A Minimal Asymmetric Dark Matter Model with Higgs-Portal Mediation A GeV-Scale Counterpart to Visible Matter

We present a minimal asymmetric dark matter model in which the dark sector contains astable neutral Dirac fermion X carrying a conserved dark number and a real scalar mediatorϕ coupled to the Standard Model through a Higgs portal. Motivated by the observedrelation ΩDM/Ωb ≃ 5.4, we consider the case in which the dark and baryonic asymmetriesare of comparable order, implying a natural dark matter mass near the GeV scale. Weintroduce an explicit effective asymmetry-transfer operator, formulate the correspondingBoltzmann description for the symmetric and asymmetric components, and discuss the roleof the scalar mediator in depleting the symmetric relic population. We further comment onHiggs-portal phenomenology and benchmark parameter ranges consistent with the minimalframework. The model is intended as a phenomenological benchmark rather than a completeultraviolet completion, but it illustrates how dark matter may arise as a cold, stable, massivecounterpart to visible matter with a shared cosmological origin.