Imprints of the post-recombination dissipation of helical magnetic field on the Cosmic Microwave Background Radiation

Abstract

Astrophysical magnetic fields decay primarily via two processes namely, ambipolar diffusion and turbulence. Constraints on the strength and the spectral index of non-helical magnetic fields have been derived earlier in the literature through the effect of the above mentioned processes on the Cosmic Microwave Background (CMB) radiation. A helical component of the magnetic field is also produced in various models of magnetogenesis, which can explain larger coherence length magnetic field. In this study, we focus on studying the effects of post recombination decay of maximally helical magnetic fields through ambipolar diffusion and decaying magnetic turbulence and the impact of this decay on CMB. We find that helical magnetic fields lead to changes in the evolution of baryon temperature and ionization fraction which in turn lead to modifications in the CMB temperature and polarization anisotropy. These modifications are different from those arising due to non-helical magnetic fields with the changes dependent on the strength and the spectral index of the magnetic field power spectra.