Ultra-Light Pion and Baryon WIMPzilla Dark Matter

Abstract: We consider a dark confining gauge theory with millicharged Ultra-Light Pions (ULP) and heavy baryons as dark matter candidates. The model simultaneously realizes the ultra-light (STrongly-interacting Ultralight Millicharged Particle or "STUMP") and superheavy ("WIMPzilla") dark matter paradigms, connected by the confinement scale of the dark QCD. It is a realization of millicharged ULDM, very unlike conventional axions, and exhibits a mass splitting between the charged and neutral pions. ULPs can easily provide the observed density of the dark matter, and be cosmologically stable, for a broad range of dark QCD scales and quark masses. The dark baryons, produced via gravitational particle production or via freeze-in, provide an additional contribution to the dark matter density. Dark matter halos and boson stars in this context are generically an admixture of the three pions and heavy baryons, leading to a diversity of density profiles. That opens up the accessible parameter space of the model compared with the standard millicharged DM scenarios and can be probed by future experiments. We briefly discuss additional interesting phenomenology, such as ULP electrodynamics, and Cosmic ULP Backgrounds.