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Universe, Volume 6, Issue 11 (November 2020) – 32 articles

Cover Story (view full-size image): Important but not so well-known historical issues around the crucial discovery of the universe expansion and, at the other extreme, present attempts at determining the cosmic expansion rate are discussed, all in accordance with General Relativity, of which a brief pedagogical introduction is here provided, too. Another crucial question is: What drives the acceleration of the universe’s expansion? This is called dark energy, but what is it actually? It could be the result of a sort of Casimir effect at the cosmological level, a theroy which has yet not been discarded. Some technical problems in tackling this issue are the regularization and renormalization procedures involved. Beautiful, albeit non-trivial mathematics, which use the zeta function of operators associated with physical quantities, are key in this respect. A very brief discussion of those items is also given. View this paper.
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12 pages, 576 KiB  
Article
Neutron Star Properties: Quantifying the Effect of the Crust–Core Matching Procedure
by Márcio Ferreira and Constança Providência
Universe 2020, 6(11), 220; https://doi.org/10.3390/universe6110220 - 23 Nov 2020
Cited by 7 | Viewed by 1791
Abstract
The impact of the equation of state (EoS) crust-core matching procedure on neutron star (NS) properties is analyzed within a meta-modeling approach. Using a Taylor expansion to parametrize the core equation of state (EoS) and the SLy4 crust EoS, we create two distinct [...] Read more.
The impact of the equation of state (EoS) crust-core matching procedure on neutron star (NS) properties is analyzed within a meta-modeling approach. Using a Taylor expansion to parametrize the core equation of state (EoS) and the SLy4 crust EoS, we create two distinct EoS datasets employing two matching procedures. Each EoS describes cold NS matter in a β equilibrium that is thermodynamically stable and causal. It is shown that the crust-core matching procedure affects not only the crust-core transition but also the nuclear matter parameter space of the core EoS, and thus the most probable nuclear matter properties. An uncertainty of as much as 5% (8%) on the determination of low mass NS radii (tidal deformability) is attributed to the complete matching procedure, including the effect on core EoS. By restricting the analysis, imposing that the same set of core EoS is retained in both matching procedures, the uncertainty on the NS radius drops to 3.5% and below 1.5% for 1.9M. Moreover, under these conditions, the crust-core matching procedure has a strong impact on the Love number k2, of almost 20% for 1.0M stars and 7% for 1.9M stars, but it shows a very small impact on the tidal deformability Λ, below 1%. Full article
(This article belongs to the Special Issue Neutron Star Astrophysics)
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25 pages, 769 KiB  
Article
X-ray Properties of 3C 111: Separation of Primary Nuclear Emission and Jet Continuum
by Elena Fedorova, B.I. Hnatyk, V.I. Zhdanov and A. Del Popolo
Universe 2020, 6(11), 219; https://doi.org/10.3390/universe6110219 - 21 Nov 2020
Cited by 3 | Viewed by 1848
Abstract
3C111 is BLRG with signatures of both FSRQ and Sy1 in X-ray spectrum. The significant X-ray observational dataset was collected for it by INTEGRAL, XMM-Newton, SWIFT, Suzaku and others. The overall X-ray spectrum of 3C 111 shows signs of a peculiarity with the [...] Read more.
3C111 is BLRG with signatures of both FSRQ and Sy1 in X-ray spectrum. The significant X-ray observational dataset was collected for it by INTEGRAL, XMM-Newton, SWIFT, Suzaku and others. The overall X-ray spectrum of 3C 111 shows signs of a peculiarity with the large value of the high-energy cut-off typical rather for RQ AGN, probably due to the jet contamination. Separating the jet counterpart in the X-ray spectrum of 3C 111 from the primary nuclear counterpart can answer the question is this nucleus truly peculiar or this is a fake “peculiarity” due to a significant jet contribution. In view of this question, our aim is to estimate separately the accretion disk/corona and non-thermal jet emission in the 3C 111 X-ray spectra within different observational periods. To separate the disk/corona and jet contributions in total continuum, we use the idea that radio and X-ray spectra of jet emission can be described by a simple power-law model with the same photon index. This additional information allows us to derive rather accurate values of these contributions. In order to test these results, we also consider relations between the nuclear continuum and the line emission. Full article
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24 pages, 570 KiB  
Article
String-Inspired Running Vacuum—The “Vacuumon”—And the Swampland Criteria
by Nick E. Mavromatos, Joan Solà Peracaula and Spyros Basilakos
Universe 2020, 6(11), 218; https://doi.org/10.3390/universe6110218 - 20 Nov 2020
Cited by 11 | Viewed by 1699
Abstract
We elaborate further on the compatibility of the “vacuumon potential” that characterises the inflationary phase of the running vacuum model (RVM) with the swampland criteria. The work is motivated by the fact that, as demonstrated recently by the authors, the RVM framework can [...] Read more.
