V-mode Polarization in Axion Inflation and Preheating
  We study the production of primordial circular ("V-mode") polarization in
axion inflation coupled to fermions and gauge fields, with special attention
paid to (p)reheating. We construct the power spectrum of $V$, and find a
blue-tilted spectrum with index $n_V=4$. This is independent of the dominant
decay channel of the inflaton (direct fermion vs. direct photon production)
