Tangled magnetic fields and CMBR signal from reionization epoch

Abstract

We compute the secondary cosmic microwave background radiation (CMBR) anisotropy signal from the reionization of the Universe in the presence of tangled magnetic fields. We consider the tangled-magnetic-field-induced scalar, vector, and tensor modes for our analysis. The most interesting signal for [script-l]<~100 arises from tensor perturbations. In particular, we show that the enhancement observed by Wilkinson microwave anisotropy probe (WMAP) in the TE cross-correlation signal for [script-l]<~10 could be explained by tensor TE cross correlation from tangled magnetic fields generated during the inflationary epoch for magnetic field strength B0~=4.5×10-9 G and magnetic field power spectrum spectral index n~=-2.9. Alternatively, a mixture of tensor mode signal with primordial scalar modes gives weaker bounds on the value of the optical depth to the reionization surface, taureion: taureion=0.11±0.02. This analysis can also be translated to a limit on magnetic field strength of ~=5×10-9 G for wave numbers <~0.05 Mpc-1.