We elaborate further on the compatibility of the “vacuumon potential” that characterises the inflationary phase of the running vacuum model (RVM) with the swampland criteria. The work is motivated by the fact that, as demonstrated recently by the authors, the RVM framework can be derived as an effective gravitational field theory stemming from underlying microscopic (critical) string theory models with gravitational anomalies, involving condensation of primordial gravitational waves. Although believed to be a classical scalar field description, not representing a fully fledged quantum field, we show here that the vacuumon potential satisfies certain swampland criteria for the relevant regime of parameters and field range. We link the criteria to the Gibbons–Hawking entropy that has been argued to characterise the RVM during the de Sitter phase. These results imply that the vacuumon may, after all, admit under certain conditions, a rôle as a quantum field during the inflationary (almost de Sitter) phase of the running vacuum. The conventional slow-roll interpretation of this field, however, fails just because it satisfies the swampland criteria. The RVM effective theory derived from the low-energy effective action of string theory does, however, successfully describe inflation thanks to the H4 terms induced by the gravitational anomalous condensates. In addition, the stringy version of the RVM involves the Kalb–Ramond (KR) axion field, which, in contrast to the vacuumon, does perfectly satisfy the slow-roll condition. We conclude that the vacuumon description is not fully equivalent to the stringy formulation of the RVM. Our study provides a particularly interesting example of a successful phenomenological theory beyond the ΛCDM, such as the RVM, in which the fulfilment of the swampland criteria by the associated scalar field potential, along with its compatibility with (an appropriate form of) the weak gravity conjecture, prove to be insufficient conditions for warranting consistency of the scalar vacuum field representation as a faithful ultraviolet complete representation of the RVM at the quantum gravity level. Full article
(This article belongs to the Section Cosmology)
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16 pages, 288 KiB  
Review
Nuclear Response to Second-Order Isospin Probes in Connection to Double Beta Decay
by Francesco Cappuzzello and Manuela Cavallaro
Universe 2020, 6(11), 217; https://doi.org/10.3390/universe6110217 - 20 Nov 2020
Cited by 6 | Viewed by 1740
Abstract
One of the key ingredients needed to extract quantitative information on neutrino absolute mass scale from the possible measurement of the neutrinoless double-beta (0νββ) decay half-lives is the nuclear matrix element (NME) characterizing such transitions. NMEs are not physical observables and can only [...] Read more.
One of the key ingredients needed to extract quantitative information on neutrino absolute mass scale from the possible measurement of the neutrinoless double-beta (0νββ) decay half-lives is the nuclear matrix element (NME) characterizing such transitions. NMEs are not physical observables and can only be deduced by theoretical calculations. However, since the atomic nuclei involved in the decay are many-body systems, only approximated values are available to date. In addition, the value of the coupling constants to be used for the weak interaction vertices is still an open question, which introduces a further indetermination in the calculations of NMEs. Several experimental approaches were developed in the years with the aim of providing useful information to further constrain the theory. Here we give an overview of the role of charge exchange reactions in this scenario, focusing on second-order processes, namely the double charge exchange (DCE) reactions. Full article
(This article belongs to the Special Issue Neutrinoless Double Beta Decay)
26 pages, 342 KiB  
Article
Density Operator Approach to Turbulent Flows in Plasma and Atmospheric Fluids
by Konstantin G. Zloshchastiev
Universe 2020, 6(11), 216; https://doi.org/10.3390/universe6110216 - 20 Nov 2020
Cited by 3 | Viewed by 1709
Abstract
We formulate a statistical wave-mechanical approach to describe dissipation and instabilities in two-dimensional turbulent flows of magnetized plasmas and atmospheric fluids, such as drift and Rossby waves. This is made possible by the existence of Hilbert space, associated with the electric potential of [...] Read more.
We formulate a statistical wave-mechanical approach to describe dissipation and instabilities in two-dimensional turbulent flows of magnetized plasmas and atmospheric fluids, such as drift and Rossby waves. This is made possible by the existence of Hilbert space, associated with the electric potential of plasma or stream function of atmospheric fluid. We therefore regard such turbulent flows as macroscopic wave-mechanical phenomena, driven by the non-Hermitian Hamiltonian operator we derive, whose anti-Hermitian component is attributed to an effect of the environment. Introducing a wave-mechanical density operator for the statistical ensembles of waves, we formulate master equations and define observables: such as the enstrophy and energy of both the waves and zonal flow as statistical averages. We establish that our open system can generally follow two types of time evolution, depending on whether the environment hinders or assists the system’s stability and integrity. We also consider a phase-space formulation of the theory, including the geometrical-optic limit and beyond, and study the conservation laws of physical observables. It is thus shown that the approach predicts various mechanisms of energy and enstrophy exchange between drift waves and zonal flow, which were hitherto overlooked in models based on wave kinetic equations. Full article
22 pages, 3350 KiB  
Article
The Line-of-Sight Analysis of Spatial Distribution of Galaxies in the COSMOS2015 Catalogue
by Maxim Nikonov, Mikhail Chekal, Stanislav Shirokov, Andrey Baryshev and Vladimir Gorokhov
Universe 2020, 6(11), 215; https://doi.org/10.3390/universe6110215 - 20 Nov 2020
Cited by 1 | Viewed by 1661
Abstract
New observations of high-redshift objects are crucial for the improvement of the standard ΛCDM cosmological model and our understanding of the Universe. One of the main directions of modern observational cosmology is the analysis of the large-scale structure of Universe, in particular, [...] Read more.
