Recent Advances in Quantum Cosmology

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Cosmology".

Deadline for manuscript submissions: closed (29 February 2024) | Viewed by 4494

Special Issue Editor

1. ENEA, Fusion and Nuclear Safety Department, C.R. Frascati, Via E. Fermi 45, 00044 Frascati, Italy
2. Physics Department, “Sapienza” University of Rome, P.le Aldo Moro 5, 00185 Roma, Italy
Interests: primordial cosmology; quantum gravity; modified theories of gravity; plasma astrophysics; cosmological plasmas; turbulent transport in plasmas

Special Issue Information

Dear Colleagues,

The dynamics of the quantum universe is an excellent arena to test the predictivity of different proposals for a quantum theory of gravity, and in some cases, the mini-superspace formulation is rich with physical insight.

In the last two decades, quantum cosmology has been characterized by a new impulse, mainly due to the formulation of Big-Bounce dynamics in Loop Quantum Cosmology. Further, other formulations based on a covariant description of the gravitational field dynamics have been successful in offering physical intuitions on the emergence of a classical Universe from the Planckian era.

Despite this improvement of our understanding about the notion and the meaning of a quantum universe, many relevant open questions remain in the field and call attention for further discussion and investigation. For this reason, the goal of this issue is to put together material coming from different approaches and try to find those common features which could constitute a valuable horizon for future studies.

This Special Issue aims at focusing attention on the most recent and promising developments in quantum cosmology, both in the canonical formulation, as well as in covariant approaches (e.g., path integral or covariant loop quantum gravity studies). Three main aspects are considered: (i) proposals for suitable clocks in quantum cosmologies; (ii) the implementation of fundamental symmetries in the mini-superspace; (iii) the emergence of Big-Bounce dynamics. Implications on universe quantum dynamics, coming from extended theories of gravity, are also considered. We invite the submission of original papers in the form of regular articles or short letters, but also review articles dedicated to selected topics in quantum cosmology.

Prof. Dr. Giovanni Montani
Guest Editor

Manuscript Submission Information

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Keywords

  • Big-Bounce scenarios
  • time in quantum cosmology
  • symmetries of the quantum universe
  • canonical quantum cosmology
  • covariant approaches to quantum cosmology
  • quantum cosmology from extended gravity

Published Papers (4 papers)

