Dark Ultra-Light Scalars and Cosmic Parity Violation

TL;DR

This paper reviews how ultra-light scalar dark sector fields coupled via Chern-Simons terms can cause polarization rotation in the CMB, leading to observable parity-violating signals in B-mode polarization.

Contribution

It provides a detailed derivation of polarization rotation effects and summarizes potential signals in current and future CMB experiments.

Findings

Rotation induces B-mode polarization from E-modes

Creates parity-violating TB and EB correlations

Potential detectability in upcoming CMB observations

Abstract

If the dark sector of the Universe consists of ultra-light scalars, their coupling to photon via a Chern-Simons term would induce a rotation of the polarization plane of the cosmic microwave background (CMB). This rotation would convert E -mode polarization into B -mode polarization, resulting in new CMB BB correlation and parity-violating TB and EB cross correlations. We review the subject giving details about the derivation of the rotational effects and summarizing the possible signals in current and future CMB B-mode experiments.