New observations of high-redshift objects are crucial for the improvement of the standard ΛCDM cosmological model and our understanding of the Universe. One of the main directions of modern observational cosmology is the analysis of the large-scale structure of Universe, in particular, in deep fields. We study the large-scale structure of the Universe along the line of sight using the latest version of the COSMOS2015 catalogue, which contains 518,404 high quality photometric redshifts of galaxies selected in the optical range of the COSMOS field (2×2 deg2), with depth up to the redshift z6. We analyze large-scale fluctuations in the number of galaxies along the line of sight and provide an estimate of the average linear sizes of the self-correlating fluctuations (structures) in independent redshift bins of Δz=0.1 along with the estimate of the standard deviation from homogeneity (the observed cosmic variance). We suggest a new method of the line-of-sight analysis based on previous works and formulate further prospects of method development. For the case of the theoretical form of approximation of homogeneity in the ΛCDM framework, the average standard deviation of detected structures from homogeneity is σmeanΛCDM=0.09±0.02, and the average characteristic size of structures is RmeanΛCDM=790±150 Mpc. For the case of the empirical approximation of homogeneity, the average standard deviation of detected structures from homogeneity is σmeanempiric=0.08±0.01, and the average characteristic size of structures is Rmeanempiric=640±140 Mpc. Full article
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9 pages, 233 KiB  
Communication
On the Collision of Relativistic Shock Waves and the Large Scale Structure of the Universe
by Alexander Golubiatnikov and Daniil Lyuboshits
Universe 2020, 6(11), 214; https://doi.org/10.3390/universe6110214 - 20 Nov 2020
Cited by 1 | Viewed by 1355
Abstract
The solution to the problem of symmetric collision of two relativistic shock waves is given and limiting cases are investigated: Newtonian mechanics and ultrarelativistic mechanics. The results are correlated with the presence of known superclusters and "walls" in the Universe. Full article
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12 pages, 1333 KiB  
Communication
The Reconstruction of Non-Minimal Derivative Coupling Inflationary Potentials
by Qin Fei, Zhu Yi and Yingjie Yang
Universe 2020, 6(11), 213; https://doi.org/10.3390/universe6110213 - 19 Nov 2020
Cited by 9 | Viewed by 2334
Abstract
We derive the reconstruction formulae for the inflation model with the non-minimal derivative coupling term. If reconstructing the potential from the tensor-to-scalar ratio r, we could obtain the potential without using the high friction limit. As an example, we reconstruct the potential [...] Read more.
We derive the reconstruction formulae for the inflation model with the non-minimal derivative coupling term. If reconstructing the potential from the tensor-to-scalar ratio r, we could obtain the potential without using the high friction limit. As an example, we reconstruct the potential from the parameterization r=8α/(N+β)γ, which is a general form of the α-attractor. The reconstructed potential has the same asymptotic behavior as the T- and E-model if we choose γ=2 and α1. We also discuss the constraints from the reheating phase by assuming the parameter wre of state equation during reheating is a constant. The scale of big-bang nucleosynthesis could put an upper limit on ns if wre=2/3 and a low limit on ns if wre=1/6. Full article
(This article belongs to the Special Issue Inflation, Black Holes and Gravitational Waves)
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92 pages, 1446 KiB  
Review
Einstein’s Geometrical versus Feynman’s Quantum-Field Approaches to Gravity Physics: Testing by Modern Multimessenger Astronomy
by Yurij Baryshev
Universe 2020, 6(11), 212; https://doi.org/10.3390/universe6110212 - 18 Nov 2020
Cited by 14 | Viewed by 3952
Abstract
Modern multimessenger astronomy delivers unique opportunity for performing crucial observations that allow for testing the physics of the gravitational interaction. These tests include detection of gravitational waves by advanced LIGO-Virgo antennas, Event Horizon Telescope observations of central relativistic compact objects (RCO) in active [...] Read more.
Modern multimessenger astronomy delivers unique opportunity for performing crucial observations that allow for testing the physics of the gravitational interaction. These tests include detection of gravitational waves by advanced LIGO-Virgo antennas, Event Horizon Telescope observations of central relativistic compact objects (RCO) in active galactic nuclei (AGN), X-ray spectroscopic observations of Fe Kα line in AGN, Galactic X-ray sources measurement of masses and radiuses of neutron stars, quark stars, and other RCO. A very important task of observational cosmology is to perform large surveys of galactic distances independent on cosmological redshifts for testing the nature of the Hubble law and peculiar velocities. Forthcoming multimessenger astronomy, while using such facilities as advanced LIGO-Virgo, Event Horizon Telescope (EHT), ALMA, WALLABY, JWST, EUCLID, and THESEUS, can elucidate the relation between Einstein’s geometrical and Feynman’s quantum-field approaches to gravity physics and deliver a new possibilities for unification of gravitation with other fundamental quantum physical interactions. Full article
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11 pages, 281 KiB  
Communication
Kinematics and Selection Rules for Light-by-Light Scattering in a Strong Magnetic Field
by Anatoly Shabad
Universe 2020, 6(11), 211; https://doi.org/10.3390/universe6110211 - 17 Nov 2020
Cited by 1 | Viewed by 1241
Abstract
Selection rules that follow from parity and four-momentum conservation are listed for head-on light-by-light scattering in a strong magnetic field taking into account nontrivial dispersion laws of different photon eigen-modes. The wave-length shifts occur for certain transitions between photon eigen-modes. Full article
(This article belongs to the Special Issue Development of Modern Methods of QFT and Their Applications)
18 pages, 341 KiB  
Article
Extremal Cosmological Black Holes in Horndeski Gravity and the Anti-Evaporation Regime
by Ismael Ayuso and Diego Sáez-Chillón Gómez
Universe 2020, 6(11), 210; https://doi.org/10.3390/universe6110210 - 17 Nov 2020
Viewed by 1338
Abstract
Extremal cosmological black holes are analysed in the framework of the most general second order scalar-tensor theory, the so-called Horndeski gravity. Such extremal black holes are a particular case of Schwarzschild-De Sitter black holes that arises when the black hole horizon and the [...] Read more.
