Quentin Bonnefoy

The quantum chromodynamics (QCD) axion may solve the strong CP problem and explain the dark matter (DM) abundance of our Universe. The axion was originally proposed to arise as the pseudo-Nambu-Goldstone boson of global U(1)PQ Peccei-Quinn (PQ) symmetry breaking, but axions also arise generically in string theory as zero modes of higher-dimensional gauge fields. In this work we show that string theory axions behave fundamentally differently from field theory axions in the early Universe.

We study thermal production of dark matter (DM) in a realization of the minimal models of Bonnefoy et al. [Phys. Rev. Lett. 131, 221802 (2023)], where parity is used to solve the strong CP problem by transforming the entire Standard Model (SM) into a mirror copy. Although the mirror electron e′ is a good DM candidate, its viability is mired by the presence of the mirror up quark u′, whose abundance is intimately related to the e′ abundance and must be suppressed.

We propose theories of a complete mirror world with parity (P) solving the strong CP problem. P exchanges the entire standard model with its mirror copy. We derive bounds on the two new mass scales that arise: v′ where parity and mirror electroweak symmetry are spontaneously broken, and v3 where the color groups break to the diagonal strong interactions. The strong CP problem is solved even if v3≪v′, when heavy colored states at the scale v3 may be accessible at LHC and future colliders.