Stochastic inflation with an extremely large number of e-folds

• Main Authors: Naoya Kitajima, Yuichiro Tada, Fuminobu Takahashi
• Format: Article
• Language: English
• Published: Elsevier 2020-01-01
• Series: Physics Letters B
• Online Access: http://www.sciencedirect.com/science/article/pii/S0370269319308196

We propose a class of single-field, slow-roll inflation models in which a typical number of e-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 e-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 e-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 e-folds can be as large as 101010, which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution. Keywords: Stochastic inflation, Eternal inflation, Axion, TU-1090, IPMU19-0102