Extremal cosmological black holes are analysed in the framework of the most general second order scalar-tensor theory, the so-called Horndeski gravity. Such extremal black holes are a particular case of Schwarzschild-De Sitter black holes that arises when the black hole horizon and the cosmological one coincide. Such metric is induced by a particular value of the effective cosmological constant and is known as Nariai spacetime. The existence of this type of solutions is studied when considering the Horndeski Lagrangian and its stability is analysed, where the so-called anti-evaporation regime is studied. Contrary to other frameworks, the radius of the horizon remains stable for some cases of the Horndeski Lagrangian when considering perturbations at linear order. Full article
(This article belongs to the Section Gravitation)
21 pages, 405 KiB  
Article
Modified Newtonian Gravity, Wide Binaries and the Tully-Fisher Relation
by Luis Acedo
Universe 2020, 6(11), 209; https://doi.org/10.3390/universe6110209 - 14 Nov 2020
Cited by 6 | Viewed by 2519
Abstract
A recent study of a sample of wide binary star systems from the Hipparcos and Gaia catalogues has found clear evidence of a gravitational anomaly of the same kind as that appearing in galaxies and galactic clusters. Instead of a relative orbital velocity [...] Read more.
A recent study of a sample of wide binary star systems from the Hipparcos and Gaia catalogues has found clear evidence of a gravitational anomaly of the same kind as that appearing in galaxies and galactic clusters. Instead of a relative orbital velocity decaying as the square root of the separation, ΔVr1/2, it was shown that an asymptotic constant velocity is reached for distances of order 0.1 pc. If confirmed, it would be difficult to accommodate this breakdown of Kepler’s laws within the current dark matter (DM) paradigm because DM does not aggregate in small scales, so there would be very little DM in a 0.1 pc sphere. In this paper, we propose a simple non-Newtonian model of gravity that could explain both the wide binaries anomaly and the anomalous rotation curves of galaxies as codified by the Tully-Fisher relation. The required extra potential can be understood as a Klein-Gordon field with a position-dependent mass parameter. The extra forces behave as 1/r on parsec scales and r on Solar system scales. We show that retrograde anomalous perihelion precessions are predicted for the planets. This could be tested by precision ephemerides in the near future. Full article
(This article belongs to the Special Issue Universe: 5th Anniversary)
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20 pages, 579 KiB  
Article
BCS-BEC Crossover Effects and Pseudogap in Neutron Matter
by David Durel and Michael Urban
Universe 2020, 6(11), 208; https://doi.org/10.3390/universe6110208 - 13 Nov 2020
Cited by 6 | Viewed by 1704
Abstract
Due to the large neutron–neutron scattering length, dilute neutron matter resembles the unitary Fermi gas, which lies half-way in the crossover from the BCS phase of weakly coupled Cooper pairs to the Bose–Einstein condensate of dimers. We discuss crossover effects in analogy with [...] Read more.
Due to the large neutron–neutron scattering length, dilute neutron matter resembles the unitary Fermi gas, which lies half-way in the crossover from the BCS phase of weakly coupled Cooper pairs to the Bose–Einstein condensate of dimers. We discuss crossover effects in analogy with the T-matrix theory used in the physics of ultracold atoms, which we generalize to the case of a non-separable finite-range interaction. A problem of the standard Nozières–Schmitt-Rink approach and different ways to solve it are discussed. It is shown that in the strong-coupling regime, the spectral function exhibits a pseudo-gap at temperatures above the critical temperature Tc. The effect of the correlated density on the density dependence of Tc is found to be rather weak, but a possibly important effect due to the reduced quasiparticle weight is identified. Full article
(This article belongs to the Special Issue Superfluidity and Superconductivity in Neutron Stars)
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17 pages, 403 KiB  
Article
Discerning the Nature of Neutrinos: Decoherence and Geometric Phases
by Antonio Capolupo, Salvatore Marco Giampaolo, Gaetano Lambiase and Aniello Quaranta
Universe 2020, 6(11), 207; https://doi.org/10.3390/universe6110207 - 13 Nov 2020
Cited by 11 | Viewed by 2001
Abstract
We present new approaches to distinguish between Dirac and Majorana neutrinos. The first is based on the analysis of the geometric phases associated to neutrinos in matter, the second on the effects of decoherence on neutrino oscillations. In the former we compute the [...] Read more.
We present new approaches to distinguish between Dirac and Majorana neutrinos. The first is based on the analysis of the geometric phases associated to neutrinos in matter, the second on the effects of decoherence on neutrino oscillations. In the former we compute the total and geometric phase for neutrinos, and find that they depend on the Majorana phase and on the parametrization of the mixing matrix. In the latter, we show that Majorana neutrinos might violate CPT symmetry, whereas Dirac neutrinos preserve CPT. A phenomenological analysis is also reported showing the possibility to highlight the distinctions between Dirac and Majorana neutrinos. Full article
(This article belongs to the Special Issue Universe: 5th Anniversary)
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17 pages, 754 KiB  
Article
Comparison between the Thomas–Fermi and Hartree–Fock–Bogoliubov Methods in the Inner Crust of a Neutron Star: The Role of Pairing Correlations
by Matthew Shelley and Alessandro Pastore
Universe 2020, 6(11), 206; https://doi.org/10.3390/universe6110206 - 11 Nov 2020
Cited by 12 | Viewed by 1966
Abstract
We investigated the role of a pairing correlation in the chemical composition of the inner crust of a neutron star with the extended Thomas–Fermi method, using the Strutinsky integral correction. We compare our results with the fully self-consistent Hartree–Fock–Bogoliubov approach, showing that the [...] Read more.
