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Symmetry
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Quantum Gravity Condensates
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Quantum Gravity Condensates

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

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 8505

Special Issue Editor

Dr. Daniele Pranzetti

E-Mail Website
Guest Editor
Perimeter Institute for Theoretical Physics, 31 Caroline St N, Waterloo, ON N2L 2Y5, Canada
Interests: quantum gravity; black Hole physics; edge modes; boundary symmetry; holography

Special Issue Information

Dear Colleagues,

The problem of quantum gravity remains unsolved as of today, more than 90 years after the big change in the landscape of theoretical physics in the last century. A further conceptual leap forward is expected to be brought about by the completion of this task, applying the probabilistic quantum description of phenomena to space and time themselves. Generally, in background-independent approaches to quantum gravity, the space–time structure (in both its geometric and topological properties) is dynamically generated from some basic building blocks. The study of the origin and emergence of continuum space–time from these microscopic and fundamentally discrete degrees of freedom represents one of the most relevant paths of research to further test any nonperturbabtive approach.

A new perspective has recently appeared based on the hypothesis that space-time is a sort of condensate of microscopic building blocks and that general relativity emerges as the description of its geometry in a similar way as hydrodynamics and thermodynamics emerge as the macroscopic description of microscopic degrees of freedom. This point of view is gaining support. Results in this direction come from discrete approaches to quantum gravity, e.g., group field theory, where the construction of quantum gravity condensate states allows to describe the effective dynamics of continuum homogeneous quantum geometries; and from results in string theory dualities and in the AdS/CFT correspondence, where an holographic notion of entanglement for quantum field theories with bulk holographic duals has been used to study the emergence of the thermal properties of the dual spacetime. Insights about the possible emergent nature of gravity and geometry are also provided by condensed matter-inspired quantum gravity models and analogue gravity models. All the above results support the idea of general relativity as the hydrodynamics of pre-geometric space–time building blocks and of space–time as a condensate of these elementary constituents. Spacetime and its continuum symmetry would be emergent concepts, valid at macroscopic scales, whose emergence is the result of a collective dynamical process (a phase transition) of the fundamental degrees of freedom.

Moreover, in the last ten years, quantum information theory has constantly gained importance in investigating the fundamental nature of space, time, and matter. The information-theoretic interpretation of the notion of entanglement has provided new tools to investigate the pre-geometric quantum texture of spacetime in several background independent approaches to quantum gravity.

This Special Issue is intended to collect contributions from scientists working on the fields of quantum gravity and information theory, with the aim to enhance and exploit a cross-fertilization of ideas and techniques of crucial importance towards a quantum description of the gravitational field.

Dr. Daniele Pranzetti
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

  • Emergent spacetime
  • Symmetry
  • Group field theory
  • AdS/CFT correspondence
  • Holography and entanglement entropy
  • Black hole thermodynamics
  • Graviton Bose–Einstein condensate
  • Analogue models of gravity
  • Quantum information metric and gravity dual
  • Tensor networks

Published Papers (4 papers)

