Surveying the theory space of pion dark matter

Abstract

We use a holographic model to survey the space of strongly coupled SU(Nc) gauge dynamics with QCD-like chiral symmetry breaking pattern for quarks in the fundamental representation. We systematically identify the light degrees of freedom (rho, sigma and pi mesons) that would make up the dark sector as a function of Nf, Nc and a common quark mass scale. We identify seven distinct effective theories that are of interest to explore and make a first summary of the expected dark matter phenomenology. Amongst our results we conclude that QCD-like models where the low energy theory is described purely in terms of pions struggle to generate a large enough Mpi/fpi value so these theories will need extra relic density generation mechanisms to be viable. The largest space of models (with an intermediate quark mass) have both the sigma and rho lying below 2 Mpi and are largely unexplored in the literature so far. Regions with just one of rho or sigma light are possible in constrained parameter regions. These states aid the pion relic density generation as needed for valid theories. The sigma always lies above the pi mass becoming degenerate with the pi in the extreme walking limit.