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Recent studies of inflation with multiple scalar fields have highlighted theimportance of non-canonical kinetic terms in novel types of inflationarysolutions. This motivates a thorough analysis of non-Gaussianities in thiscontext, which we revisit here by studying the primordial bispectrum in ageneral two-field model. Our main result is the complete cubic action forinflationary fluctuations written in comoving gauge, i.e. in terms of thecurvature perturbation and the entropic mode. Although full expressions for thecubic action have already been derived in terms of fields fluctuations in theflat gauge, their applicability is mostly restricted to numerical evaluations.Our form of the action is instead amenable to several analyticalapproximations, as our calculation in terms of the directly observable quantitymakes manifest the scaling of every operator in terms of the slow-rollparameters, what is essentially a generalization of Maldacena's single-fieldresult to non-canonical two-field models. As an important application we derivethe single-field effective field theory that is valid when the entropic mode isheavy and may be integrated out, underlining the observable effects that derivefrom a curved field space.

Revisiting non-Gaussianity in multifield inflation with curved field space