Detection of isotropic cosmic birefringence and its implications for axionlike particles including dark energy
Tomohiro Fujita, Kai Murai, Hiromasa Nakatsuka, Shinji Tsujikawa
Abstract
We investigate the possibility that axionlike particles (ALPs) with various potentials account for the isotropic birefringence recently reported by analyzing the Planck 2018 polarization data. For the quadratic and cosine potentials, we obtain lower bounds on the mass, coupling constant to photon $g$, abundance and equation of state of the ALP to produce the observed birefringence. Especially when the ALP is responsible for dark energy, it is possible to probe the tiny deviation of dark energy equation of state from $\ensuremath{-}1$ through the cosmic birefringence. We also explore ALPs working as early dark energy (EDE), which alleviates the Hubble tension problem. Since the other parameters are limited by the EDE requirements, we narrow down the ALP-photon coupling to ${10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}\ensuremath{\lesssim}g\ensuremath{\lesssim}{10}^{\ensuremath{-}16}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}1}$ for the decay constant $f={M}_{\mathrm{pl}}$. Therefore, the Hubble tension and the isotropic birefringence imply that $g$ is typically the order of ${f}^{\ensuremath{-}1}$, which is a nontrivial coincidence.