Description
Author and Presenter: Raymond Co
Abstract: We investigate the field dynamics of the ZN QCD axion, a variant of the QCD axion that couples to N copies of the Standard Model. Contributions from N − 1 dark sectors and the visible sec- tor QCD lead to an exponentially suppressed axion mass and a time-dependent periodic potential. The potential minimum is at θ = π before the QCD phase transition. After the phase transition, this point becomes a hilltop and multiple minima develop with only one of them actually solving the strong CP problem. The resultant non-trivial field dynamics, such as rotations over potential barriers and oscillations from the hilltop, give rise to parametric resonance production of axions. We perform the first lattice simulations of the axion field evolving through the QCD phase transi- tion in an expanding universe. We find that nonlinear effects significantly impact the axion’s relic abundance and final settling point. We show the viable parameter space in which this light QCD axion can simultaneously constitute all of dark matter and solve the strong CP problem.