We investigated the role of a pairing correlation in the chemical composition of the inner crust of a neutron star with the extended Thomas–Fermi method, using the Strutinsky integral correction. We compare our results with the fully self-consistent Hartree–Fock–Bogoliubov approach, showing that the resulting discrepancy, apart from the very low density region, is compatible with the typical accuracy we can achieve with standard mean-field methods. Full article
(This article belongs to the Special Issue Superfluidity and Superconductivity in Neutron Stars)
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30 pages, 1136 KiB  
Article
Radiation Problems Accompanying Carrier Production by an Electric Field in the Graphene
by Sergei P. Gavrilov, Dmitry M. Gitman, Vadim V. Dmitriev, Anatolii D. Panferov and Stanislav A. Smolyansky
Universe 2020, 6(11), 205; https://doi.org/10.3390/universe6110205 - 06 Nov 2020
Cited by 4 | Viewed by 1682
Abstract
A number of physical processes that occur in a flat one-dimensional graphene structure under the action of strong time-dependent electric fields are considered. It is assumed that the Dirac model can be applied to the graphene as a subsystem of the general system [...] Read more.
A number of physical processes that occur in a flat one-dimensional graphene structure under the action of strong time-dependent electric fields are considered. It is assumed that the Dirac model can be applied to the graphene as a subsystem of the general system under consideration, which includes an interaction with quantized electromagnetic field. The Dirac model itself in the external electromagnetic field (in particular, the behavior of charged carriers) is treated nonperturbatively with respect to this field within the framework of strong-field QED with unstable vacuum. This treatment is combined with a kinetic description of the radiation of photons from the electron-hole plasma created from the vacuum under the action of the electric field. An interaction with quantized electromagnetic field is described perturbatively. A significant development of the kinetic equation formalism is presented. A number of specific results are derived in the course of analytical and numerical study of the equations. We believe that some of predicted effects and properties of considered processes may be verified experimentally. Among these effects, it should be noted a characteristic spectral composition anisotropy of the quantum radiation and a possible presence of even harmonics of the external field in the latter radiation. Full article
(This article belongs to the Special Issue Development of Modern Methods of QFT and Their Applications)
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15 pages, 513 KiB  
Article
Saturation of Energy Levels of the Hydrogen Atom in Strong Magnetic Field
by Tiago C. Adorno, Dmitry M. Gitman and Anatoly E. Shabad
Universe 2020, 6(11), 204; https://doi.org/10.3390/universe6110204 - 05 Nov 2020
Viewed by 2223
Abstract
We demonstrate that the finiteness of the limiting values of the lower energy levels of a hydrogen atom under an unrestricted growth of the magnetic field, into which this atom is embedded, is achieved already when the vacuum polarization (VP) is calculated in [...] Read more.
We demonstrate that the finiteness of the limiting values of the lower energy levels of a hydrogen atom under an unrestricted growth of the magnetic field, into which this atom is embedded, is achieved already when the vacuum polarization (VP) is calculated in the magnetic field within the approximation of the local action of Euler–Heisenberg. We find that the mechanism for this saturation is different from the one acting, when VP is calculated via the Feynman diagram in the Furry picture. We study the effective potential that appears when the adiabatic (diagonal) approximation is exploited for solving the Schrödinger equation for the longitudinal degree of freedom of the electron on the lowest Landau level in the atom. We find that the (effective) potential of a point-like charge remains nonsingular thanks to the growing screening provided by VP. The regularizing length turns out to be α/3π¯λC, where ¯λC is the electron Compton length. The family of effective potentials, labeled by growing values of the magnetic field condenses towards a certain limiting, magnetic-field-independent potential-distance curve. The limiting values of even ground-state energies are determined for four magnetic quantum numbers using the Karnakov–Popov method. Full article
(This article belongs to the Special Issue Development of Modern Methods of QFT and Their Applications)
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18 pages, 571 KiB  
Article
Self-Adjoint Extension Approach to Motion of Spin-1/2 Particle in the Presence of External Magnetic Fields in the Spinning Cosmic String Spacetime
by Márcio M. Cunha and Edilberto O. Silva
Universe 2020, 6(11), 203; https://doi.org/10.3390/universe6110203 - 04 Nov 2020
Cited by 4 | Viewed by 1653
Abstract
In this work, we study the relativistic quantum motion of an electron in the presence of external magnetic fields in the spinning cosmic string spacetime. The approach takes into account the terms that explicitly depend on the particle spin in the Dirac equation. [...] Read more.
In this work, we study the relativistic quantum motion of an electron in the presence of external magnetic fields in the spinning cosmic string spacetime. The approach takes into account the terms that explicitly depend on the particle spin in the Dirac equation. The inclusion of the spin element in the solution of the problem reveals that the energy spectrum is modified. We determine the energies and wave functions using the self-adjoint extension method. The technique used is based on boundary conditions allowed by the system. We investigate the profiles of the energies found. We also investigate some particular cases for the energies and compare them with the results in the literature. Full article
(This article belongs to the Special Issue Singularities in Spacetime)
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14 pages, 341 KiB  
Article
Conformal Anomaly in Yang-Mills Theory and Thermodynamics of Open Confining Strings
by Maxim N. Chernodub
Universe 2020, 6(11), 202; https://doi.org/10.3390/universe6110202 - 31 Oct 2020
Cited by 1 | Viewed by 1778
Abstract
We discuss thermodynamic properties of open confining strings introduced via static sources in the vacuum of Yang-Mills theory. We derive new sum rules for the chromoelectric and chromomagnetic condensates and use them to show that the presence of the confining string lowers the [...] Read more.
