Inflation with Massive Vector Fields
  We investigate the coupling between the inflaton and massive vector fields.
All renormalizable couplings with shift symmetry of the inflaton are
considered. The massive vector can be decomposed into a scalar mode and a
divergence-free vector mode. We show that the former naturally interacts with
the inflaton and the latter decouples at tree level. The model in general
predicts $f_{NL}^\mathrm{equil} = \mathcal{O}(1)$, while in some regions of the
parameter space large non-Gaussianity can arise.