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Research

22 pages, 1520 KiB  
Article
Wormhole Solutions in Symmetric Teleparallel Gravity with Noncommutative Geometry
by Zinnat Hassan, Ghulam Mustafa and Pradyumn Kumar Sahoo
Symmetry 2021, 13(7), 1260; https://doi.org/10.3390/sym13071260 - 14 Jul 2021
Cited by 36 | Viewed by 2306
Abstract
This article describes the study of wormhole solutions in f(Q) gravity with noncommutative geometry. Here, we considered two different f(Q) models—a linear model f(Q)=αQ and an exponential model [...] Read more.
This article describes the study of wormhole solutions in f(Q) gravity with noncommutative geometry. Here, we considered two different f(Q) models—a linear model f(Q)=αQ and an exponential model f(Q)=Q−α1−e−Q, where Q is the non-metricity and α is the model parameter. In addition, we discussed the existence of wormhole solutions with the help of the Gaussian and Lorentzian distributions of these linear and exponential models. We investigated the feasible solutions and graphically analyzed the different properties of these models by taking appropriate values for the parameter. Moreover, we used the Tolman–Oppenheimer–Volkov (TOV) equation to check the stability of the wormhole solutions that we obtained. Hence, we found that the wormhole solutions obtained with our models are physically capable and stable. Full article
(This article belongs to the Special Issue Quantum Gravity Condensates)
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14 pages, 321 KiB  
Article
Extended Hořava Gravity with Physical Ground-State Wavefunction
by Fu-Wen Shu and Tao Zhang
Symmetry 2021, 13(1), 100; https://doi.org/10.3390/sym13010100 - 8 Jan 2021
Cited by 4 | Viewed by 1597
Abstract
We propose a new extended theory of Hořava gravity based on the following three conditions: (i) power-counting renormalizable, (ii) healthy IR behavior and (iii) a stable vacuum state in a quantized version of the theory. Compared with other extended theories, we stress that [...] Read more.
We propose a new extended theory of Hořava gravity based on the following three conditions: (i) power-counting renormalizable, (ii) healthy IR behavior and (iii) a stable vacuum state in a quantized version of the theory. Compared with other extended theories, we stress that any realistic theory of gravity must have physical ground states when quantization is performed. To fulfill the three conditions, we softly break the detailed balance but keep its basic structure unchanged. It turns out that the new model constructed in this way can avoid the strong coupling problem and remains power-counting renormalizable, moreover, it has a stable vacuum state by an appropriate choice of parameters. Full article
(This article belongs to the Special Issue Quantum Gravity Condensates)
26 pages, 465 KiB  
Article
Composite and Background Fields in Non-Abelian Gauge Models
by Pavel Yu. Moshin and Alexander A. Reshetnyak
Symmetry 2020, 12(12), 1985; https://doi.org/10.3390/sym12121985 - 30 Nov 2020
Cited by 1 | Viewed by 1458
Abstract
A joint introduction of composite and background fields into non-Abelian quantum gauge theories is suggested based on the symmetries of the generating functional of Green’s functions, with the systematic analysis focused on quantum Yang–Mills theories, including the properties of the generating functional of [...] Read more.
A joint introduction of composite and background fields into non-Abelian quantum gauge theories is suggested based on the symmetries of the generating functional of Green’s functions, with the systematic analysis focused on quantum Yang–Mills theories, including the properties of the generating functional of vertex Green’s functions (effective action). For the effective action in such theories, gauge dependence is found in terms of a nilpotent operator with composite and background fields, and on-shell independence from gauge fixing is established. The basic concept of a joint introduction of composite and background fields into non-Abelian gauge theories is extended to the Volovich–Katanaev model of two-dimensional gravity with dynamical torsion, as well as to the Gribov–Zwanziger theory. Full article
(This article belongs to the Special Issue Quantum Gravity Condensates)
12 pages, 275 KiB  
Article
Violation of the Dominant Energy Condition in Geometrodynamics
by Vladimir Lasukov
Symmetry 2020, 12(3), 400; https://doi.org/10.3390/sym12030400 - 4 Mar 2020
Cited by 4 | Viewed by 2595
Abstract
It is shown that in Einstein’s theory and in the theory of gravity with Logunov constraints, there is a field-theoretical model of dark energy that is consistent with the observational data indicating that the Hubble value increases over time. In the developed model [...] Read more.
It is shown that in Einstein’s theory and in the theory of gravity with Logunov constraints, there is a field-theoretical model of dark energy that is consistent with the observational data indicating that the Hubble value increases over time. In the developed model of dark energy, the isotropic energy dominant condition is violated. It solves the problem of the cosmological singularity and the singularity of “black holes”. The compact configuration of the scalar field can generate a flux of particles by the pairs of particles production mechanism from the vacuum by a field of barrier and in the process of transformation of thermal energy (Hawking radiation) and acceleration energy into radiation. The scalars can play the role of the so-called “black holes” with no singularity inside themselves. Full article
(This article belongs to the Special Issue Quantum Gravity Condensates)
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