Special Issue "Quantum Gravity Phenomenology"

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Foundations of Quantum Mechanics and Quantum Gravity".

Deadline for manuscript submissions: closed (10 July 2022) | Viewed by 6013

Special Issue Editors

Dr. Arundhati Dasgupta
E-Mail Website
Guest Editor
Department of Physics and Astronomy, University of Lethbridge, Lethbridge, AB, Canada
Interests: theoretical physics; quantum gravity theory and phenomenology; astrophysics; gravitational waves
Prof. Dr. Alfredo Iorio
E-Mail Website
Guest Editor
Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 18000 Prague 8, Czech Republic
Interests: Theoretical Physics; Quantum Field Theory in flat and curved space; Condensed Matter; Analog Gravity on Dirac materials

Special Issue Information

Dear Colleagues,

Quantum gravity is expected to be important at Planck lengths, i.e., 10−33 cm. However, indirect effects might be observed in astrophysical phenomena, cosmological observations, and “in the lab” experiments. It is important to study such effects and design/predict experiments which will confirm the existence of a quantum theory of gravity. With gravitational waves providing a new window of observation to the physics of the Universe, we expect that gravitons or quantized gravitational waves will also be discovered. At this time, an issue devoted to quantum gravity phenomenology will be important.

Dr. Arundhati Dasgupta
Prof. Alfredo Iorio
Guest Editors

Manuscript Submission Information

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Keywords

  • quantum gravity phenomenology
  • analog models of gravity
  • gravitational waves and gravitons
  • signatures of quantum gravity in astrophysics
  • quantum cosmology
  • observational cosmology
  • curved graphene
  • quantum gravity on the graphene

Published Papers (10 papers)

