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Symmetry
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Cosmology and Quantum Vacuum
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Cosmology and Quantum Vacuum

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (30 June 2019) | Viewed by 18157

Special Issue Editor

Prof. Dr. Emilio Elizalde

E-Mail Website
Guest Editor
Consejo Superior de Investigaciones Científicas, Instituto de Ciencias del Espacio (CSIC), Institut d'Estudis Espacials de Catalunya (IEEC/CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
Interests: zeta functions; regularization of infinite sums; spexial functions of mathemtatical physics; vacuum fluctuations; theoretical cosmology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue, “Cosmology and Quantum Vacuum”, will focus on aspects of Theoretical Cosmology which are related with properties of the Quantum Vacuum. The longstanding question: Why we do not see vacuum fluctuations at cosmological scale? is still without an answer that is accepted by everybody. We have indeed detected an acceleration in the cosmic expansion which could be most easily understood as a vacuum effect (dark energy), but the numbers still do not match by many orders of magnitude. Alternative approaches to this problem involve cosmological models which modify the Einstein-Hilbert Lagrangian by adding terms of higher-order in the curvature. Terms of this kind should probably be there, since they appear in most attempts of calculating quantum corrections to General Relativity. At this stage, however, modified gravity models should be confronted both with fundamental theories and with the most recent astronomical data. There is a lot of work to be done to clarify all these questions and this Special Issue will be devoted to them.

Main topics that will be included are:

  • Cosmological models: modified gravities, f(R) and similar theories, non-local models.
  • Quantum vacuum effects and its implications in cosmology.
  • Casimir effect in brane models and other.
  • The cosmological constant problem and quantum vacuum fluctuations.
  • Mathematical physics techniques for quantum vacuum effects.

Additionally, the Special Issue is open to related topics.

Prof. Dr. Emilio Elizalde
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Cosmological models: modified gravities, f(R) and similar theories, non-local models
  • Quantum vacuum effects and its implications in cosmology
  • Casimir effect in brane models and other
  • The cosmological constant problem and quantum vacuum fluctuations
  • Mathematical physics techniques for quantum vacuum effects

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Published Papers (6 papers)

