Astrophysical Signatures of Secluded Dark Matter

TL;DR

This paper investigates astrophysical signals of secluded WIMP dark matter models, highlighting how light mediators can enhance annihilation signals, especially positron excesses, without needing astrophysical boost factors.

Contribution

It introduces the concept of enhanced annihilation via metastable mediators in secluded dark matter models, emphasizing the role of light MeV-scale vectors and bound states.

Findings

Enhanced positron flux from dark matter annihilation.

Significant cross section increase in galactic halo.

Potential explanation for positron excess without boost factors.

Abstract

We analyze the indirect astrophysical signatures of secluded models of WIMP dark matter, characterized by a weak-scale rate for annihilation into light MeV-scale mediators which are metastable to decay into Standard Model states. Such scenarios allow a significant enhancement of the annihilation cross section in the galactic halo relative to its value at freeze-out, particularly when the mediator is light enough for this process to proceed through radiative capture to a metastable `WIMP-onium' bound state. For MeV-scale vector mediators charged under a hidden U(1)' gauge group, the enhanced annihilation rate leads predominantly to a sizable excess positron flux, even in the absence of astrophysical boost factors.