Impact of Dark Matter Annihilation on the High-Redshift Intergalactic Medium

TL;DR

This paper investigates how dark matter annihilation, especially considering particle clumping, can influence the temperature and ionization state of the early universe's intergalactic medium, affecting observable signals like the 21-cm line.

Contribution

It introduces the impact of dark matter clumping on energy injection and its effects on high-redshift gas temperature and reionization, a novel aspect in the study of dark matter's cosmological role.

Findings

Dark matter annihilation can significantly heat the intergalactic medium at high redshifts.

Energy injection from dark matter contributes to the electron optical depth.

Dark matter alone cannot fully reionize the universe.

Abstract

We reexamine the impact of dark matter (DM) annihilation on the intergalactic medium, taking into account the clumping of DM particles. We find that energy injection from the annihilation of the thermal relic DM particles may significantly raise the gas temperature at high redshifts and leave a strong imprint on the cosmological 21-cm signal, provided the particle mass is below ~1 TeV. Further, we find that while the energy injection from DM annihilation could not alone complete the reionization of the Universe, it could make a significant contribution to the electron optical depth.