Dark-sector seeded solution to the strong CP problem

We propose a novel realization of the Nelson-Barr mechanism seeded by a dark sector containing scalars and vectorlike quarks. Charge parity (CP) and a Z8 symmetry are spontaneously broken by the complex vacuum expectation value of a singlet scalar, leaving a residual Z2 symmetry that stabilizes dark matter (DM). A complex Cabibbo-Kobayashi-Maskawa matrix arises via one-loop corrections to the quark mass matrix mediated by the dark sector. In contrast with other proposals where nonzero contributions to the strong CP phase arise at the one-loop level, in our case this occurs only at two loops, enhancing naturalness. Our scenario also provides a viable weakly interacting massive particle scalar DM candidate.

Automated summary

We propose a novel realization of the Nelson-Barr mechanism using a dark sector consisting of scalars and vectorlike quarks. Through spontaneous breaking of charge parity (CP) and a Z8 symmetry by the complex vacuum expectation value of a singlet scalar, a residual Z2 symmetry is left to stabilize dark matter (DM). A complex Cabibbo-Kobayashi-Maskawa matrix is generated through one-loop corrections mediated by the dark sector, with nonzero contributions to the strong CP phase occurring only at the two-loop level in our case, enhancing naturalness. Our scenario also presents a viable Weakly Interacting Massive Particle (WIMP) scalar DM candidate.