  The implementation of a Planck-scale high frequency and short wavelength
cutoff in quantum theories on expanding backgrounds may have potentially
nontrivial implications, such as the breaking of local Lorentz invariance and
the existence of a yet unknown mechanism for the creation of vacuum modes. In
scenarios where inflation begins close to the cutoff scale, these effects could
have observable consequences as trans-Planckian modes are redshifted to
cosmological scales. In close analogy with similar studies of Hawking
radiation, a simple theory of a minimally coupled scalar field in de Sitter
space is studied, with a high frequency cutoff imposed by a nonlinear
dispersion relation. Under certain conditions the model predicts deviations
from the standard inflationary scenario. We also comment on the difficulties in
generalizing fluid models of Hawking radiation to cosmological space-times.
