Mixed axion/neutralino dark matter in the SUSY DFSZ axion model

We examine mixed axion/neutralino cold dark matter production in the SUSY DFSZ axion model where an axion superfield couples to Higgs superfields. We calculate a wide array of axino and saxion decay modes along with their decay temperatures, and thermal and non-thermal production rates. For a SUSY benchmark model with a standard underabundance (SUA) of Higgsino-like dark matter (DM), we find for the PQ scale fa10¹² GeV that the DM abundance is mainly comprised of axions as the saxion/axino decay occurs before the standard neutralino freeze-out and thus its abundance remains suppressed. For 10 ¹²fa10¹⁴ GeV, the saxion/axino decays occur after neutralino freeze-out so that the neutralino abundance is enhanced by the production via decay and subsequent re-annihilation. For fa10¹⁴ GeV, both neutralino dark matter and dark radiation are typically overproduced. For judicious parameter choices, these can be suppressed and the combined neutralino/axion abundance brought into accord with measured values. A SUSY benchmark model with a standard overabundance (SOA) of bino DM is also examined and typically remains excluded due at least to too great a neutralino DM abundance for fa10¹⁵ GeV. For fa10¹⁵ GeV and lower saxion masses, large entropy production from saxion decay can dilute all relics and the SOA model can be allowed by all constraints.