Revisiting non-Gaussianity from non-attractor inflation models
Author(s)Cai, Yi-Fu; Chen, Xingang; Namjoo, Mohammad Hossein; Sasaki, Misao; Wang, Dong-Gang; Wang, Ziwei; ... Show more Show less
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Non-attractor inflation is known as the only single field inflationary scenario that can violate non-Gaussianity consistency relation with the Bunch-Davies vacuum state and generate large local non-Gaussianity. However, it is also known that the non-attractor inflation by itself is incomplete and should be followed by a phase of slow-roll attractor. Moreover, there is a transition process between these two phases. In the past literature, this transition was approximated as instant and the evolution of non-Gaussianity in this phase was not fully studied. In this paper, we follow the detailed evolution of the non-Gaussianity through the transition phase into the slow-roll attractor phase, considering different types of transition. We find that the transition process has important effect on the size of the local non-Gaussianity. We first compute the net contribution of the non-Gaussianities at the end of inflation in canonical non-attractor models. If the curvature perturbations keep evolving during the transition - such as in the case of smooth transition or some sharp transition scenarios - the O(1) local non-Gaussianity generated in the non-attractor phase can be completely erased by the subsequent evolution, although the consistency relation remains violated. In extremal cases of sharp transition where the super-horizon modes freeze immediately right after the end of the non-attractor phase, the original non-attractor result can be recovered. We also study models with non-canonical kinetic terms, and find that the transition can typically contribute a suppression factor in the squeezed bispectrum, but the final local non-Gaussianity can still be made parametrically large.
DepartmentMassachusetts Institute of Technology. Department of Physics
Journal of Cosmology and Astroparticle Physics
Cai, Yi-Fu, Xingang Chen, Mohammad Hossein Namjoo, Misao Sasaki, Dong-Gang Wang, and Ziwei Wang. “Revisiting Non-Gaussianity from Non-Attractor Inflation Models.” Journal of Cosmology and Astroparticle Physics 2018, no. 05 (May 3, 2018): 012–012. © 2018 IOP Publishing Ltd and Sissa Medialab
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