Large-Nightmare Dark Matter

Abstract

A dark QCD sector is a relatively minimal extension of the Standard Model (SM) that admits Dark Matter (DM) candidates but requires no portal to the visible sector beyond gravitational interactions: A ’nightmare scenario’ for DM detection. We consider a secluded dark sector containing a single flavor of light, vector-like dark quark gauged under SU(N). In the large-N limit, this single-flavor theory becomes highly predictive, generating two DM candidates whose masses and dynamics are described by few parameters: A light quark-antiquark bound state, the dark analog of the η′ meson, and a heavy bound state of N quarks, the dark analog of the Δ++ baryon. We show that the latter may freeze-in with an abundance independent of the confinement scale, forming DM-like relics for N≲10, while the former may generate DM via cannibalization and freeze-out. We study the interplay of this two-component DM system and determine the characteristic ranges of the confinement scale, dark-visible sector temperature ratio, and N that admit non-excluded DM, once the effects of self-interaction constraints and bounds on effective degrees of freedom at the BBN and CMB epochs are included.