We discuss thermodynamic properties of open confining strings introduced via static sources in the vacuum of Yang-Mills theory. We derive new sum rules for the chromoelectric and chromomagnetic condensates and use them to show that the presence of the confining string lowers the gluonic pressure in the bulk of the system. The pressure deficit of the gluon plasma is related to the potential energy in the system of heavy quarks and anti-quarks in the plasma. Full article
(This article belongs to the Special Issue Development of Modern Methods of QFT and Their Applications)
18 pages, 373 KiB  
Article
Quantum Analysis of BTZ Black Hole Formation Due to the Collapse of a Dust Shell
by Alexander A. Andrianov, Artem Starodubtsev and Yasser Elmahalawy
Universe 2020, 6(11), 201; https://doi.org/10.3390/universe6110201 - 30 Oct 2020
Cited by 2 | Viewed by 1967
Abstract
We perform Hamiltonian reduction of a model in which 2 + 1 dimensional gravity with negative cosmological constant is coupled to a cylindrically symmetric dust shell. The resulting action contains only a finite number of degrees of freedom. The phase space consists of [...] Read more.
We perform Hamiltonian reduction of a model in which 2 + 1 dimensional gravity with negative cosmological constant is coupled to a cylindrically symmetric dust shell. The resulting action contains only a finite number of degrees of freedom. The phase space consists of two copies of ADS2—both coordinate and momentum space are curved. Different regions in the Penrose diagram can be identified with different patches of ADS2 momentum space. Quantization in the momentum representation becomes particularly simple in the vicinity of the horizon, where one can neglect momentum non-commutativity. In this region, we calculate the spectrum of the shell radius. This spectrum turns out to be continuous outside the horizon and becomes discrete inside the horizon with eigenvalue spacing proportional to the square root of the black hole mass. We also calculate numerically quantum transition amplitudes between different regions of the Penrose diagram in the vicinity of the horizon. This calculation shows a possibility of quantum tunneling of the shell into classically forbidden regions of the Penrose diagram, although with an exponentially damped rate away from the horizon. Full article
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11 pages, 2236 KiB  
Article
The Impact of Coronal Mass Ejections on the Seasonal Variation of the Ionospheric Critical Frequency f0F2
by Hussein M. Farid, Ramy Mawad, Essam Ghamry and Akimasa Yoshikawa
Universe 2020, 6(11), 200; https://doi.org/10.3390/universe6110200 - 30 Oct 2020
Cited by 6 | Viewed by 2005
Abstract
We investigated the relations between the monthly average values of the critical frequency (f0F2) and the physical properties of the coronal mass ejections (CMEs), then we examined the seasonal variation of f0F2 values as an impact of the [...] Read more.
We investigated the relations between the monthly average values of the critical frequency (f0F2) and the physical properties of the coronal mass ejections (CMEs), then we examined the seasonal variation of f0F2 values as an impact of the several CMEs properties. Given that, f0F2 were detected by PRJ18 (Puerto Rico) ionosonde station during the period 1996–2013. We found that the monthly average values of f0F2 are varying coherently with the sunspot number (SSN). A similar trend was found for f0F2 with the CMEs parameters such as the CME energy (linear correlation coefficient R = 0.73), width (R = 0.6) and the speed (R = 0.6). The arrived CMEs cause a plasma injection into the ionosphere, in turn, increasing the electron density, and consequently, f0F2 values. This happens in the high latitudes followed by the middle and lower latitudes. By examining the seasonal variation of f0F2, we found that the higher correlation between f0F2 and CMEs parameters occurs in the summer, then the equinoxes (spring and autumn), followed by the winter. However, the faster CMEs affect the ionosphere more efficiently in the spring more than in the summer, then the winter and the autumn seasons. Full article
(This article belongs to the Special Issue Space Weather)
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23 pages, 861 KiB  
Article
Exact and Slow-Roll Solutions for Exponential Power-Law Inflation Connected with Modified Gravity and Observational Constraints
by Igor Fomin and Sergey Chervon
Universe 2020, 6(11), 199; https://doi.org/10.3390/universe6110199 - 29 Oct 2020
Cited by 11 | Viewed by 2565
Abstract
We investigate the ability of the exponential power-law inflation to be a phenomenologically correct model of the early universe. We study General Relativity (GR) scalar cosmology equations in Ivanov–Salopek–Bond (or Hamilton–Jacobi like) representation where the Hubble parameter H is the function of a [...] Read more.
We investigate the ability of the exponential power-law inflation to be a phenomenologically correct model of the early universe. We study General Relativity (GR) scalar cosmology equations in Ivanov–Salopek–Bond (or Hamilton–Jacobi like) representation where the Hubble parameter H is the function of a scalar field ϕ. Such approach admits calculation of the potential for given H(ϕ) and consequently reconstruction of f(R) gravity in parametric form. By this manner the Starobinsky potential and non-minimal Higgs potential (and consequently the corresponding f(R) gravity) were reconstructed using constraints on the model’s parameters. We also consider methods for generalising the obtained solutions to the case of chiral cosmological models and scalar-tensor gravity. Models based on the quadratic relationship between the Hubble parameter and the function of the non-minimal interaction of the scalar field and curvature are also considered. Comparison to observation (PLANCK 2018) data shows that all models under consideration give correct values for the scalar spectral index and tensor-to-scalar ratio under a wide range of exponential-power-law model’s parameters. Full article
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16 pages, 333 KiB  
Article
Black Holes and Complexity via Constructible Universe
by Jerzy Król and Paweł Klimasara
Universe 2020, 6(11), 198; https://doi.org/10.3390/universe6110198 - 27 Oct 2020
Cited by 5 | Viewed by 1915
Abstract
The relation of randomness and classical algorithmic computational complexity is a vast and deep subject by itself. However, already, 1-randomness sequences call for quantum mechanics in their realization. Thus, we propose to approach black hole’s quantum computational complexity by classical computational classes and [...] Read more.
