Fast Computation of First-Order Feature-Bispectrum Corrections

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 ~ 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.