Impact of Sommerfeld enhancement on helium reionization via WIMP dark matter

TL;DR

This paper investigates how Sommerfeld-enhanced dark matter annihilation influences helium reionization, finding significant enhancement in signatures but no major shift in reionization timing under CMB constraints.

Contribution

It provides the first calculation of Sommerfeld-enhanced dark matter annihilation effects during helium reionization, highlighting the potential for indirect detection signatures.

Findings

Enhancement of annihilation signatures by 1-2 orders of magnitude.

No significant shift in helium reionization epoch under CMB constraints.

Dark matter contribution is difficult to distinguish from astrophysical sources.

Abstract

Dark matter annihilation can have a strong impact on many astrophysical processes in the Universe. In the case of Sommerfeld-enhanced annihilation cross sections, the annihilation rates are enhanced at late times, thus enhancing the potential annihilation signatures. We here calculate the Sommerfeld-enhanced annihilation signatures during the epoch of helium reionization, the epoch where helium becomes fully ionized due to energetic photons. When considering the upper limits on the energy injection from the CMB, we find that the resulting abundance of He$^{++}$ becomes independent of the dark matter particle mass. The resulting enhancement compared to a standard scenario is thus 1-2 orders of magnitude higher. For realistic scenarios compatible with CMB constraints, there is no significant shift in the epoch of helium reionization, which is completed between redshifts $3$ and $4$. While it is thus difficult to disentangle dark matter annihilation from astrophysical contributions (active galactic nuclei), a potential detection of dark matter particles and its interactions using the Large Hadron Collider (LHC) would allow one to quantify the dark matter contribution.