Cosmic Birefringence from Neutrino and Dark Matter Asymmetries

Understand

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.