Gravity-induced birefringence within the framework of Poincare gauge theory

TL;DR

This paper demonstrates that Poincaré gauge theory predicts gravity-induced birefringence affecting light polarization, provides an explicit phase shift expression, and uses white dwarf data to constrain the coupling constant.

Contribution

It introduces the first explicit formula for polarization phase shift in Poincaré gauge theory and links it to observable astrophysical data.

Findings

Gravity-induced birefringence predicted by Poincaré gauge theory.

Explicit expression for polarization phase shift derived.

Constraints on coupling constant from white dwarf polarimetry.

Abstract

Gauge theories of gravity provide an elegant and promising extension of general relativity. In this paper we show that the Poincar\'e gauge theory exhibits gravity-induced birefringence under the assumption of a specific gauge invariant nonminimal coupling between torsion and Maxwell's field. Furthermore we give for the first time an explicit expression for the induced phaseshift between two orthogonal polarization modes within the Poincar\'e framework. Since such a phaseshift can lead to a depolarization of light emitted from an extended source this effect is, in principle, observable. We use white dwarf polarimetric data to constrain the essential coupling constant responsible for this effect.