Cosmic Polarization Rotation: an Astrophysical Test of Fundamental Physics

TL;DR

This paper reviews astrophysical tests for cosmic polarization rotation (CPR), which could indicate violations of fundamental physics principles, and summarizes current constraints and future prospects for detecting or limiting CPR.

Contribution

It provides a comprehensive review of observational tests for CPR using radio, ultraviolet, and CMB polarization data, and discusses future improvements.

Findings

Current tests have not detected CPR, with upper limits around one degree.

Results support the validity of fundamental principles like the Einstein equivalence principle.

Future observations may further tighten constraints or detect CPR.

Abstract

Possible violations of fundamental physical principles, e.g. the Einstein equivalence prin- ciple on which all metric theories of gravity are based, including general relativity (GR), would lead to a rotation of the plane of polarization for linearly polarized radiation traveling over cosmological distances, the so-called cosmic polarization rotation (CPR). We review here the astrophysical tests which have been carried out so far to check if CPR exists. These are using the radio and ultraviolet polarization of radio galaxies and the polarization of the cosmic microwave background (both E-mode and B-mode). These tests so far have been negative, leading to upper limits of the order of one degree on any CPR angle, thereby increasing our confidence in those physical principles, including GR. We also discuss future prospects in detecting CPR or improving the constraints on it.