Dynamical axion misalignment with small instantons

Understand

We present a new mechanism to relax the initial misalignment angle of the QCD axion and raise the cosmological bound on the axion decay constant.

• The QCD axion receives a contribution from small UV instantons during inflation, which raises its mass to the inflationary Hubble scale.
• This makes the axion start rolling down its potential early on.
• In the scenario, the standard model Yukawa couplings of quarks are dynamical, being of order one during the inflationary era and reducing to their standard model values once it ends.