Surveying the theory space of pion dark matter
摘要
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 (ρ, σ and π 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 Mπ/fπ 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 σ and ρ lying below 2Mπ and are largely unexplored in the literature so far. Regions with just one of ρ or σ light are possible in constrained parameter regions. These states aid the pion relic density generation as needed for valid theories. The σ always lies above the π mass becoming degenerate with the π in the extreme walking limit.