Lorentz invariance in gravitational interactions. The speed of gravitational waves as measured from the binary neutron star event GW170817 sets stringent limits on Einsteinaether theory, but only on a combination of the theory's free parameters. For this reason, a significant part of the theory's parameter space remains unconstrained by observations. Motivated by this, we explore the propagation of gravitational waves in Einsteinaether theory over an inhomogeneous background (i.e., gravitational wave lensing) as a potential mechanism to break the degeneracies between the theory's free parameters, and hence enable new constraints on the theory to be obtained. By bringing the field equations into the form of the socalled kinetic matrix and applying a formalism known as the propagation eigenstate framework, we find that the speed of gravitational waves is modified by inhomogeneities in the aether field. However, the modification is common to both gravitational polarizations and vanishes in the limit in which gravitational waves propagate with luminal speed. This lensdependent gravitational wave speed contrasts with the lensinduced birefringence observed in other theories beyond general relativity, like Horndeski's theory. While the potential to improve tests based on gravitationalwave speed is limited, our formalism sets the basis to fully describe signal propagation over inhomogeneous spacetimes in Einsteinaether theory and other extensions of general relativity.
 Publication:

arXiv eprints
 Pub Date:
 April 2024
 DOI:
 10.48550/arXiv.2404.07782
 arXiv:
 arXiv:2404.07782
 Bibcode:
 2024arXiv240407782S
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 19 pages plus appendices, 4 figures