Fast computation of first-order feature-bispectrum corrections

Abstract

Features in the inflaton potential that are traversed in much less than an $e$-fold of the expansion can produce observably large non-Gaussianity. In these models first-order corrections to the curvature mode function evolution induce effects at second order in the slow-roll parameters that are generically greater than $\ensuremath{\sim}10%$ and can reach order unity for order unity power spectrum features. From a complete first-order expression in generalized slow roll, we devise a computationally efficient method that is as simple to evaluate as the leading-order one and implements consistency relations in a controlled fashion. This expression matches direct numerical computation for step potential models of the dominant bispectrum configurations to better than 1% when features are small and 10% when features are order unity.