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Research

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Article
Phenomenological Inflationary Model in Supersymmetric Quantum Cosmology
Universe 2022, 8(8), 414; https://doi.org/10.3390/universe8080414 - 06 Aug 2022
Viewed by 169
Abstract
We consider the effective evolution of a phenomenological model from FLRW supersymmetric quantum cosmology with a scalar field. The scalar field acts as a clock and inflaton. We examine a family of simple superpotentials that produce an inflation whose virtual effect on inhomogeneous [...] Read more.
We consider the effective evolution of a phenomenological model from FLRW supersymmetric quantum cosmology with a scalar field. The scalar field acts as a clock and inflaton. We examine a family of simple superpotentials that produce an inflation whose virtual effect on inhomogeneous fluctuations shows very good agreement with PLANCK observational evidence for the tensor-to-scalar ratio and the scalar spectral index. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Article
On the Hilbert Space in Quantum Gravity
Universe 2022, 8(8), 413; https://doi.org/10.3390/universe8080413 - 05 Aug 2022
Viewed by 263
Abstract
This article deals with the fractional problem of Sturm–Liouville and the Hilbert space associated with the solutions of this differential equation. We apply a quantization procedure to Schwarzschild space–time and obtain a fractional differential equation. The Hilbert space for these solutions is established. [...] Read more.
This article deals with the fractional problem of Sturm–Liouville and the Hilbert space associated with the solutions of this differential equation. We apply a quantization procedure to Schwarzschild space–time and obtain a fractional differential equation. The Hilbert space for these solutions is established. We used equations arising from quantization for the FRW and Reissner–Nordstron metrics to build the respective Hilbert spaces. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Article
A Unified Quantization of Gravity and Other Fundamental Forces of Nature
Universe 2022, 8(8), 404; https://doi.org/10.3390/universe8080404 - 01 Aug 2022
Viewed by 237
Abstract
We quantized the interaction of gravity with Yang–Mills and spinor fields; hence, offering a quantum theory incorporating all four fundamental forces of nature. Let us abbreviate the spatial Hamilton functions of the standard model by HSM and the Hamilton function of [...] Read more.
We quantized the interaction of gravity with Yang–Mills and spinor fields; hence, offering a quantum theory incorporating all four fundamental forces of nature. Let us abbreviate the spatial Hamilton functions of the standard model by HSM and the Hamilton function of gravity by HG. Working in a fiber bundle E with base space S0=Rn, where the fiber elements are Riemannian metrics, we can express the Hamilton functions in the form HG+HSM=HG+t23H˜SM, if n=3, where H˜SM depends on metrics σij satisfying detσij=1. In the quantization process, we quantize HG for general σij but H˜SM only for σij=δij by the usual methods of QFT. Let v resp. ψ be the spatial eigendistributions of the respective Hamilton operators, then, the solutions u of the Wheeler–DeWitt equation are given by u=wvψ, where w satisfies an ODE and u is evaluated at (t,δij) in the fibers. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Article
Massive Neutron Stars and White Dwarfs as Noncommutative Fuzzy Spheres
Universe 2022, 8(8), 388; https://doi.org/10.3390/universe8080388 - 22 Jul 2022
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Abstract
Over the last couple of decades, there have been direct and indirect evidences for massive compact objects than their conventional counterparts. A couple of such examples are super-Chandrasekhar white dwarfs and massive neutron stars. The observations of more than a dozen peculiar over-luminous [...] Read more.
Over the last couple of decades, there have been direct and indirect evidences for massive compact objects than their conventional counterparts. A couple of such examples are super-Chandrasekhar white dwarfs and massive neutron stars. The observations of more than a dozen peculiar over-luminous type Ia supernovae predict their origins from super-Chandrasekhar white dwarf progenitors. On the other hand, recent gravitational wave detection and some pulsar observations provide arguments for massive neutron stars, lying in the famous mass-gap between lowest astrophysical black hole and conventional highest neutron star masses. We show that the idea of a squashed fuzzy sphere, which brings in noncommutative geometry, can self-consistently explain either of the massive objects as if they are actually fuzzy or squashed fuzzy spheres. Noncommutative geometry is a branch of quantum gravity. If the above proposal is correct, it will provide observational evidences for noncommutativity. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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Communication
Analogue Quantum Gravity in Hyperbolic Metamaterials
Universe 2022, 8(4), 242; https://doi.org/10.3390/universe8040242 - 14 Apr 2022
Cited by 1 | Viewed by 665
Abstract
It is well known that extraordinary photons in hyperbolic metamaterials may be described as living in an effective Minkowski spacetime, which is defined by the peculiar form of the strongly anisotropic dielectric tensor in these metamaterials. Here, we demonstrate that within the scope [...] Read more.
It is well known that extraordinary photons in hyperbolic metamaterials may be described as living in an effective Minkowski spacetime, which is defined by the peculiar form of the strongly anisotropic dielectric tensor in these metamaterials. Here, we demonstrate that within the scope of this approximation, the sound waves in hyperbolic metamaterials look similar to gravitational waves, and therefore the quantized sound waves (phonons) look similar to gravitons. Such an analogue model of quantum gravity looks especially interesting near the phase transitions in hyperbolic metamaterials where it becomes possible to switch quantum gravity effects on and off as a function of metamaterial temperature. We also predict strong enhancement of sonoluminescence in ferrofluid-based hyperbolic metamaterials, which looks analogous to particle creation in strong gravitational fields. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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Article
Lorentzian Vacuum Transitions in Hořava–Lifshitz Gravity
Universe 2022, 8(4), 237; https://doi.org/10.3390/universe8040237 - 12 Apr 2022
Cited by 1 | Viewed by 574
Abstract
The vacuum transition probabilities for a Friedmann–Lemaître–Robertson–Walker universe with positive curvature in Hořava–Lifshitz gravity in the presence of a scalar field potential in the Wentzel–Kramers–Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to [...] Read more.
The vacuum transition probabilities for a Friedmann–Lemaître–Robertson–Walker universe with positive curvature in Hořava–Lifshitz gravity in the presence of a scalar field potential in the Wentzel–Kramers–Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to the Wheeler–DeWitt equation presented in a previous work. We consider two situations of scalar fields, one in which the scalar field depends on all the spacetime variables and another in which the scalar field depends only on the time variable. In both cases, analytic expressions for the vacuum transition probabilities are obtained, and the infrared and ultraviolet limits are discussed for comparison with the result obtained by using general relativity. For the case in which the scalar field depends on all spacetime variables, we observe that in the infrared limit it is possible to obtain a similar behavior as in general relativity, however, in the ultraviolet limit the behavior found is completely opposite. Some few comments about possible phenomenological implications of our results are given. One of them is a plausible resolution of the initial singularity. On the other hand, for the case in which the scalar field depends only on the time variable, the behavior coincides with that of general relativity in both limits, although in the intermediate region the probability is slightly altered. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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Article
Considerations on Quantum Gravity Phenomenology
Universe 2021, 7(11), 439; https://doi.org/10.3390/universe7110439 - 15 Nov 2021
Cited by 2 | Viewed by 693
Abstract
I describe two phenomenological windows on quantum gravity that seem promising to me. I argue that we already have important empirical inputs that should orient research in quantum gravity. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Communication
Spin Distribution for the ’t Hooft–Polyakov Monopole in the Geometric Theory of Defects
Universe 2021, 7(8), 256; https://doi.org/10.3390/universe7080256 - 21 Jul 2021
Cited by 1 | Viewed by 559
Abstract
Recently the ’t Hooft–Polyakov monopole solutions in Yang–Mills theory were given new physical interpretation in the geometric theory of defects describing the continuous distribution of dislocations and disclinations in elastic media. It means that the ’t Hooft–Polyakov monopole can be seen, probably, in [...] Read more.
Recently the ’t Hooft–Polyakov monopole solutions in Yang–Mills theory were given new physical interpretation in the geometric theory of defects describing the continuous distribution of dislocations and disclinations in elastic media. It means that the ’t Hooft–Polyakov monopole can be seen, probably, in solids. To this end we need to compute the corresponding spin distribution on lattice sites of crystals. The paper describes one of the possible spin distributions. The Bogomol’nyi–Prasad–Sommerfield solution is considered as an example. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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Review

