Cross-Correlation of Cosmological Birefringence with CMB Temperature

TL;DR

This paper explores the potential correlation between cosmological birefringence and CMB temperature anisotropies, proposing that such a correlation could reveal properties of new physics fields and improve detection sensitivity.

Contribution

It introduces the concept of cross-correlation between CB-induced polarization rotation and CMB temperature, providing a method to distinguish between different theoretical models of CB.

Findings

Cross-correlation exists in quintessence scenarios.

No correlation in massless spectator field scenarios.

Measurement of this correlation can enhance sensitivity to CB signals.

Abstract

Theories for new particle and early-Universe physics abound with pseudo-Nambu-Goldstone fields that arise when global symmetries are spontaneously broken. The coupling of these fields to the Chern-Simons term of electromagnetism may give rise to cosmological birefringence (CB), a frequency-independent rotation of the linear polarization of photons as they propagate over cosmological distances. Inhomogeneities in the CB-inducing field may yield a rotation angle that varies across the sky. Here we note that such a spatially-varying birefringence may be correlated with the cosmic microwave background (CMB) temperature. We describe quintessence scenarios where this cross-correlation exists and other scenarios where the scalar field is simply a massless spectator field, in which case the cross-correlation does not exist. We discuss how the cross-correlation between CB-rotation angle and CMB temperature may be measured with CMB polarization. This measurement may improve the sensitivity to the CB signal, and it can help discriminate between different models of CB.