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 $\tilde{\rho }\to \tilde{\pi }\tilde{\pi }\to 4V$ and from $CP$-violating pseudoscalar hypermeson decays of the form $\tilde{\eta }\to \tilde{\pi }\tilde{\pi }\to 4V$. The latter are sensitive to the vacuum angle $\tilde{\theta }$ 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 $\tilde{\theta }$. 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.

• Received 4 April 2018

DOI:https://doi.org/10.1103/PhysRevD.98.015028

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society