Bounds on QCD axion mass and primordial magnetic field from CMB $\mu$-distortion

TL;DR

This paper derives bounds on QCD axion mass and primordial magnetic fields from CMB spectral distortion measurements, providing new constraints and forecasts for future experiments like PIXIE/PRISM.

Contribution

It introduces novel bounds on axion mass and magnetic field strength using CMB $bc$-distortion data, and forecasts future detection prospects.

Findings

Upper limit on axion mass: $m_a \u2264 4.8 imes 10^{-5}$ eV.

Magnetic field strength constraints: $B ew 46$ nG for axion mass from ADMX.

Future experiments could detect axions with masses $2-3$ bc eV under certain magnetic field assumptions.

Abstract

The oscillation of the CMB photons into axions can cause CMB spectral distortion in the presence of large scale magnetic field. With the COBE limit on the $\mu$ parameter and a homogeneous magnetic field with strength $B\lesssim 3.2$ nG at the horizon scale, an upper limit on the axion mass is found to be, $m_a\lesssim 4.8\times 10^{-5}$ eV for the KSVZ axion model. On the other hand, using the value of excluded axion mass $m_a\simeq 3.5\times 10^{-6}$ eV from the ADMX experiment together with the COBE bound on $\mu$, is found $B\simeq 46$ nG for the KSVZ axion model and $B\simeq 130$ nG for DFSZ axion model, for a homogeneous magnetic field with coherence length at the present epoch $\lambda_B\simeq 1.3$ Mpc. Forecast on $B$ and $m_a$ for PIXIE/PRISM expected sensitivity on $\mu$ are derived. If CMB $\mu$ distortion would be detected by the future space missions PIXIE/PRISM and assuming that the strength of the large scale magnetic field is close to its canonical value, $B\simeq 1-3$ nG, axions in the mass range $2\, \mu$eV - $3\, \mu$eV would be potential candidates of CMB $\mu$-distortion.