Prospects for Probing Sub-GeV Leptophilic Dark Matter with the Future VLAST

TL;DR

VLAST's advanced sensitivity in the MeV-GeV range enables it to explore sub-GeV leptophilic dark matter, especially near resonance regions, surpassing current detection methods and filling the MeV gap in gamma-ray observations.

Contribution

This paper demonstrates VLAST's potential to detect sub-GeV leptophilic dark matter, particularly in resonance regions where other methods are less effective.

Findings

VLAST can probe the resonance region of sub-GeV leptophilic DM.

Resonance regions remain viable despite constraints from relic density and CMB.

VLAST outperforms existing instruments in detecting certain DM parameter spaces.

Abstract

The proposed Very Large Area Space Telescope (VLAST), with its expected unprecedented sensitivity in the MeV-GeV range, can also address the longstanding "MeV Gap" in gamma-ray observations. We explore the capability of VLAST to detect sub-GeV leptophilic dark matter (DM) annihilation, focusing on scalar and vector mediators and emphasizing the resonance region where the mediator mass is approximately twice the DM mass. While $s$-wave annihilation is tightly constrained by relic density and cosmic microwave background observations, $p$-wave and mixed $(s+p)$-wave scenarios remain viable, particularly near resonance. Additionally, direct detection experiments, especially those probing DM-electron scattering, significantly constrain nonresonance parameter space but are less effective in the resonance regime. VLAST can uniquely probe this surviving region, outperforming existing and planned instruments, and establishing itself as a crucial tool for indirect detection of thermal relic DM.