Theta in new QCD-like sectors

Abstract

New QCD-like "hypercolor" sectors can generate a broad class of new signatures at hadron colliders and furnish a variety of dark matter candidates. Paired diboson resonances are a particularly important collider signature, arising both from CP-conserving vector hypermeson decays of the form ρ→ππ→4V and from CP-violating pseudoscalar hypermeson decays of the form η→ππ→4V. The latter are sensitive to the vacuum angle θ in the hypercolor sector. We study single- and paired-diboson resonance signatures in final states involving gluons and photons at the LHC and a future 100 TeV pp collider, illustrating the discovery potential at both colliders in simple benchmark models. We also describe some of the theoretical and cosmological consequences of θ. If CP-violating hypermeson decays are observable at hadron colliders, ordinary QCD must have an axion. Such scenarios also provide a natural setting for a dark pion component of dark matter, with its relic abundance set by CP-violating annihilations. If the new vacuum angle is relaxed to zero by a dark axion, the relic density can instead be a mixture of axions and dark axions. Overproduction of dark axions is most easily avoided if the Universe underwent a period of early matter domination.