On the Photon Mass

TL;DR

This paper reviews the possibility of a tiny photon mass, discusses experimental tests including Lorentz symmetry violations, and suggests existing high-energy astrophysical observations might already indicate such effects.

Contribution

It provides a comprehensive review of experimental tests for photon mass and explores potential evidence from high-energy cosmic phenomena.

Findings

Photon mass could be compatible with current experimental limits

High-energy gamma ray and cosmic ray tests may indicate Lorentz violations

Existing astrophysical data might already suggest a non-zero photon mass

Abstract

We review the case for the photon having a tiny mass compatible with the experimental limits. We go over some possible experimental tests for such a photon mass including the violation of Lorentz symmetry. We point out that such violations may already have been witnessed in tests involving high energy gamma rays from outer space as also ultra high energy cosmic rays.