Light thermal relics enabled by a second Higgs

TL;DR

This paper proposes a minimal model with a second Higgs doublet acting as a light mediator, enabling sub-GeV thermal relic dark matter to annihilate via a new portal, with observable implications for Higgs physics and gamma-ray signals.

Contribution

Introduction of a light two-Higgs-doublet portal model for sub-GeV dark matter with a UV-complete framework and testable predictions.

Findings

Light mediator enables sub-GeV dark matter annihilation.

Model affects Higgs physics and muon g-2.

Future gamma-ray telescopes can detect dark matter signals.

Abstract

Sub-GeV thermal relic dark matter typically requires the existence of a light mediator particle. We introduce the light two-Higgs-doublet portal, illustrated by a minimal UV-complete model for sub-GeV dark matter with kinematically forbidden annihilations into leptons. All new physics states in this scenario lie at or below the electroweak scale, affecting Higgs physics, the muon anomalous magnetic moment and potentially neutrino masses. Observation of radiative dark matter annihilation by future MeV gamma-ray telescopes would be key to unambiguously identify the scenario.