Non-Gaussianities in multifield inflation: Superhorizon evolution, adiabaticity, and the fate of fNL

We explore the superhorizon generation of large f(NL) of the local form in two-field inflation. We calculate the two-and three-point observables in a general class of potentials which allow for an analytic treatment using the delta N formalism. Motivated by the conservation of the curvature perturbation outside the horizon in the adiabatic mode and also by the observed adiabaticity of the power spectrum, we follow the evolution of f(NL)(local) until it is driven into the adiabatic solution by passing through a phase of effectively single-field inflation. We find that, although large f(NL)(local) may be generated during inflation, such non-gaussianities are transitory and will be exponentially damped as the cosmological fluctuations approach adiabaticity.