CMB with the background primordial magnetic field

TL;DR

This paper studies how primordial magnetic fields influence the cosmic microwave background, affecting peak positions and amplitudes, and explores implications for understanding the origin and evolution of these magnetic fields.

Contribution

It provides a detailed analysis of the effects of background primordial magnetic fields on CMB anisotropies and discusses constraints on their generation and evolution mechanisms.

Findings

Primordial magnetic fields increase the sound speed of the photon-baryon fluid.

They suppress the first peak of the CMB and shift peaks to larger scales.

Degeneracies exist between magnetic field parameters and standard cosmological parameters.

Abstract

We investigate the effects of the background primordial magnetic field (PMF) on the cosmic microwave background (CMB). The sound speed of the tightly coupled photon-baryon fluid is increased by the background PMF. The increased sound speed causes the odd peaks of the CMB temperature fluctuations to be suppressed and the CMB peak positions to be shifted to a larger scale. The background PMF causes a stronger decaying potential and increases the amplitude of the CMB. These two effects of the background PMF on a smaller scale cancel out, and the overall effects of the background PMF are the suppression of the CMB around the first peak and the shifting of peaks to a large scale. We also discuss obtaining information about the PMF generation mechanisms, and we examine the nonlinear evolution of the PMF by the constraint on the maximum scale for the PMF distributions. Finally, we discuss degeneracies between the PMF parameters and the standard cosmological parameters.