Two coincidences are a clue: Probing a GeV-scale dark QCD sector

The similarity between the dark matter and baryon energy densities suggests an existence of a dark sector analogous to QCD. In addition, small-scale structure anomalies can be addressed by dark matter self-interactions with cross sections comparable to those of QCD. Both observations point toward a GeV-scale dark QCD sector. Motivated by these two coincidences, we investigate the parameter space of a distinctive chiral dark QCD model featuring a MeV-scale dark photon with axial-vector couplings. We also discuss a possible third coincidence associated with the latest measurement of $N_{\rm eff}$. Current constraints leave a finite and testable region of parameter space that can be probed by future experiments such as the Gamma Factory.