Grand Unification, Dark Matter, Baryon Asymmetry, and the Small Scale Structure of the Universe

TL;DR

The paper tackles linking gauge coupling unification, the baryon asymmetry, and small-scale structure within a minimal GUT framework. It proposes a TeV-scale Higgsino messenger whose non-thermal decays generate a GeV-scale dark matter and transfer the baryon asymmetry to the SM via B-L dynamics, yielding the relation $Omega_DM/Omega_b \approx 5$ that fixes $m_DM \approx 1.5$ GeV. The predicted free-streaming scale is of order $0.1$ Mpc, derived from the non-thermal momentum distribution of DM produced at decay, consistent with Lyman-α constraints and potentially mitigating small-scale CDM tensions. Gauge coupling unification remains a key motivation, placing the messenger around TeV and the GUT scale at $M_GUT \sim 10^{14}$ GeV, with collider discovery prospects for the Higgsino being challenging.

Abstract

We consider a minimal grand unified model where the dark matter arises from non-thermal decays of a messenger particle in the TeV range. The messenger particle compensates for the baryon asymmetry in the standard model and gives similar number densities to both the baryon and the dark matter. The non-thermal dark matter, if massive in the GeV range, could have a free-streaming scale in the order of 0.1 Mpc and potentially resolve the discrepancies between observations and the LCDM model on the small scale structure of the Universe. Moreover, a GeV scale dark matter naturally leads to the observed puzzling proximity of baryonic and dark matter densities. Unification of gauge couplings is achieved by choosing a "Higgsino" messenger.