The relation of randomness and classical algorithmic computational complexity is a vast and deep subject by itself. However, already, 1-randomness sequences call for quantum mechanics in their realization. Thus, we propose to approach black hole’s quantum computational complexity by classical computational classes and randomness classes. The model of a general black hole is proposed based on formal tools from Zermelo–Fraenkel set theory like random forcing or minimal countable constructible model Lα. The Bekenstein–Hawking proportionality rule is shown to hold up to a multiplicative constant. Higher degrees of randomness and algorithmic computational complexity are derived in the model. Directions for further studies are also formulated. The model is designed for exploring deep quantum regime of spacetime. Full article
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40 pages, 1871 KiB  
Review
Thin-Shell Wormholes in Einstein and Einstein–Gauss–Bonnet Theories of Gravity
by Takafumi Kokubu and Tomohiro Harada
Universe 2020, 6(11), 197; https://doi.org/10.3390/universe6110197 - 26 Oct 2020
Cited by 7 | Viewed by 1967
Abstract
We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein–Gauss–Bonnet gravity. We introduce thin-shell wormholes that are categorized into a class of traversable wormhole solutions. After that, we discuss stable thin-shell wormholes with negative-tension branes in [...] Read more.
We review recent works on the possibility for eternal existence of thin-shell wormholes on Einstein and Einstein–Gauss–Bonnet gravity. We introduce thin-shell wormholes that are categorized into a class of traversable wormhole solutions. After that, we discuss stable thin-shell wormholes with negative-tension branes in Reissner–Nordström–(anti) de Sitter spacetimes in d-dimensional Einstein gravity. Imposing Z2 symmetry, we construct and classify traversable static thin-shell wormholes in spherical, planar and hyperbolic symmetries. It is found that the spherical wormholes are stable against spherically symmetric perturbations. It is also found that some classes of wormholes in planar and hyperbolic symmetries with a negative cosmological constant are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the appropriate combination of an electric charge and a negative cosmological constant. However, as special cases, there are stable wormholes even with a vanishing cosmological constant in spherical symmetry and with a vanishing electric charge in hyperbolic symmetry. Subsequently, the existence and dynamical stability of traversable thin-shell wormholes with electrically neutral negative-tension branes is discussed in Einstein–Gauss–Bonnet theory of gravitation. We consider radial perturbations against the shell for the solutions, which have the Z2 symmetry. The effect of the Gauss–Bonnet term on the stability depends on the spacetime symmetry. Full article
(This article belongs to the Special Issue Recent Advances in Wormhole Physics)
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30 pages, 1286 KiB  
Review
New Physics of Strong Interaction and Dark Universe
by Vitaly Beylin, Maxim Khlopov, Vladimir Kuksa and Nikolay Volchanskiy
Universe 2020, 6(11), 196; https://doi.org/10.3390/universe6110196 - 26 Oct 2020
Cited by 28 | Viewed by 2385
Abstract
The history of dark universe physics can be traced from processes in the very early universe to the modern dominance of dark matter and energy. Here, we review the possible nontrivial role of strong interactions in cosmological effects of new physics. In the [...] Read more.
The history of dark universe physics can be traced from processes in the very early universe to the modern dominance of dark matter and energy. Here, we review the possible nontrivial role of strong interactions in cosmological effects of new physics. In the case of ordinary QCD interaction, the existence of new stable colored particles such as new stable quarks leads to new exotic forms of matter, some of which can be candidates for dark matter. New QCD-like strong interactions lead to new stable composite candidates bound by QCD-like confinement. We put special emphasis on the effects of interaction between new stable hadrons and ordinary matter, formation of anomalous forms of cosmic rays and exotic forms of matter, like stable fractionally charged particles. The possible correlation of these effects with high energy neutrino and cosmic ray signatures opens the way to study new physics of strong interactions by its indirect multi-messenger astrophysical probes. Full article
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21 pages, 1464 KiB  
Article
Qualitative Analysis of the Dynamics of a Two-Component Chiral Cosmological Model
by Viktor Zhuravlev and Sergey Chervon
Universe 2020, 6(11), 195; https://doi.org/10.3390/universe6110195 - 24 Oct 2020
Cited by 6 | Viewed by 1704
Abstract
We present a qualitative analysis of chiral cosmological model (CCM) dynamics with two scalar fields in the spatially flat Friedman–Robertson–Walker Universe. The asymptotic behavior of chiral models is investigated based on the characteristics of the critical points of the selfinteraction potential and zeros [...] Read more.
We present a qualitative analysis of chiral cosmological model (CCM) dynamics with two scalar fields in the spatially flat Friedman–Robertson–Walker Universe. The asymptotic behavior of chiral models is investigated based on the characteristics of the critical points of the selfinteraction potential and zeros of the metric components of the chiral space. The classification of critical points of CCMs is proposed. The role of zeros of the metric components of the chiral space in the asymptotic dynamics is analysed. It is shown that such zeros lead to new critical points of the corresponding dynamical systems. Examples of models with different types of zeros of metric components are represented. Full article
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27 pages, 379 KiB  
Article
Making a Quantum Universe: Symmetry and Gravity
by Houri Ziaeepour
Universe 2020, 6(11), 194; https://doi.org/10.3390/universe6110194 - 23 Oct 2020
Cited by 7 | Viewed by 2088
Abstract
So far, none of attempts to quantize gravity has led to a satisfactory model that not only describe gravity in the realm of a quantum world, but also its relation to elementary particles and other fundamental forces. Here, we outline the preliminary results [...] Read more.
