# Frequency variation for in vacuo photon propagation in the Standard-Model Extension

## TL;DR

This paper explores how Lorentz symmetry violation in the Standard-Model Extension affects photon frequency stability in vacuum, leading to potential shifts that could impact cosmological observations.

## Contribution

It demonstrates that Lorentz symmetry violation causes frequency shifts in photons in vacuum, revealing a new aspect of energy non-conservation in the SME framework.

## Key findings

- Photon frequency is not conserved in vacuum under LSV.
- Frequency shifts can be red or blue, depending on LSV.
- Potential implications for cosmological measurements.

## Abstract

In the presence of Lorentz Symmetry Violation (LSV) associated with the Standard-Model Extension (SME), we have recently shown the non-conservation of the energy-momentum tensor of a light-wave crossing an Electro-Magnetic (EM) background field even when the latter and the LSV are constant. Incidentally, for a space-time dependent LSV, the presence of an EM field is not necessary. Herein, we infer that in a particle description, the energy non-conservation for a photon implies violation of frequency invariance in vacuo giving rise to a red or blue shift. We discuss the potential consequences on cosmology.