On the Scale of New Physics in Inflation
  Effective field theory is a powerful organizing principle that allows to
describe physics below a certain scale model-independently. Above that energy
scale, identified with the cutoff, the EFT description breaks down and new
physics is expected to appear, as confirmed in many familiar examples in
quantum field theory. In this work, we examine the validity of effective field
theory methods applied to inflation. We address the issue of whether
Planck-suppressed non-renormalizable interactions are suppressed enough to be
safely neglected when computing inflationary predictions. We focus on
non-derivative non-renormalizable operators and estimate the cutoff that should
suppress them using two independent approaches: (i) the usual unitarity and
perturbativity argument, (ii) by computing the UV-divergent part of the
inflaton entropy, known to scale as the square of the UV-cutoff. We find that
in the absence of gravity (decoupling limit) the cutoff appears to depends
linearly on the total inflaton excursion. On the other hand, once gravity is
restored, the cutoff is brought back to the Planck scale. These results suggest
that inflationary scenarios with super-Planckian excursion are not natural from
the EFT viewpoint.
