Quantum states of the bouncing universe

TL;DR

This paper investigates quantum dynamics in a bouncing universe model, analyzing various quantum states and their semiclassical limits, and explores decoherence and interpretative aspects within loop quantum cosmology.

Contribution

It introduces a unitary transformation simplifying the quantum description and examines properties of different quantum states in a bouncing cosmological model.

Findings

Quantum states exhibit semiclassical behavior under certain parameters.

Decoherence of superposed universes is characterized.

Negative regions of Wigner functions reveal quantum features.

Abstract

In this paper we study quantum dynamics of the bouncing cosmological model. We focus on the model of the flat Friedman-Robertson-Walker universe with a free scalar field. The bouncing behavior, which replaces classical singularity, appears due to the modification of general relativity along the methods of loop quantum cosmology. We show that there exist a unitary transformation that enables to describe the system as a free particle with Hamiltonian equal to canonical momentum. We examine properties of the various quantum states of the Universe: boxcar state, standard coherent state, and soliton-like state, as well as Schr{\"o}dinger's cat states constructed from these states. Characteristics of the states such as quantum moments and Wigner functions are investigated. We show that each of these states have, for some range of parameters, a proper semiclassical limit fulfilling the correspondence principle. Decoherence of the superposition of two universes is described and possible interpretations in terms of triad orientation and Belinsky-Khalatnikov-Lifshitz conjecture are given. Some interesting features regarding the area of the negative part of the Wigner function have emerged.