How Dark Matter Reionized The Universe

TL;DR

This paper investigates how dark matter annihilations could have significantly contributed to reionizing the universe by redshift z ~ 6, proposing a mechanism involving energetic electrons and gamma rays.

Contribution

It introduces a novel model where dark matter annihilations with electroweak scale masses drive the universe's reionization, aligning with recent cosmic ray observations.

Findings

Dark matter annihilations can produce sufficient ionization for reionization.

Electroweak scale dark matter candidates are viable for reionization.

Candidates explaining cosmic ray excesses also reionize the universe by z ~ 6.

Abstract

Although empirical evidence indicates that that the universe's gas had become ionized by redshift z ~ 6, the mechanism by which this transition occurred remains unclear. In this article, we explore the possibility that dark matter annihilations may have played the dominant role in this process. Energetic electrons produced in these annihilations can scatter with the cosmic microwave background to generate relatively low energy gamma rays, which ionize and heat gas far more efficiently than higher energy prompt photons. In contrast to previous studies, we find that viable dark matter candidates with electroweak scale masses can naturally provide the dominant contribution to the reionization of the universe. Intriguingly, we find that dark matter candidates capable of producing the recent cosmic ray excesses observed by PAMELA and/or ATIC are also predicted to lead to the full reionization of the universe by z ~ 6.