# Searches for Lorentz-Violating Signals with Astrophysical Polarization Measurements

## TL;DR

This paper reviews how astrophysical polarization measurements, especially from high-redshift objects and gamma-ray telescopes, are used to constrain Lorentz and CPT invariance violations in the photon sector within the Standard-Model Extension framework.

## Contribution

It provides a comprehensive review of methods and recent results in constraining Lorentz and CPT violation using astrophysical polarization data.

## Key findings

- Constraints on vacuum birefringence from polarization measurements.
- Limits on Lorentz violation parameters from gamma-ray observations.
- Evidence supporting Lorentz invariance at astrophysical scales.

## Abstract

Astrophysical observations are a powerful tool to constrain effects of Lorentz-invariance violation in the photon sector. Objects at high redshifts provide the longest possible baselines, and gamma-ray telescopes allow us to observe some of the highest energy photons. Observations include polarization measurements and time-of-flight measurements of transient or variable objects to constrain vacuum birefringence and dispersion. Observing multiple sources covering the entire sky allows the extraction of constraints on anisotropy. In this paper, I review methods and recent results on Lorentz- and CPT-invariance violation constraints derived from astrophysical polarization measurements in the framework of the Standard-Model Extension.