Gravitational wave birefringence in spatially curved teleparallel cosmology

TL;DR

This paper investigates how certain teleparallel gravity theories predict gravitational wave birefringence and dispersion effects that depend on the universe's spatial curvature and deviations from General Relativity.

Contribution

It demonstrates that in a class of teleparallel gravity theories, gravitational waves exhibit birefringence and dispersion depending on background curvature and theory parameters.

Findings

Gravitational wave birefringence depends on spatial curvature.

Dispersion relations vary with polarization and wave number.

Effect magnitude relates to deviation from General Relativity.

Abstract

We study tensor perturbations around the most general cosmologically symmetric backgrounds in a class of teleparallel gravity theories known as New General Relativity. These theories comprise a one-parameter class, which is fully consistent with observations at the post-Newtonian level, and which contains the teleparallel equivalent of General Relativity as a special case. We find that for a particular class of cosmological background geometries these theories exhibit gravitational wave birefringence and dispersion, i.e., the dispersion relation for gravitational waves depends on their polarization and wave number. The strength of this effect is directly related to the spatial curvature of the cosmological background and the parameter describing the deviation of the theory from General Relativity. We discuss the possibility of observing this effect in gravitational wave experiments.