Axion misalignment driven to the hilltop

Abstract The QCD axion serves as a well-motivated dark matter candidate and the misalignment mechanism is known to reproduce the observed abundance with a decay constant f a ≃ O $$ \mathcal{O} $$ (1012) GeV for a misalignment angle θ mis ≃ O $$ \mathcal{O} $$ (1). While f a ≪ 1012 GeV is of great experimental interest, the misalignment mechanism requires the axion to be very close to the hilltop, i.e. θ mis ≃ π. This particular choice of θ mis has been understood as fine-tuning the initial condition. We offer a dynamical explanation for θ mis ≃ π in a class of models. The axion dynamically relaxes to the minimum of the potential by virtue of an enhanced mass in the early universe. This minimum is subsequently converted to a hilltop because the CP phase of the theory shifts by π when one contribution becomes subdominant to another with an opposite sign. We demonstrate explicit and viable examples in supersymmetric models where the higher dimensional Higgs coupling with the inflaton naturally achieves both criteria. Associated phenomenology includes a strikingly sharp prediction of 3 × 109 GeV ≲ f a ≲ 1010 GeV and the absence of isocurvature perturbation.

Abstract licence: CC BY

A person counts once a day per paper. We keep no cookie and no address: a reader is a hash that changes every day. Any month under five reads shows no number.