Title: Heavy fields, Decoupling and the Effective theory of Inflation
Abstract: Heavy fields can play a surprisingly large role in the dynamics of the
adiabatic mode during inflation, consistent with the validity of an
effective single field description. In this talk, we will review recent
developments in the effective theory (EFT) of inflation, offer a brief
tour of the two main approaches, and along the way point out various
subtleties of how decoupling is operative on time dependent backgrounds.
In the context of a two field system (with one field much more massive
than the other) we will derive the EFT for the light degrees of freedom
and show how heavy fields can be excited whenever the background
trajectory `bends' sufficiently in field space. This occurs even when
the mass of the heavy field is several orders of magnitude larger than
the Hubble scale during inflation, entirely consistent with slow roll
and the decoupling of the true high energy modes of the system. At the
level of the EFT this is due to certain operators briefly transmuting
into relevance, the result of which imprints features in the power
spectrum and can generate a scale dependent non-gaussianity that peaks
for equilateral shapes. We comment on the prospects seeing any such
imprints of higher dimensional operators in future CMB and LSS
observations.