Nima began by giving us overviews of inflation and of the effective field approach (EFT). EFTs are used either when one wants to simplify a known true theory for a particular energy range, or when the true theory is unknown but the underlying symmetries are.
Nima explained that in the case of multi-field inflation the symmetry in question is general covariance and that the most general Langrangian consistent with inflation has a great many terms. This is turn means many simplifications are needed in order to extract useful physics.
A similar EFT analysis for inflation has been carried out for single field inflation by Weinberg, and Nima focussed on the new interactions that are unique to multi-field models. These interactions can give rise to non-gaussianities in the primordial fluctuations, which may be detected with current and future CMB and large scale structure experiments.
After discussing the regimes for which the EFT approach was valid Nima moved on to the specific case of a two field model that he had studied. Here, Nima explained that the model predicts relationships between different shapes of non-gaussianity, proving a potentially valuable probe of multi-field inflation.
The talk finished with Nima’s conclusions, highlighting the possible non-gaussianity signals and contrasting his approach to multifield inflation EFT with others.