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In search of an observational quantum signature of the primordial perturbations in slow-roll and ultraslow-roll inflation

de Putter, Roland and Doré, Olivier (2020) In search of an observational quantum signature of the primordial perturbations in slow-roll and ultraslow-roll inflation. Physical Review D, 101 (4). Art. No. 043511. ISSN 2470-0010.

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In the standard inflationary paradigm, cosmological density perturbations are generated as quantum fluctuations in the early Universe, but then undergo a quantum-to-classical transition. A key role in this transition is played by squeezing of the quantum state, which is a result of the strong suppression of the decaying mode component of the perturbations. Motivated by ever improving measurements of the cosmological perturbations, we ask whether there are scenarios where this decaying mode is nevertheless still observable in the late Universe, ideally leading to a “smoking gun” signature of the quantum nature of the perturbations. We address this question by evolving the quantum state of the perturbations from inflation into the postinflationary Universe. After recovering the standard result that in slow-roll (SR) inflation the decaying mode is indeed hopelessly suppressed by the time the perturbations are observed (by ∼115 orders of magnitude), we turn to ultraslow-roll (USR) inflation, a scenario in which the usual decaying mode actually grows on superhorizon scales. Despite this drastic difference in the behavior of the mode functions, we find also in USR that the late-Universe decaying mode amplitude is dramatically suppressed, in fact by the same ∼115 orders of magnitude. We finally explain that this large suppression is a general result that holds beyond the SR and USR scenarios considered and follows from a modified version of Heisenberg’s uncertainty principle and the observed amplitude of the primordial power spectrum. The classical behavior of the perturbations is thus closely related to the classical behavior of macroscopic objects drawing an analogy with the position of a massive particle, the curvature perturbations today have an enormous effective mass of order m²_(pl)/H²₀∼10¹²⁰, making them highly classical.

Item Type:Article
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URLURL TypeDescription Paper
Doré, Olivier0000-0002-5009-7563
Alternate Title:In search of an observational quantum signature of the primordial perturbations in slow-roll and ultra slow-roll inflation
Additional Information:© 2020 American Physical Society. Received 28 May 2019; accepted 20 December 2019; published 11 February 2020. We would like to thank Chen He Heinrich, Tomislav Prokopec, Jérôme Martin, Enrico Pajer, Daniel Baumann, Daniel Green, and Jérôme Gleyzes for helpful discussions and gratefully acknowledge support by the Heising-Simons Foundation. Part of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
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Heising-Simons FoundationUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20190930-154022846
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98973
Deposited By: Tony Diaz
Deposited On:30 Sep 2019 22:54
Last Modified:28 Sep 2020 16:14

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