Stochastic inflation with an extremely large number of e-folds

Abstract

We propose a class of single-field, slow-roll inflation models in which a typical number of efolds 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 10 10 8 , which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.

Hidden Photon and Axion Dark Matter from Symmetry Breaking

“…Refs. [137,138]) and later s tunnels through the potential barrier. After the tunneling, still the curvature of the potential may be suppressed enough and then the quartic hilltop inflation happens there [139][140][141] if the quartic coupling is negative.…”

QCD axion window and false vacuum Higgs inflation

“…ref. [97]). As we have seen before, the Higgs acquires a negative mass from the potential like (5.7) during inflation where ϕ 0.…”

“…It is possible to make the typical e-folds extremely large (e.g. N ∼ 10 10 10 ) in a stochastic inflation model where the potential has a shallow local minimum around the hilltop[97].…”

Hidden photon and axion dark matter from symmetry breaking

“…refs. [148,149]) and later s tunnels through the potential barrier. After the tunneling, still the curvature of the potential may be suppressed enough and then the quartic hilltop inflation happens there [150][151][152] if the quartic coupling is negative.…”