Revealing Cosmic Rotation

TL;DR

This paper discusses how polarization measurements of the cosmic microwave background can reveal fundamental physics violations, highlighting the effectiveness of EB correlation estimators and optimizing experiments to detect cosmological birefringence amidst systematics.

Contribution

It demonstrates that EB correlation-based estimators are optimal for detecting cosmological birefringence and explores how to optimize CMB experiments considering instrumental systematics.

Findings

EB estimators have the lowest noise and are least affected by systematics.

Current polarimeters are optimized for B-mode detection, not birefringence.

Optimization strategies for CMB experiments to detect CB are proposed.

Abstract

Cosmological Birefringence (CB), a rotation of the polarization plane of radiation coming to us from distant astrophysical sources, may reveal parity violation in either the electromagnetic or gravitational sectors of the fundamental interactions in nature. Until only recently this phenomenon could be probed with only radio observations or observations at UV wavelengths. Recently, there is a substantial effort to constrain such non-standard models using observations of the rotation of the polarization plane of cosmic microwave background (CMB) radiation. This can be done via measurements of the $B$-modes of the CMB or by measuring its TB and EB correlations which vanish in the standard model. In this paper we show that $EB$ correlations-based estimator is the best for upcoming polarization experiments. The $EB$ based estimator surpasses other estimators because it has the smallest noise and of all the estimators is least affected by systematics. Current polarimeters are optimized for the detection of $B$-mode polarization from either primordial gravitational waves or by large scale structure via gravitational lensing. In the paper we also study optimization of CMB experiments for the detection of cosmological birefringence, in the presence of instrumental systematics, which by themselves are capable of producing $EB$ correlations; potentially mimicking CB.