So far, none of attempts to quantize gravity has led to a satisfactory model that not only describe gravity in the realm of a quantum world, but also its relation to elementary particles and other fundamental forces. Here, we outline the preliminary results for a model of quantum universe, in which gravity is fundamentally and by construction quantic. The model is based on three well motivated assumptions with compelling observational and theoretical evidence: quantum mechanics is valid at all scales; quantum systems are described by their symmetries; universe has infinite independent degrees of freedom. The last assumption means that the Hilbert space of the Universe has SU(N)areapreservingDiff.(S2) symmetry, which is parameterized by two angular variables. We show that, in the absence of a background spacetime, this Universe is trivial and static. Nonetheless, quantum fluctuations break the symmetry and divide the Universe to subsystems. When a subsystem is singled out as reference—observer—and another as clock, two more continuous parameters arise, which can be interpreted as distance and time. We identify the classical spacetime with parameter space of the Hilbert space of the Universe. Therefore, its quantization is meaningless. In this view, the Einstein equation presents the projection of quantum dynamics in the Hilbert space into its parameter space. Finite dimensional symmetries of elementary particles emerge as a consequence of symmetry breaking when the Universe is divided to subsystems/particles, without having any implication for the infinite dimensional symmetry and its associated interaction-percived as gravity. This explains why gravity is a universal force. Full article
14 pages, 436 KiB  
Article
On a Crucial Role of Gravity in the Formation of Elementary Particles
by Ahmed Alharthy and Vladimir V. Kassandrov
Universe 2020, 6(11), 193; https://doi.org/10.3390/universe6110193 - 23 Oct 2020
Cited by 5 | Viewed by 4708
Abstract
We consider the model of minimally interacting electromagnetic, gravitational and massive scalar fields free of any additional nonlinearities. In the dimensionless form, the Lagranginan contains only one parameter γ=(mG/e)2 which corresponds to the ratio of [...] Read more.
We consider the model of minimally interacting electromagnetic, gravitational and massive scalar fields free of any additional nonlinearities. In the dimensionless form, the Lagranginan contains only one parameter γ=(mG/e)2 which corresponds to the ratio of gravitational and electromagnetic interactions and, for a typical elementary particle, is about 1040 in value. However, regular (soliton-like) solutions can exist only for γ0, so that gravity would be necessary to form the structure of an (extended) elementary particle. Unfortunately (in the stationary spherically symmetrical case), the numerical procedure breaks in the range γ0.9 so that whether the particle-like solutions actually exist in the model remains unclear. Nonetheless, for γ1 we obtain, making use of the minimal energy requirement, a discrete set of (horizon-free) electrically charged regular solutions of the Planck’s range mass and dimensions (“maximons”, “planckeons”, etc.). In the limit γ, the model reduces to the well-known coupled system of the Einstein and Klein–Gordon equations. We obtain—to our knowledge—for the first time, the discrete spectrum of neutral soliton-like solutions (“mini-boson stars”, “soliton stars”, etc.) Full article
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10 pages, 262 KiB  
Communication
Is the Axionic Dark Matter an Equilibrium System?
by Alexander B. Balakin and Amir F. Shakirzyanov
Universe 2020, 6(11), 192; https://doi.org/10.3390/universe6110192 - 22 Oct 2020
Cited by 15 | Viewed by 1442
Abstract
We consider an axionic dark matter model with a modified periodic potential for the pseudoscalar field in the framework of the axionic extension of the Einstein-aether theory. The modified potential is assumed to be equipped by the guiding function, which depends on the [...] Read more.
We consider an axionic dark matter model with a modified periodic potential for the pseudoscalar field in the framework of the axionic extension of the Einstein-aether theory. The modified potential is assumed to be equipped by the guiding function, which depends on the expansion scalar constructed as the trace of the covariant derivative of the aether velocity four-vector. The equilibrium state of the axion field is defined as the state, for which the modified potential itself and its first derivative with respect to the pseudoscalar field are equal to zero. We apply the developed formalism to the homogeneous isotropic cosmological model, and find the basic function, which describes the equilibrium state of the axionic dark matter in the expanding Universe. Full article
20 pages, 13075 KiB  
Article
Is OJ 287 a Single Supermassive Black Hole?
by Marina S. Butuzova and Alexander B. Pushkarev
Universe 2020, 6(11), 191; https://doi.org/10.3390/universe6110191 - 22 Oct 2020
Cited by 18 | Viewed by 2651
Abstract
Light curves for more than century optical photometric observations of the blazar OJ 287 reveals strong flares with a quasi-period of about 12 years. For a long time, this period has been interpreted by processes in a binary black hole system. We propose [...] Read more.
Light curves for more than century optical photometric observations of the blazar OJ 287 reveals strong flares with a quasi-period of about 12 years. For a long time, this period has been interpreted by processes in a binary black hole system. We propose an alternative explanation for this period, which is based on Doppler factor periodic variations of the emitting region caused by jet helicity. Using multi-epoch very large baseline interferometry (VLBI) observations carried out in a framework of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program and other VLBA (Very Long Baseline Array) archival experiments at the observing frequency of 15 GHz, we derived geometrical parameters of the jet helix. To reach an agreement between the VLBI and photometric optical observation data, the jet component motion at a small angle to the radial direction is necessary. Such non-radial motion is observed and, together with the jet helical shape, can be naturally explained by the development of the Kelvin–Helmholtz instability in the parsec-scale outflow. In this case, the true precession of the OJ 287 jet may manifest itself in differences between the peak flux values of the 12-year optical flares. A possibility to create this precession due to Lense–Thirring effect of a single supermassive black hole is also discussed. Full article
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