TY - JOUR

T1 - Stochastic inflation with an extremely large number of e-folds

AU - Kitajima, Naoya

AU - Tada, Yuichiro

AU - Takahashi, Fuminobu

N1 - Funding Information:
F.T. thanks Wen Yin for discussion on the eternal inflation. This work is supported by JSPS KAKENHI Grant Numbers JP15H05889 (F.T.), JP15K21733 (F.T.), JP17H02875 (F.T.), JP17H02878 (F.T.), JP18J01992 (Y.T.), JP19K14707 (Y.T.), JP18H01243 (N.K.), JP19K14708 (N.K.), JP19H01894 (N.K.), and by World Premier International Research Center Initiative (WPI Initiative), MEXT , Japan.
Publisher Copyright:
© 2019 The Authors

PY - 2020/1/10

Y1 - 2020/1/10

N2 - 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.

AB - 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.

KW - Axion

KW - Eternal inflation

KW - IPMU19-0102

KW - Stochastic inflation

KW - TU-1090

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U2 - 10.1016/j.physletb.2019.135097

DO - 10.1016/j.physletb.2019.135097

M3 - Article

AN - SCOPUS:85075985121

SN - 0370-2693

VL - 800

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

M1 - 135097

ER -