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Review
Maximal Kinematical Invariance Group of Fluid Dynamics and Applications
Universe 2022, 8(6), 319; https://doi.org/10.3390/universe8060319 - 07 Jun 2022
Cited by 2 | Viewed by 376
Abstract
The maximal kinematical invariance group of the Euler equations of fluid dynamics for the standard polytropic exponent is larger than the Galilei group. Specifically, the inversion transformation [...] Read more.
The maximal kinematical invariance group of the Euler equations of fluid dynamics for the standard polytropic exponent is larger than the Galilei group. Specifically, the inversion transformation (Σ:t1/t,xx/t) leaves the Euler equation’s invariant. This duality has been used to explain the striking similarities observed in simulations of the supernova explosions and laboratory implosions induced in plasma by intense lasers. The inversion symmetry extends to discontinuous fluid flows as well. In this contribution, we provide a concise review of these ideas and discuss some applications. We also explicitly work out the implosion dual of the Sedov’s explosion solution. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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Review
Space–Time Physics in Background-Independent Theories of Quantum Gravity
Universe 2021, 7(7), 251; https://doi.org/10.3390/universe7070251 - 20 Jul 2021
Cited by 2 | Viewed by 750
Abstract
Background independence is often emphasized as an important property of a quantum theory of gravity that takes seriously the geometrical nature of general relativity. In a background-independent formulation, quantum gravity should determine not only the dynamics of space–time but also its geometry, which [...] Read more.
Background independence is often emphasized as an important property of a quantum theory of gravity that takes seriously the geometrical nature of general relativity. In a background-independent formulation, quantum gravity should determine not only the dynamics of space–time but also its geometry, which may have equally important implications for claims of potential physical observations. One of the leading candidates for background-independent quantum gravity is loop quantum gravity. By combining and interpreting several recent results, it is shown here how the canonical nature of this theory makes it possible to perform a complete space–time analysis in various models that have been proposed in this setting. In spite of the background-independent starting point, all these models turned out to be non-geometrical and even inconsistent to varying degrees, unless strong modifications of Riemannian geometry are taken into account. This outcome leads to several implications for potential observations as well as lessons for other background-independent approaches. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
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