paper

Stochastic inflation with an extremely large number of -folds

arXiv:1908.08694 · doi:10.1016/j.physletb.2019.135097

Abstract

We propose a class of single-field, slow-roll inflation models in which a typical number of -folds can be extremely large. The key point is to introduce a very shallow local minimum near the top of the potential in a hilltop inflation model. In particular, a typical number of -folds is enhanced if classical behavior dominates around the local minimum such that the inflaton probability distribution is drifted to the local minimum as a whole. After the inflaton escapes from the local minimum due to the stochastic dynamics, the ordinary slow-roll inflation follows and it can generate the primordial density perturbation consistent with observation. Interestingly, our scenario inherits the advantages of the old and new inflation: the typical -folds can be extremely large as in the old inflation, and slow-roll inflation naturally follows after the stochastic regime as in the new inflation. In our numerical example, the typical number of -folds can be as large as , which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.

6 pages, 3 figures; v2: published version, Fig. 1 added, Figs. 2 & 3 revised

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