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Research

31 pages, 1248 KiB  
Article
A Loop Quantum-Corrected Family of Chiral Cosmology Models
Universe 2024, 10(2), 88; https://doi.org/10.3390/universe10020088 - 12 Feb 2024
Viewed by 484
Abstract
We construct and examine a holonomy-corrected chiral fields model of cosmological relevance. Specifically, we holonomize the Hamiltonian corresponding to a quintom field scenario with additional kinetic interaction (governed by the constant chiral metric, mab) on a flat FLRW background and [...] Read more.
We construct and examine a holonomy-corrected chiral fields model of cosmological relevance. Specifically, we holonomize the Hamiltonian corresponding to a quintom field scenario with additional kinetic interaction (governed by the constant chiral metric, mab) on a flat FLRW background and contrast the resulting model with the corresponding purely classical system. In particular, it is shown that the single LQC bouncing stage is ensured to be realized, provided the full chiral kinetic energy function does not change sign during evolution. (As preparation, a particularly simple k-essence field is examined within the effective LQC scheme; some exact solutions are obtained in the process.) Additionally, under the said assumption, it is established that the landmark bouncing mechanism of standard (effective) LQC is still guaranteed to be featured even when taking any finite number of fields ϕ1,ϕm and mab to be dependent on such fields (the particular zero-potential case corresponding to a family of simple purely kinetic k-essence multi-field cosmology models). Full article
(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
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15 pages, 463 KiB  
Article
Scalar Product for a Version of Minisuperspace Model with Grassmann Variables
Universe 2023, 9(12), 508; https://doi.org/10.3390/universe9120508 - 07 Dec 2023
Viewed by 942
Abstract
Grassmann variables are used to formally transform a system with constraints into an unconstrained system. As a result, the Schrödinger equation arises instead of the Wheeler–DeWitt one. The Schrödinger equation describes a system’s evolution, but a definition of the scalar product is needed [...] Read more.
Grassmann variables are used to formally transform a system with constraints into an unconstrained system. As a result, the Schrödinger equation arises instead of the Wheeler–DeWitt one. The Schrödinger equation describes a system’s evolution, but a definition of the scalar product is needed to calculate the mean values of the operators. We suggest an explicit formula for the scalar product related to the Klein–Gordon scalar product. The calculation of the mean values is compared with an etalon method in which a redundant degree of freedom is excluded. Nevertheless, we note that a complete correspondence with the etalon picture is not found. Apparently, the picture with Grassmann variables requires a further understanding of the underlying Hilbert space. Full article
(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
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23 pages, 414 KiB  
Article
Study of the Inflationary Spectrum in the Presence of Quantum Gravity Corrections
Universe 2023, 9(4), 169; https://doi.org/10.3390/universe9040169 - 30 Mar 2023
Cited by 2 | Viewed by 875
Abstract
After a brief review of the different approaches to predicting the possible quantum gravity corrections to quantum field theory, we discuss in some detail the formulation based on a Gaussian reference frame fixing. Then, we utilize this scenario in the determination of the [...] Read more.
After a brief review of the different approaches to predicting the possible quantum gravity corrections to quantum field theory, we discuss in some detail the formulation based on a Gaussian reference frame fixing. Then, we utilize this scenario in the determination of the inflationary spectrum of primordial perturbations. We consider the quantization of an inhomogeneous, free, massless scalar field in a quasi-classical isotropic Universe by developing a WKB expansion of the dynamics of the next order in the Planckian parameter, with respect to the one at which standard QFT emerges. The quantum gravity corrections to the scale-invariant spectrum are discussed in a specific primordial cosmological setting and then in a general minisuperspace formalism, showing that there is no mode-dependent effect, and thus the scale invariant inflationary spectrum is preserved. This result is discussed in connection to the absence of a matter backreaction on the gravitational background in the considered paradigm. Full article
(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
21 pages, 2007 KiB  
Article
The Phase Space Analysis of Interacting K-Essence Dark Energy Models in Loop Quantum Cosmology
Universe 2022, 8(10), 520; https://doi.org/10.3390/universe8100520 - 06 Oct 2022
Viewed by 1432
Abstract
The present work deals with two kinds of k-essence dark energy models within the framework of loop quantum cosmology (LQC). The two kinds of k-essence models originates from two forms of Lagrangians, i.e., [...] Read more.
The present work deals with two kinds of k-essence dark energy models within the framework of loop quantum cosmology (LQC). The two kinds of k-essence models originates from two forms of Lagrangians, i.e., L1=F(X)V(ϕ) and L2=F(X)V(ϕ), where F(X) and V(ϕ) stand for the kinetic term and potential of the scalar field ϕ, respectively. Two models are based on different phase variables settings, and the general form of autonomous dynamical system is deduced for each Lagrangian. Then, the dynamical stabilities of the critical points in each model are analysed in different forms of F(X) and V(ϕ). Model I is a 3-dim system with four stable points, and Model II is a 4-dim system but reduced to a 3-dim system using the symmetry analysis, which has five stable points. Moreover, the corresponding cosmological quantities, such as Ωϕ, wϕ and q, are calculated at each critical point. To compare these with the case of the classical Einstein cosmology (EC), the dynamical evolutionary trajectories in the phase space and evolutionary curves of the cosmological quantities are drawn for both EC and LQC cases, which shows that the loop quantum gravity effects diminish in the late-time universe but are significant in the early time. Further, the effects of interaction Q=αHρm on the evolutions of the universe are discussed. With the loop quantum gravity effects, bouncing universe is achieved in both models for different initial values of ϕ0, ϕ˙0, H0, ρ0 and coupling parameter α, which helps to avoid singularities. However, the interaction has little effect on bounce, although it is important to the stability of some critical points. Full article
(This article belongs to the Special Issue Recent Advances in Quantum Cosmology)
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