Self-annihilating dark matter and the CMB: reionizing the Universe and constraining cross sections

TL;DR

Self-annihilating dark matter can significantly alter the early universe's ionization history, affecting CMB observations and allowing constraints on particle properties, with current data already limiting some models.

Contribution

This work summarizes recent progress in understanding how self-annihilating WIMP dark matter impacts recombination and CMB spectra, providing new bounds on dark matter particle parameters.

Findings

WMAP5 data constrains dark matter models explaining cosmic positron/electron anomalies

Planck has potential to detect signals from certain WIMP models

Dark matter annihilation influences the ionization history before galaxy formation

Abstract

I summarize the recent advances in determining the effects of self-annihilating WIMP dark matter on the modification of the recombination history, at times earlier than the formation of astrophysical objects. Depending on mass and self-annihilation cross section, WIMP DM can reproduce sizable amounts of the total free electron abundance at z > 6; as known, this affects the CMB temperature and polarization correlation spectra, and can be used to place stringent bounds in the particle mass vs cross-section plane. WMAP5 data already strongly disfavor the region capable to explain the recent cosmic positron and electrons anomalies in terms of DM annihilation, whereas in principle the Planck mission has the potential to see a signal produced by a candidate laying in that region, or from WIMPs with thermal annihilation cross-sections <sv>=3e-26 cm3/s and masses below 50 GeV.