Special Issue "Selected Papers from the 1st International Electronic Conference on Universe (ECU 2021)"

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (30 June 2021).

Special Issue Editors

Prof. Dr. James A. Isenberg
E-Mail Website
Guest Editor
Department of Mathematics, Fenton Hall, University of Oregon, Eugene, OR 97403-1222, USA
Interests: Mathematical Relativity; Geometric Heat Flow; Nonlinear Wave Equations; Momentum maps and classical field theory
Prof. Dr. Gerald B. Cleaver
E-Mail Website
Guest Editor
Department of Physics and Center for Astrophysics, Space Physics, Baylor University, Waco, TX 76798-7316, USA
Interests: quantum field theory; quantum gravity; quantum cosmology; traversable wormholes; Casimir effect; quantum information theory; quantum thermodynamics; philosophical foundations of quantum mechanics; multiverse concepts especially related scientific and philosophical aspects
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Lijing Shao
E-Mail Website
Guest Editor
Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100080, China
Interests: Tests of gravity theories; Gravitational waves; Pulsars and neutron stars; Astrophysical studies of dark matter; Black hole spacetime; Precision tests of fundamental physics; Bayesian data analysis and statistics
Prof. Dr. Gonzalo J. Olmo
E-Mail Website
Guest Editor
Department of Theoretical Physics & IFIC – University of Valencia & CSIC, C/ Dr. Moliner 50, Burjassot 46100, Valencia, Spain
Interests: black holes; singularities; quantum fields in curved space-time; inflation; modified gravity; Palatini formalism; stellar structure models; compact objects
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Giacomo Tommei
E-Mail Website
Guest Editor
Department of Mathematics University of Pisa, 56126 Pisa, Italy
Interests: Celestial Mechanics; space debris; Orbit determination of NEOs; Radio science experiments

Special Issue Information

Dear Colleagues,

1st International Electronic Conference on Universe (ECU 2021) will be held held from 22 to 28 February, 2021 (https://sciforum.net/conference/ECU2021), verifying the great interest of the related community in this Conference Series. The e-conference was hosted on sciforum.net, an online platform developed by MDPI for scholarly exchange and collaboration.

During the event, a large number of excellent contributions covering key areas of opportunity and challenge in related area will be presented. More specifically, the following areas will be covered:

  • General relativity and gravitation;
  • Quantum field theories;
  • Black Holes, Worm Holes, and Warped Spacetimes
  • Trans-Planckian Theories
  • Quantum Gravity Theories
  • Dark matter and dark energy;
  • High energy physics;
  • Compact objects;
  • Deep-space probes.

This Special Issue welcomes selected papers from ECU 2021 that promote and advance the exciting and rapidly changing.

Submitted contributions will be subjected to peer review and—upon acceptance—will be published with the aim of rapidly and widely disseminating research results, developments, and applications.

It should be noted that submitted manuscripts should have at least 30% additional, new, and unpublished material compared to the ECU 2021 published paper.

We look forward to receiving your contributions.

Prof. Dr. James A. Isenberg
Prof. Dr. Gerald B. Cleaver
Dr. Lijing Shao
Prof. Dr. Gonzalo J. Olmo
Prof. Giacomo Tommei
Guest Editors

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 papers will be 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. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. 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.

Published Papers (26 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Article
Does the Loop Quantum μo Scheme Permit Black Hole Formation?
by and
Universe 2021, 7(11), 406; https://doi.org/10.3390/universe7110406 (registering DOI) - 28 Oct 2021
Abstract
We explore the way different loop quantization prescriptions affect the formation of trapped surfaces in the gravitational collapse of a homogeneous dust cloud, with particular emphasis on the so-called μo scheme in which loop quantum cosmology was initially formulated. Its undesirable features [...] Read more.
We explore the way different loop quantization prescriptions affect the formation of trapped surfaces in the gravitational collapse of a homogeneous dust cloud, with particular emphasis on the so-called μo scheme in which loop quantum cosmology was initially formulated. Its undesirable features in cosmological models led to the so-called improved dynamics or the μ¯ scheme. While the jury is still out on the right scheme for black hole spacetimes, we show that as far as black hole formation is concerned, the μo scheme has another, so far unknown, serious problem. We found that in the μo scheme, no trapped surfaces would form for a nonsingular collapse of a homogeneous dust cloud in the marginally bound case unless the minimum nonzero area of the loops over which holonomies are computed or the Barbero–Immirzi parameter decreases almost four times from its standard value. It turns out that the trapped surfaces in the μo scheme for the marginally bound case are also forbidden for an arbitrary matter content as long as the collapsing interior is isometric to a spatially flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime. We found that in contrast to the situation in the μo scheme, black holes can form in the μ¯ scheme, as well as other lattice refinements with a mass gap determined by quantum geometry. Full article
Show Figures

