Axion production and CMB spectral distortion in cosmological tangled magnetic field

Damian Ejlli

doi:10.1140/epjc/s10052-015-3606-3

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.

Highlights

In the presence of a large scale magnetic field, cosmic microwave background (CMB) photons can in principle convert into axions or other similar particles due to their coupling with the magnetic field
It has been shown in Ref. [14] that a spatially varying stochastic magnetic field may significantly dissipate in the cosmological plasma prior to the recombination epoch
In this work we have considered the impact of spatially varying stochastic magnetic fields and resonant photon–axion mixing on the CMB μ distortion

Summary

Introduction

In the presence of a large scale magnetic field, CMB photons can in principle convert into axions or other similar particles due to their coupling with the magnetic field. As in the case of density perturbations in the primordial baryonic plasma suffering from Silk damping, we can expect that a spatially varying magnetic field can couple to the baryon plasma and dissipate energy This would eventually lead to the damping of the primordial magnetic field spectrum on different scales [12,13]. A distinguishing feature of a non-homogeneous magnetic field in comparison with an uniform field is that the former can have an impact on the CMB by distorting its spectrum. For an early treatment of CMB spectral distortion see Refs. [15,16]; for further developments see Refs. [17,18,19,20,21,22,23,24,25,26], and for production mechanisms of spectral distortions see Refs. [27,28,29,30]

Dissipation of tangled magnetic field

Axion contribution to spectral distortion

Summary