Lorentz violation induced vacuum birefringence and its astrophysical consequences

TL;DR

This paper explores how Lorentz violation in loop quantum gravity causes vacuum birefringence, leading to observable effects like peak doubling and de-polarization in astrophysical light, and derives new constraints from gamma-ray polarization data.

Contribution

It introduces the phenomena of peak doubling and de-polarization due to Lorentz violation and provides the most stringent constraint on the Lorentz-violating parameter from astrophysical observations.

Findings

Upper limit of ~8.7×10⁻¹² on Lorentz-violating parameter χ

Predicted observable effects include peak doubling and de-polarization

Suggested analysis of Fermi LAT GRBs for peak doubling evidence

Abstract

In the electromagnetism of loop quantum gravity, two helicities of a photon have different phase velocities and group velocities, termed as "vacuum birefringence". Two novel phenomenons, "peak doubling" and "de-polarization", are expected to appear for a linearly polarized light from astrophysical sources. We show that the criteria to observe these two phenomenons are the same. Further, from recently observed $\gamma$-ray polarization from Cygnus X-1, we obtain an upper limit $\sim 8.7\times10^{-12}$ for Lorentz-violating parameter $\chi$, which is the most firm constraint from well-known systems. We also suggest to analyze possible existence of "peak doubling" through Fermi LAT GRBs.