CMB anisotropies generated by a stochastic background of primordial magnetic fields with non-zero helicity

TL;DR

This paper investigates how primordial magnetic fields with helicity influence CMB anisotropies, providing exact calculations of their effects on temperature, polarization, and parity-odd correlations, up to high multipoles.

Contribution

It offers the first detailed computation of the impact of helical primordial magnetic fields on CMB anisotropies, including parity-odd correlators, with exact expressions for all perturbation modes.

Findings

Helical magnetic fields induce parity-odd TB and EB correlations in the CMB.

Including helicity modifies the CMB power spectra up to multipoles of about 1000.

Exact expressions for the energy-momentum tensor components with helicity are derived.

Abstract

We consider the impact of a stochastic background of primordial magnetic fields with non-vanishing helicity on CMB anisotropies in temperature and polarization. We compute the exact expressions for the scalar, vector and tensor part of the energy-momentum tensor including the helical contribution, by assuming a power-law dependence for the spectra and a comoving cutoff which mimics the damping due to viscosity. We also compute the parity-odd correlator between the helical and non-helical contribution which generate the TB and EB cross-correlation in the CMB pattern. We finally show the impact of including the helical term on the power spectra of CMB anisotropies up to multipoles with ell ~ O(10^3)$.