Axions, Time Varying CP Violation, and Baryogenesis

Abstract

We derive two features of axion cosmology that may have cosmological implications, whether or not axions are dark matter: For the full range of allowed axion masses, the evolution of a cosmic axion background allows large CP violation until temperatures as low as $\sim$ 2 GeV, and once the axion field begins to oscillate, the cosmological axion field's relaxation to its ground state can briefly provide a new departure from thermal equilibrium, via time-varying CP violation. During both of these periods, the Strong CP violating parameter $\bar{\theta }$ can be as large as O(1).

Comments: 3 pages, submitted to Phys. Rev.D, also references corrected