Dilution of axion dark radiation by thermal inflation
  Axions in the Peccei-Quinn (PQ) mechanism provide a promising solution to the
strong CP problem in the standard model of particle physics. Coherently
generated PQ scalar fields could dominate the energy density in the early
Universe and decay into relativistic axions, which would conflict with the
current dark radiation constraints. We study the possibility that a thermal
inflation driven by a $U(1)$ gauged Higgs field dilutes such axions. A
well-motivated extra gauged $U(1)$ would be the local $B-L$ symmetry. We also
discuss the implication for the case of $U(1)_{B-L}$ and an available
baryogenesis mechanism in such cosmology.
