Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 5, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1475-7516/2018/05/012
Keywords
inflation; non-gaussianity; cosmological perturbation theory
Funding
- Chinese National Youth Thousand Talents Program
- NSFC [11653002, 11722327, 11421303]
- CAST Young Elite Scientists Sponsorship Program [2016QNRC001]
- Fundamental Research Funds for the Central Universities
- NSF [PHY-1417421]
- U.S. Department of Energy [de-sc0012567]
- MEXT KAKENHI [15H05888, 15K21733]
- Netherlands Organization for Scientific Research (NWO)
- Department of Physics at McGill University
- Fund for Fostering Talents in Basic Science of the NSFC [J1310021]
- Direct For Mathematical & Physical Scien
- Division Of Physics [1650217] Funding Source: National Science Foundation
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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.
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