  Pseudo-scalar inflation coupled with U(1) gauge fields through the
Chern-Simons term has been extensively studied. However, new physics arising
from UV theories may still influence the pseudo-scalar field at low-energy
scales, potentially impacting predictions of inflation. In the realm of
effective field theory (EFT), we investigated axion inflation, where operators
from heavy fields are also present, in addition to the axion and gauge fields.
The integrated out fields have two significant effects: the non-linear
dispersion regime and coupling heavy modes to the Chern-Simons term. The first
effect changes the propagation of the curvature fluctuation, while the second
one results in additional operators that contribute to curvature fluctuation
via inverse decay. We derived the power spectrum and magnitude of equilateral
non-Gaussianity in this low-energy EFT. We found that the second effect could
become significant as the mass of heavy fields approaches Hubble scale.
