QCD axions and axionlike particles in a two-inflation scenario

Understand

We investigate the phenomenology of QCD axions and axionlike particles in a scenario with two eras of inflation.

• In particular, we describe the possible solutions for the QCD axion field equation after the second inflation and reheating.
• We calculate the dilution numerically for QCD axions and give an analytic approximation for axionlike particles.
• While it has been realised before that such a scenario can dilute the axion energy density and open up the parameter space for the axion decay constant $f_A$, we find that even a small increase in the relative QCD axion energy density is possible.