Cosmic Birefringence from Neutrino and Dark Matter Asymmetries

TL;DR

This paper investigates whether cosmic birefringence observed in CMB polarization can be explained by interactions involving neutrino and dark matter asymmetries, providing new theoretical insights and examining observational constraints.

Contribution

It introduces corrected formulae for cosmic birefringence and links the effect to neutrino and dark matter asymmetries, exploring parameter spaces consistent with recent measurements.

Findings

Neutrino asymmetry can explain the observed birefringence within certain parameters.

Dark matter asymmetry models with specific masses are compatible with polarization rotation data.

Constraints from CMB spectra and direct detection limit the viable parameter space.

Abstract

In light of the recent measurement of the nonzero Cosmic Microwave Background (CMB) polarization rotation angle from the Planck 2018 data, we explore the possibility that such a cosmic birefringence effect is induced by coupling a fermionic current with photons via a Chern-Simons-like term. We begin our discussion by rederiving the general formulae of the cosmic birefringence angle with correcting a mistake in the previous study. We then identify the fermions in the current as the left-handed electron neutrinos and asymmetric dark matter (ADM) particles, since the rotation angle is sourced by the number density difference between particles and antiparticles. For the electron neutrino case, with the value of the degeneracy parameter $\xi_{\nu_e}$ recently measured by the EMPRESS survey, we find a large parameter space which can explain the CMB photon polarization rotations. On the other hand, for the ADM solution, we consider two benchmark cases with $M_\chi = 5$~GeV and 5~keV. The former is the natural value of the ADM mass if the observed ADM and baryon asymmetry in the Universe are produced by the same mechanism, while the latter provides a warm DM candidate. In addition, we explore the experimental constraints from the CMB power spectra and the DM direct detections.