Bounds and detection of MeV-scale dark matter annihilation to neutrinos

TL;DR

This paper derives new constraints on MeV-scale dark matter annihilation to neutrinos by considering non-standard scenarios and entropy effects, showing that some bounds surpass current limits and assessing future detector sensitivities.

Contribution

It introduces a comprehensive analysis of relic dark matter annihilation after neutrino decoupling, incorporating entropy injection and nonthermal neutrino energy release effects.

Findings

Constraints on annihilation cross section can be stronger than current bounds.

Lower bounds on dark matter mass are inconclusive with recent data.

Upcoming neutrino detectors will probe significant parameter space.

Abstract

Current and most upcoming neutrino detectors can only reach a dark matter annihilation cross section to neutrinos larger than the standard freeze-out value, but they open intriguing detection avenues for non-standard dark matter paradigms. An important corollary of these non-standard scenarios is relic dark matter annihilation after neutrino decoupling, which was previously overlooked in constraining MeV-scale dark matter. However, by combining the contributions from entropy injection during neutrino decoupling and from nonthermal neutrino energy release after decoupling, we derive significant constraints on the annihilation cross section to neutrinos, which in some mass regimes become stronger than the current bounds. Furthermore, we find that the lower bounds on dark matter masses become inconclusive under the recent data releases from the DESI, SPT-3G, and ACT collaborations. These bounds determine the extent to which upcoming neutrino detectors will probe dark matter annihilation into neutrinos.