Can primordial parity violation explain the observed cosmic birefringence?

TL;DR

This paper investigates whether primordial parity violation via chiral gravitational waves can explain the observed cosmic birefringence, concluding that it cannot due to overproduction of certain polarization signals.

Contribution

It provides a detailed analysis of primordial chiral gravitational waves as an explanation for cosmic birefringence, ruling out this scenario based on observational constraints.

Findings

Chiral gravitational waves overproduce B-mode polarization.

Primordial parity violation cannot explain the observed birefringence.

The scenario is inconsistent with current CMB polarization data.

Abstract

Recently, the cross-correlation between $E$- and $B$-mode polarization of the cosmic microwave background (CMB), which is well explained by cosmic birefringence with rotation angle $\beta\approx 0.3$ deg, has been found in CMB polarization data. We carefully investigate the possibility of explaining the observed $EB$ correlation by the primordial chiral gravitational waves (CGWs), which can be generated in the parity-violating theories in the primordial Universe. We found that the CGWs scenario does not work due to the overproduction of the $BB$ auto-correlation which far exceeds the observed one by SPTPol and POLARBEAR.