CMB anisotropies from patchy reionisation and diffuse Sunyaev-Zel'dovich effects

TL;DR

This paper provides a comprehensive relativistic analysis of CMB anisotropies caused by patchy reionisation and diffuse Sunyaev-Zel'dovich effects, highlighting their impact on temperature and polarization spectra, including B-modes comparable to primordial gravitational waves.

Contribution

It introduces a complete second-order perturbation theory treatment of CMB anisotropies from reionisation and SZ effects, including their correlations, using the numerical Boltzmann code SONG.

Findings

Diffuse SZ effects contribute significantly to CMB anisotropies.

B-modes at intermediate scales are comparable to those from primordial gravitational waves.

The approach enables reliable estimates of temperature and polarization power spectra.

Abstract

Anisotropies in the Cosmic Microwave Background (CMB) can be induced during the later stages of cosmic evolution, and in particular during and after the Epoch of Reionisation. Inhomogeneities in the ionised fraction, but also in the baryon density, in the velocity fields and in the gravitational potentials are expected to generate correlated CMB perturbations. We present a complete relativistic treatment of all these effects, up to second order in perturbation theory, that we solve using the numerical Boltzmann code SONG. The physical origin and relevance of all second order terms are carefully discussed. In addition to collisional and gravitational contributions, we identify the diffuse analogue of the blurring and kinetic Sunyaev-Zel'dovich (SZ) effects. Our approach naturally includes the correlations between the imprint from patchy reionisation and the diffuse SZ effects thereby allowing us to derive reliable estimates of the induced temperature and polarisation CMB angular power spectra. In particular, we show that the B-modes generated at intermediate length-scales (l~100) have the same amplitude as the B-modes coming from primordial gravitational waves with a tensor-to-scalar ratio r=10^{-4}.