Distinguishing standard reionization from dark matter models

TL;DR

This paper investigates how dark matter annihilation impacts the CMB polarization spectrum and assesses whether these effects can be distinguished from standard reionization models with current and future observations.

Contribution

It introduces a detailed analysis of dark matter annihilation effects on reionization and CMB polarization, comparing them with standard models to evaluate observational distinguishability.

Findings

Dark matter halos at z<60 affect low multipoles in EE spectrum.

High redshift dark matter annihilation influences higher multipoles.

Current observations can partially distinguish dark matter effects from standard reionization.

Abstract

The Wilkinson Microwave Anisotropy Probe (WMAP) experiment has detected reionization at the $5.5 \sigma$ level and has reported a mean optical depth of $0.088 \pm 0.015$. A powerful probe of reionization is the large-angle $EE$ polarization power spectrum, which is now (since the first five years of data from WMAP) cosmic variance limited for $2\le l \le6$. Here we consider partial reionization caused by WIMP dark matter annihilation, and calculate the expected polarization power spectrum. We compare the dark matter models with a standard 2-step reionization theory, and examine whether the models may be distinguished using current, and future CMB observations. We consider dark matter annihilation at intermediate redshifts ($z<60$) due to halos, as well as annihilation at higher redshifts due to free particles. In order to study the effect of high redshift dark matter annihilation on CMB power spectra, it is essential to include the contribution of residual electrons (left over from recombination) to the ionization history. Dark matter halos at redshifts $z<60$ influence the low multipoles $l<20$ in the $EE$ power spectrum, while the annihilation of free particle dark matter at high redshifts $z>100$ mainly affects multipoles $l>10$.