Comparable Dark Matter and Baryon energy densities from Dark Grand Unification

Abstract

We investigate a theory of $SU(9)$ dark grand unification, where dark matter consists of asymmetric dark baryons from the $Sp(4)_D$ dark QCD sector. By unifying the dark color gauge group with the Standard Model gauge group, the asymmetry generation in both sectors originates from a common process that preserves a $U(1)_{D-(B-L)}$ symmetry, resulting in comparable number densities. Furthermore, thanks to dark grand unification, the $Sp(4)_D$ dark QCD sector shares a similar matter content with the QCD sector, leading to comparable running of the gauge couplings from the scale as high as $10^{15}$ GeV. This predicts a dark color confinement scale and thus dark baryon masses around the GeV scale, comparable to visible baryon masses. Together with the similar number densities, the model provides an explanation for the observed similarity between the energy densities of dark matter and baryons, $\rho_D \approx 5\,\rho_B$. The model also features some novel phenomenology, including a GeV-scale flavored dark QCD sector with diquark dark baryons and light dark mesons. The interaction between the dark sector and the visible sector occurs via a new $Z'$ boson with a mass of $\mathcal{O}(10)$ TeV, which could be searched for at future hadron colliders. We also briefly discuss an $SU(8)$ dark grand unified theory featuring an $SU(3)_D$ dark QCD sector.