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Does inflation squeeze cosmological perturbations?

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arxiv 2203.07066 v1 pith:SSIWFEQP submitted 2022-03-14 gr-qc astro-ph.COhep-thquant-ph

classification gr-qcastro-ph.COhep-thquant-ph
keywords perturbationsquestionarguecosmologicalinflationmodesquantumused
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abstract

There seems to exist agreement about the fact that inflation squeezes the quantum state of cosmological perturbations and entangles modes with wavenumbers $\vec k$ and $-\vec k$. Paradoxically, this result has been used to justify both the classicality as well as the quantumness of the primordial perturbations at the end of inflation. We reexamine this question and point out that the definition of two-mode squeezing of the modes $\vec k$ and $-\vec k$ used in previous work rests on choices that are only justified for systems with time-independent Hamiltonians and finitely many degrees of freedom. We argue that for quantum fields propagating on generic time-dependent Friedmann-Lema\^itre-Robertson-Walker backgrounds, the notion of squeezed states is subject to ambiguities, which go hand in hand with the ambiguity in the definition of particles. In other words, we argue that the question "does the cosmic expansion squeeze and entangle modes with wavenumbers $\vec k$ and $-\vec k$?" contains the same ambiguity as the question "does the cosmic expansion create particles?". When additional symmetries are present, like in the (quasi) de Sitter-like spacetimes used in inflationary models, one can resolve the ambiguities, and we find that the answer to the question in the title turns out to be in the negative. We further argue that this fact does not make the state of cosmological perturbations any less quantum, at least when deviations from Gaussianity can be neglected.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. When inflationary perturbations refuse to classicalise: the role of non-Gaussianity in Wigner negativity

    gr-qc 2026-01 conditional novelty 6.0 of 10

    In ultra-slow-roll inflation, the Wigner function of the inflationary Goldstone field becomes negative and its negativity grows with the scale factor squared, so the perturbations do not automatically become classical.

  2. $\delta n$ formalism: A new formulation for the probability density of the curvature perturbation

    astro-ph.CO 2025-05 conditional novelty 5.0 of 10

    A reformulation of the δN formalism that counts e-folds forward and exploits the superhorizon correlation between field and velocity to express the curvature perturbation PDF as a one-dimensional change of variables.

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