On the emergence of a classical isotropic universe from a quantum f(R) Bianchi cosmology in the Jordan frame

Angelis, Mariaveronica De; Montani, Giovanni

doi:10.1140/epjc/s10052-023-11454-6

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Eur. Phys. J. C

2023

DOI: 10.1140/epjc/s10052-023-11454-6

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On the emergence of a classical isotropic universe from a quantum f(R) Bianchi cosmology in the Jordan frame

Mariaveronica De Angelis

Giovanni Montani

Abstract: We demonstrate a spontaneous tendency of quantum wave packets to become quasi-classical, providing a classical limit for the Universe dynamics. However, this limit is not maintained in the future (after a critical value of the relational time) and a spreading process is turned on. We show that the onset of an inflationary scenario is not able to make this localization stable of the wave packets for the Bianchi I model. Instead, when we implement a perturbative inflationary scenario for the isotropic Universe a… Show more

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WKB Approaches to Restore Time in Quantum Cosmology: Predictions and Shortcomings

2022

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In this review, we analyse different aspects concerning the possibility to separate a gravity-matter system into a part which lives close to a quasi-classical state and a “small” quantum subset. The considered approaches are all relying on a WKB expansion of the dynamics by an order parameter and the natural arena consists of the Bianchi universe minisuperspace. We first discuss how, limiting the WKB expansion to the first order of approximation, it is possible to recover for the quantum subsystem a Schrödinger equation, as written on the classical gravitational background. Then, after having tested the validity of the approximation scheme for the Bianchi I model, we give some applications for the quantum subsystem in the so-called “corner” configuration of the Bianchi IX model. We individualize the quantum variable in the small one of the two anisotropy degrees of freedom. The most surprising result is the possibility to obtain a non-singular Bianchi IX cosmology when the scenario is extrapolated backwards in time. In this respect, we provide some basic hints on the extension of this result to the generic cosmological solution. In the last part of the review, we consider the same scheme to the next order of approximation identifying the quantum subset as made of matter variables only. This way, we are considering the very fundamental problem of non-unitary morphology of the quantum gravity corrections to quantum field theory discussing some proposed reformulations. Instead of constructing the time dependence via that one of the classical gravitational variables on the label time as in previous works, we analyse a recent proposal to construct time by fixing a reference frame. This scheme can be reached both introducing the so-called “kinematical action”, as well as by the well-known Kuchar–Torre formulation. In both cases, the Schrödinger equation, amended for quantum gravity corrections, has the same morphology and we provide a cosmological implementation of the model, to elucidate its possible predictions.

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WKB Approaches to Restore Time in Quantum Cosmology: Predictions and Shortcomings

2022

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On the emergence of a classical isotropic universe from a quantum f(R) Bianchi cosmology in the Jordan frame

Cited by 1 publication

References 50 publications

WKB Approaches to Restore Time in Quantum Cosmology: Predictions and Shortcomings

WKB Approaches to Restore Time in Quantum Cosmology: Predictions and Shortcomings

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