Testing Parity-Violating Mechanisms with Cosmic Microwave Background Experiments

TL;DR

This paper investigates how to distinguish between two physical mechanisms, chiral gravity and cosmological birefringence, that produce parity-violating correlations in the CMB, using their distinct signatures in TB and EB spectra.

Contribution

It introduces a detailed analysis of TB-EB covariances and demonstrates that the effects of the two mechanisms are highly orthogonal, enabling their differentiation with high signal-to-noise data.

Findings

Chiral gravity and birefringence effects are highly orthogonal in CMB signals.

High S/N detection of TB/EB correlations can distinguish the mechanisms.

Appendix compares sensitivities of BB, TB, and EB signals for gravitational-wave detection.

Abstract

Chiral gravity and cosmological birefringence both provide physical mechanisms to produce parity-violating TB and EB correlations in the cosmic microwave background (CMB) temperature/polarization. Here, we study how well these two mechanisms can be distinguished if non-zero TB/EB correlations are found. To do so, we evaluate the correlation matrix, including new TB-EB covariances. We find that the effects of these two mechanisms on the CMB are highly orthogonal, and can thus be distinguished fairly well in case of a high--signal-to-noise detection of TB/EB correlations. An Appendix evaluates the relative sensitivities of the BB, TB, and EB signals for detecting a chiral gravitational-wave background.