Model-independent predictions for n and dn/d lnk from a broad class of inflationary models

Abstract

We explore a well-motivated class of inflationary models from the particle physics point of view: those with a flat tree-level potential, where the radiative corrections cause the slow rolling of the inflaton and the running of the spectral index n. This includes typical SUSY inflation models (e.g. D-hybrid inflation). In the small-coupling regime the predictions for the size and running of n are remarkably neat and model independent, e.g. −dn/d ln k = (n − 1)2 ≪ 1. The fit to WMAP data gives the number of e-folds, Ne, as an output: Ne = 26+30−8, which is very encouraging. On the other hand, to account for the WMAP preliminary indication of a running n crossing n = 1, we find it extremely natural to incorporate non-renormalizable operators (only the dominant one is relevant), which automatically increase the running as demanded. The analysis is still very model independent and predicts a rapidly changing n at the initial scales, which then gets stabilized below n = 1.