Bounds on Parity Violation In the Cosmological Redshift

TL;DR

This paper investigates potential parity violation in the cosmological redshift by analyzing how differential redshift for polarized photons could cause depolarization, providing constraints based on gamma-ray burst observations.

Contribution

It introduces a novel approach to test parity violation in gravity through cosmological redshift effects on polarized light, deriving bounds from observational data.

Findings

Right- and left-circular polarization redshift difference constrained to 6 x 10^(-37)

Depolarization signature depends on redshift squared, z^2

No evidence of parity violation observed in gamma-ray burst polarization

Abstract

Parity (P) violation in gravity would be a sure sign of new physics. We examine the possibility of P violation in the cosmological redshift. If right- and left-circularly polarized photons experience the redshift differently, the radiation from distant sources would tend to be depolarized, since the polarizations states would accumulate different phases during propagation. The resulting birefringence has an unusual signature--depending on z^2--quite unlike what is seen in other theories, including those with violation of local boost invariance. The observed broad-spectrum polarization of $\gamma$-ray bursts constrains the fractional difference between the right- and left-handed redshifts at the 6 x 10^(-37) level.