Detection of isotropic cosmic birefringence and its implications for axion-like particles including dark energy

TL;DR

This paper explores how axion-like particles could explain cosmic birefringence and dark energy, providing bounds on their properties and implications for the Hubble tension.

Contribution

It analyzes Planck data to constrain ALP parameters and links cosmic birefringence with dark energy and early dark energy models.

Findings

Bounds on ALP mass, coupling, and abundance for observed birefringence.

ALPs as dark energy can reveal deviations in dark energy equation of state.

ALPs as early dark energy help address the Hubble tension.

Abstract

We investigate the possibility that axion-like 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 $-1$ 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 $10^{-19}\, {\rm GeV}^{-1}\lesssim g\lesssim 10^{-16}\, {\rm GeV}^{-1}$ for the decay constant $f=M_\mathrm{pl}$. Therefore, the Hubble tension and the isotropic birefringence imply that $g$ is typically the order of $f^{-1}$, which is a non-trivial coincidence.