HEP Theory Seminar

Axion dark matter with thermal friction

by Hyeonseok Seong (DESY)


Cosmological evolution of axion field could be significantly modified in the presence of a thermalized hidden sector. We study pure hidden Yang-Mills (YM) gauge fields as an example, which generates friction through the sphaleron processes. The analytic solution of the field evolution results in the dark matter abundance as a simple function of the fundamental parameters of the axion. The misalignment mechanism with friction broadens the viable parameter space of axion-like particles, and even the QCD axion to the large decay constant regime. We investigate the relevant parameter regions and phenomenological constraints on the axion parameters. Moreover, we numerically study how the density perturbations grow with friction. We discuss the implications of the density perturbations in the pre- and post- inflationary scenarios.