Non-Gaussianities and Curvature Perturbations from Hybrid Inflation

Understand

For the original hybrid inflation as well as the supersymmetric F-term and D-term hybrid models, we calculate the level of non-gaussianities and the power spectrum of curvature perturbations generated during the waterfall, taking into account the contribution of entropic modes.

• We focus on the regime of mild waterfall, in which inflation continues for more than about 60 e-folds N during the waterfall.
• We find that the associated f_nl parameter goes typically from f_nl \simeq -1 / N_exit in the regime with N >> 60, where N_exit is the number of e-folds between the time of Hubble exit of a pivot scale and the end of inflation, down to f_nl ~-0.3 when N \gtrsim 60, i.e.
• much smaller in magnitude than the current bound from Planck.