Constraining Ultralight ALP Dark Matter in Light of Cosmic Birefringence

TL;DR

This paper investigates whether ultralight axion-like particles (ALPs) can explain the observed cosmic birefringence, finding that late-universe clustering ALPs are incompatible with the observed signals due to coupling constraints.

Contribution

It provides new constraints on ALP dark matter models in the mass range $10^{-25}$ to $10^{-23}$ eV, considering nonlinear clustering and washout effects on CMB polarization.

Findings

ALPs with $10^{-25}$ eV $ o 10^{-23}$ eV cannot explain static birefringence.

Washout effects impose lower limits on ALP-photon coupling.

Rapid oscillations of higher-mass ALPs prevent them from explaining static birefringence.

Abstract

Cosmic birefringence, the observed rotation of the polarization plane of the cosmic microwave background (CMB), serves as a compelling probe for parity-violating physics beyond the Standard Model. This study explores the potential of ultralight axion-like particle (ALP) dark matter to explain the observed cosmic birefringence in the CMB. We focus on the previously understudied mass range of $10^{-25}$ eV to $10^{-23}$ eV, where ALPs start to undergo nonlinear clustering in the late universe. Our analysis incorporates recent cosmological constraints and considers the washout effect on CMB polarization. We find that for models with ALP masses $10^{-25}$ eV $\lesssim m_\phi \lesssim 10^{-23}$ eV and birefringence arising from late ALP clustering, the upper limit on the ALP-photon coupling constant, imposed by the washout effect, is stringently lower than the coupling required to account for the observed static cosmic birefringence signal. This discrepancy persists regardless of the ALP fraction in dark matter. Furthermore, considering ALPs with masses $m_\phi\gtrsim$ $10^{-23}$ eV cannot explain static birefringence due to their rapid field oscillations, our results indicate that, all ALP dark matter candidates capable of nonlinear clustering in the late universe and thus contributing mainly to the rotation angle of polarized photons, are incompatible with explaining the static cosmic birefringence signal observed in Planck and WMAP data.