Stochastic Ultra Slow Roll Inflation

Abstract

We study the ultra slow roll model in the context of stochastic inflation. Using stochastic $\delta N$ formalism, we calculate the mean number of $e$-folds, the power spectrum, the bispectrum and the stochastic corrections into these observables. We reproduce correctly the known leading classical contributions to these cosmological observables while we show that the fractional corrections to cosmological observables induced from stochastic dynamics are at the order of power spectrum. In addition, we consider a hypothetical setup containing two absorbing barriers on both sides of the field configuration and calculate the probability of first boundary crossing associated with the classical motion and quantum jumps. This analysis includes the limit of Brownian motion of the quantum fluctuations of a test scalar field in a dS spacetime.