Axion production and CMB spectral distortion in cosmological tangled magnetic field

TL;DR

This paper investigates how axion production and magnetic field damping before recombination contribute to CMB spectral distortions, providing new constraints on axion properties and magnetic field scales.

Contribution

It analyzes the relative impact of axion production and magnetic damping on CMB μ distortion, deriving new bounds on axion parameters and magnetic field scales.

Findings

Axion contribution to μ distortion is subdominant compared to magnetic damping.

Derived upper limit on magnetic field strength: B_0 ≤ 8.5×10^{-8} G.

Forecasted PIXIE/PRISM sensitivity to μ distortion.

Abstract

Axion production due to photon-axion mixing in tangled magnetic field(s) prior to recombination epoch and magnetic field damping can generate cosmic microwave background (CMB) spectral distortions. In particular, contribution of both processes to CMB $\mu$ distortion in the case of resonant photon-axion mixing is studied. Assuming that magnetic field power spectrum is approximated by a power law $P_B(k)\propto k^n$ with spectral index $n$, it is shown that for magnetic field cut-off scales $172.5$ pc $\leq \lambda_B\leq 4\times 10^3$ pc, axion contribution to CMB $\mu$ distortion is subdominant in comparison with magnetic field damping in the cosmological plasma. Using COBE upper limit on $\mu$ and for magnetic field scale $\lambda_B\simeq 415$ pc, weaker limit in comparison with other studies on the magnetic field strength ($B_0\leq 8.5\times 10^{-8}$ G) up to a factor 10 for the DFSZ axion model and axion mass $m_a\geq 2.6\times 10^{-6}$ eV is found. A forecast for the expected sensitivity of PIXIE/PRISM on $\mu$ is also presented.