Etherington's Distance Duality with Birefringence

TL;DR

This paper explores how weak birefringence in spacetime, derived from gravitational closure, modifies the Etherington distance duality relation, highlighting observable effects of non-metricities in birefringent electrodynamics.

Contribution

It provides the first concrete example of how non-metricities from gravitational closure of birefringent electrodynamics affect distance relations.

Findings

Modified Etherington relation in weak gravitational fields

Demonstrates observable effects of non-metricities

First concrete example linking birefringence to distance duality

Abstract

We consider light propagation in a spacetime whose kinematics allow weak birefringence, and whose dynamics have recently been derived by gravitational closure. Revisiting the definitions of luminosity and angular diameter distances in this setting, we present a modification of the Etherington distance duality relation in a weak gravitational field around a point mass. This provides the first concrete example of how the non-metricities implied by gravitational closure of birefringent electrodynamics affect observationally testable relations.