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Research

17 pages, 646 KiB  
Article
Prospects for Searching Thermal Effects, Non-Newtonian Gravity and Axion-Like Particles: Cannex Test of the Quantum Vacuum
by Galina L. Klimchitskaya, Vladimir M. Mostepanenko, René I. P. Sedmik and Hartmut Abele
Symmetry 2019, 11(3), 407; https://doi.org/10.3390/sym11030407 - 20 Mar 2019
Cited by 26 | Viewed by 2696
Abstract
We consider the Cannex (Casimir And Non-Newtonian force EXperiment) test of the quantum vacuum intended for measuring the gradient of the Casimir pressure between two flat parallel plates at large separations and constraining parameters of the chameleon model of dark energy in cosmology. [...] Read more.
We consider the Cannex (Casimir And Non-Newtonian force EXperiment) test of the quantum vacuum intended for measuring the gradient of the Casimir pressure between two flat parallel plates at large separations and constraining parameters of the chameleon model of dark energy in cosmology. A modification of the measurement scheme is proposed that allows simultaneous measurements of both the Casimir pressure and its gradient in one experiment. It is shown that with several improvements the Cannex test will be capable to strengthen the constraints on the parameters of the Yukawa-type interaction by up to an order of magnitude over a wide interaction range. The constraints on the coupling constants between nucleons and axion-like particles, which are considered as the most probable constituents of dark matter, could also be strengthened over a region of axion masses from 1 to 100 meV. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
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16 pages, 423 KiB  
Article
Quantum Fields without Wick Rotation
by Alessio Baldazzi, Roberto Percacci and Vedran Skrinjar
Symmetry 2019, 11(3), 373; https://doi.org/10.3390/sym11030373 - 13 Mar 2019
Cited by 21 | Viewed by 2789
Abstract
We discuss the calculation of one-loop effective actions in Lorentzian spacetimes, based on a very simple application of the method of steepest descent to the integral over the field. We show that for static spacetimes this procedure agrees with the analytic continuation of [...] Read more.
We discuss the calculation of one-loop effective actions in Lorentzian spacetimes, based on a very simple application of the method of steepest descent to the integral over the field. We show that for static spacetimes this procedure agrees with the analytic continuation of Euclidean calculations. We also discuss how to calculate the effective action by integrating a renormalization group equation. We show that the result is independent of arbitrary choices in the definition of the coarse-graining and we see again that the Lorentzian and Euclidean calculations agree. When applied to quantum gravity on static backgrounds, our procedure is equivalent to analytically continuing time and the integral over the conformal factor. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
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26 pages, 371 KiB  
Article
The Gravity of the Classical Klein-Gordon Field
by Piero Chiarelli
Symmetry 2019, 11(3), 322; https://doi.org/10.3390/sym11030322 - 4 Mar 2019
Cited by 6 | Viewed by 2679
Abstract
The work shows that the evolution of the field of the free Klein–Gordon equation (KGE), in the hydrodynamic representation, can be represented by the motion of a mass density ∝ | ψ | 2 subject to the Bohm-type quantum potential, whose equation can [...] Read more.
The work shows that the evolution of the field of the free Klein–Gordon equation (KGE), in the hydrodynamic representation, can be represented by the motion of a mass density ∝ | ψ | 2 subject to the Bohm-type quantum potential, whose equation can be derived by a minimum action principle. Once the quantum hydrodynamic motion equations have been covariantly extended to the curved space-time, the gravity equation (GE), determining the geometry of the space-time, is obtained by minimizing the overall action comprehending the gravitational field. The derived Einstein-like gravity for the KGE field shows an energy-impulse tensor density (EITD) that is a function of the field with the spontaneous emergence of the “cosmological” pressure tensor density (CPTD) that in the classical limit leads to the cosmological constant (CC). The energy-impulse tensor of the theory shows analogies with the modified Brans–Dick gravity with an effective gravity constant G divided by the field squared. Even if the classical cosmological constant is set to zero, the model shows the emergence of a theory-derived quantum CPTD that, in principle, allows to have a stable quantum vacuum (out of the collapsed branched polymer phase) without postulating a non-zero classical CC. In the classical macroscopic limit, the gravity equation of the KGE field leads to the Einstein equation. Moreover, if the boson field of the photon is considered, the EITD correctly leads to its electromagnetic energy-impulse tensor density. The work shows that the cosmological constant can be considered as a second order correction to the Newtonian gravity. The outputs of the theory show that the expectation value of the CPTD is independent by the zero-point vacuum energy density and that it takes contribution only from the space where the mass is localized (and the space-time is curvilinear) while tending to zero as the space-time approaches to the flat vacuum, leading to an overall cosmological effect on the motion of the galaxies that may possibly be compatible with the astronomical observations. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
9 pages, 234 KiB  
Article
Whether an Enormously Large Energy Density of the Quantum Vacuum Is Catastrophic
by Vladimir M. Mostepanenko and Galina L. Klimchitskaya
Symmetry 2019, 11(3), 314; https://doi.org/10.3390/sym11030314 - 2 Mar 2019
Cited by 9 | Viewed by 2407
Abstract
The problem of an enormously large energy density of the quantum vacuum is discussed in connection with the concept of renormalization of physical parameters in quantum field theory. Using the method of dimensional regularization, it is recalled that the normal ordering procedure of [...] Read more.
The problem of an enormously large energy density of the quantum vacuum is discussed in connection with the concept of renormalization of physical parameters in quantum field theory. Using the method of dimensional regularization, it is recalled that the normal ordering procedure of creation and annihilation operators is equivalent to a renormalization of the cosmological constant leading to its zero and nonzero values in Minkowski space-time and in the standard cosmological model, respectively. It is argued that a frequently discussed gravitational effect, resulting from an enormously large energy density described by the nonrenormalized (bare) cosmological constant, might be nonobservable much like some other bare quantities introduced in the formalism of quantum field theory. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
7 pages, 258 KiB  
Article
Massive Spin Zero Fields in Cosmology and the Tail-Free Property
by Valerio Faraoni
Symmetry 2019, 11(1), 36; https://doi.org/10.3390/sym11010036 - 2 Jan 2019
Cited by 4 | Viewed by 2601
Abstract
Fields of spin s ≥ 1 / 2 satisfying wave equations in a curved space obey the Huygens principle under certain conditions clarified by a known theorem. Here, this theorem is generalized to spin zero and applied to an inflaton field in de [...] Read more.
Fields of spin s ≥ 1 / 2 satisfying wave equations in a curved space obey the Huygens principle under certain conditions clarified by a known theorem. Here, this theorem is generalized to spin zero and applied to an inflaton field in de Sitter-like space, showing that tails of scalar radiation are an unavoidable physical feature. Requiring the absence of tails, on the contrary, necessarily implies an unnatural tuning between cosmological constant, scalar field mass, and coupling constant to the curvature. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
46 pages, 483 KiB  
Article
Space-Time Second-Quantization Effects and the Quantum Origin of Cosmological Constant in Covariant Quantum Gravity
by Claudio Cremaschini and Massimo Tessarotto
Symmetry 2018, 10(7), 287; https://doi.org/10.3390/sym10070287 - 16 Jul 2018
Cited by 15 | Viewed by 4129
Abstract
Space-time quantum contributions to the classical Einstein equations of General Relativity are determined. The theoretical background is provided by the non-perturbative theory of manifestly-covariant quantum gravity and the trajectory-based representation of the related quantum wave equation in terms of the Generalized Lagrangian path [...] Read more.
Space-time quantum contributions to the classical Einstein equations of General Relativity are determined. The theoretical background is provided by the non-perturbative theory of manifestly-covariant quantum gravity and the trajectory-based representation of the related quantum wave equation in terms of the Generalized Lagrangian path formalism. To reach the target an extended functional setting is introduced, permitting the treatment of a non-stationary background metric tensor allowed to depend on both space-time coordinates and a suitably-defined invariant proper-time parameter. Based on the Hamiltonian representation of the corresponding quantum hydrodynamic equations occurring in such a context, the quantum-modified Einstein field equations are obtained. As an application, the quantum origin of the cosmological constant is investigated. This is shown to be ascribed to the non-linear Bohm quantum interaction of the gravitational field with itself in vacuum and to depend generally also on the realization of the quantum probability density for the quantum gravitational field tensor. The emerging physical picture predicts a generally non-stationary quantum cosmological constant which originates from fluctuations (i.e., gradients) of vacuum quantum gravitational energy density and is consistent with the existence of quantum massive gravitons. Full article
(This article belongs to the Special Issue Cosmology and Quantum Vacuum)
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