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Lookup NU author(s): Dr Gerasimos RigopoulosORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
We examine the classical and quantum evolution of inflationary cosmological perturbations from quantum initial conditions, using the on-shell and off-shell contributions to correlators to investigate the signatures of interactions. In particular, we calculate the Keldysh contributions to the leading order bispectrum from past infinity, showing that the squeezed limit is dominated by the on-shell evolution. By truncating the time integrals in the analytic expressions for contributions to the bispectrum, we define a `quantum interactivity' and quantitatively identify scales and times for which it is sufficient to only assume classical evolution, given a fixed precision. In contrast to typical perceptions inspired by free two-point functions, we show that common non-linear contributions to inflationary perturbations can be well-described by classical evolution even prior to horizon crossing. The insights gained here can pave the way for quantitative criteria for justifying the validity of numerically simulating the generation and evolution of quantum fluctuations in inflation. In particular, we comment on the validity of using stochastic inflation to reproduce known in-in perturbative results. An extensive appendix provides a review of the Keldysh formulation of the in-in formalism with the initial state set at a finite, as opposed to infinite past, emphasizing the importance of considering temporal boundary terms and the initial state for correctly obtaining the propagators. We also show how stochastic dynamics can emerge as a sufficiently accurate approximation to the full quantum evolution. This becomes particularly transparent in the Keldysh description.
Author(s): Launay YL, Rigopoulos GI, Shellard EPS
Publication type: Article
Publication status: Published
Journal: Journal of Cosmology and Astroparticle Physics
Year: 2025
Volume: 2025
Issue: 05
Print publication date: 23/05/2025
Online publication date: 23/05/2025
Acceptance date: 31/03/2025
Date deposited: 27/05/2025
ISSN (electronic): 1475-7516
Publisher: IOP
URL: https://doi.org/10.1088/1475-7516/2025/05/071
DOI: 10.1088/1475-7516/2025/05/071
Notes:
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