On Squeezed Limits in Single-Field Inflation - Part I
  The n-point correlation functions in single-field inflation obey a set of
consistency conditions in the exact squeezed limit which are not present in
multi-field models, and thus are powerful tools to distinguish between the two.
However, these consistency conditions may be violated for a finite range of
scales in single-field models, for example by departures from the Bunch-Davies
state. These it excited states may be the consequence of interactions during
inflation, or may be a remnant of the era that preceded inflation. In this
paper we analyze the bispectrum, and show that in the regime of theoretical
control the resulting signal in the squeezed limit remains undetectably small
in all known models which continuously excite the state. We also show that the
signal remains undetectably small if the initial state is related to the
Bunch-Davies state by a Bogoliubov transformation and the energy density in the
state is small enough so that the usual slow-roll conditions are obeyed.
Bogoliubov states that lead to violations of the slow-roll conditions, as well
as more general excited states, require more careful treatment and will be
discussed in a separate publication.
