Speaker: Subodh Patil
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 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 illustrative 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 that the influence of heavy fields on the adiabatic mode cannot be neglected 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 primordial spectra that correlate over different n-point functions. We comment on the prospects of observing such correlations in future LSS and 21 cm observations, the observation of which would provide a model independent confirmation of the nature of the inflaton as an effective, weakly coupled single field that gave rise to the observed structure.