Figure 1

Article
Cold Dark Matter: A Gluonic Bose–Einstein Condensate in Anti-de Sitter Space Time
Universe 2021, 7(11), 402; https://doi.org/10.3390/universe7110402 - 25 Oct 2021
Viewed by 366
Abstract
In the same way as the realization of some of the famous gedanken experiments imagined by the founding fathers of quantum mechanics has recently led to the current renewal of the interpretation of quantum physics, it seems that the most recent progress of [...] Read more.
In the same way as the realization of some of the famous gedanken experiments imagined by the founding fathers of quantum mechanics has recently led to the current renewal of the interpretation of quantum physics, it seems that the most recent progress of observational astrophysics can be interpreted as the realization of some cosmological gedanken experiments such as the removal from the universe of the whole visible matter or the cosmic time travel leading to a new cosmological standard model. This standard model involves two dark components of the universe, dark energy and dark matter. Whereas dark energy is usually associated with the cosmological constant, we propose explaining dark matter as a pure QCD effect, namely a gluonic Bose–Einstein condensate, following the transition from the quark gluon plasma phase to the colorless hadronic phase. Our approach not only allows us to assume a Dark/Visible ratio equal to 11/2 but also provides gluons (and di-gluons, viewed as quasi-particles) with an extra mass of vibrational nature. Such an interpretation would support the idea that, apart from the violation of the matter/antimatter symmetry satisfying the Sakharov’s conditions, the reconciliation of particle physics and cosmology needs not the recourse to any ad hoc fields, particles or hidden variables. Full article
Article
Baryon-Antibaryon Annihilation in the Evolution of Antimatter Domains in Baryon-Asymmetric Universe
Universe 2021, 7(9), 347; https://doi.org/10.3390/universe7090347 - 15 Sep 2021
Viewed by 472
Abstract
Non-trivial baryosynthesis scenarios can lead to the existence of antimatter domains in a baryon-asymmetrical Universe. The consequences of antibaryon-baryon annihilation at the border of antimatter domains is investigated. Low-density antimatter domains are further classified according to the boundary interactions. A similar classification scheme [...] Read more.
Non-trivial baryosynthesis scenarios can lead to the existence of antimatter domains in a baryon-asymmetrical Universe. The consequences of antibaryon-baryon annihilation at the border of antimatter domains is investigated. Low-density antimatter domains are further classified according to the boundary interactions. A similar classification scheme is also proposed for higher-densities antimatter domains. The antiproton-proton annihilation interactions are therefore schematized and evaluated. The antinuclei-nuclei-interaction patterns are investigated. The two-point correlation functions for antimatter domains are studied in the case of baryon-antibaryon boundary interactions, which influence the space and time evolution. The space-time evolution of antimatter domains after the photon thermalization epoch is analyzed. Full article
Article
FLRW Cosmological Models with Dynamic Cosmological Term in Modified Gravity
Universe 2021, 7(9), 319; https://doi.org/10.3390/universe7090319 - 28 Aug 2021
Viewed by 374
Abstract
Although the standard lambda cold dark matter cosmological model is quite successful in describing the universe, there are still several issues that are still not resolved. Some of these are the cosmological constant problem, certain anomalies in the cosmic microwave background radiation and [...] Read more.
Although the standard lambda cold dark matter cosmological model is quite successful in describing the universe, there are still several issues that are still not resolved. Some of these are the cosmological constant problem, certain anomalies in the cosmic microwave background radiation and whether general relativity is valid on large scales. Therefore, it is interesting to examine modified theories in an attempt to solve these problems, and to examine the entire range of possibilities that are allowed. In this work, we examine one of these modified theories, viz., f(R,T) gravity. We study the homogeneous and isotropic models in this theory, which have some pleasing features, such as no initial singularity, a dynamic cosmological term, and a transition from early deceleration to late-time acceleration as intimated by observations. The physical parameters of the model, as well as the energy conditions, are discussed and a viable cosmological model can be constructed. Full article
Show Figures

Figure 1

Article
The Hubble Tension, the M Crisis of Late Time H(z) Deformation Models and the Reconstruction of Quintessence Lagrangians
Universe 2021, 7(8), 300; https://doi.org/10.3390/universe7080300 - 13 Aug 2021
Cited by 2 | Viewed by 404
Abstract
We present a detailed and pedagogical analysis of recent cosmological data, including CMB, BAO, SnIa and the recent local measurement of H0. We thus obtain constraints on the parameters of these standard dark energy parameterizations, including ΛCDM, [...] Read more.
We present a detailed and pedagogical analysis of recent cosmological data, including CMB, BAO, SnIa and the recent local measurement of H0. We thus obtain constraints on the parameters of these standard dark energy parameterizations, including ΛCDM, and H(z) deformation models such as wCDM (constant equation of state w of dark energy), and the CPL model (corresponding to the evolving dark energy equation-of-state parameter w(z)=w0+waz1+z). The fitted parameters include the dark matter density Ω0m, the SnIa absolute magnitude M, the Hubble constant H0 and the dark energy parameters (e.g., w for wCDM). All models considered lead to a best-fit value of M that is inconsistent with the locally determined value obtained by Cepheid calibrators (M tension). We then use the best-fit dark energy parameters to reconstruct the quintessence Lagrangian that would be able to reproduce these best-fit parameterizations. Due to the derived late phantom behavior of the best-fit dark energy equation-of-state parameter w(z), the reconstructed quintessence models have a negative kinetic term and are therefore plagued with instabilities. Full article
Show Figures

Figure 1

Article
Balancing Asymmetric Dark Matter with Baryon Asymmetry and Dilution of Frozen Dark Matter by Sphaleron Transition
Universe 2021, 7(8), 275; https://doi.org/10.3390/universe7080275 - 30 Jul 2021
Viewed by 641
Abstract
In this paper, we study the effect of electroweak sphaleron transition and electroweak phase transition (EWPT) in balancing the baryon excess and the excess stable quarks of the 4th generation. Sphaleron transitions between baryons, leptons and the 4th family of leptons and quarks [...] Read more.
In this paper, we study the effect of electroweak sphaleron transition and electroweak phase transition (EWPT) in balancing the baryon excess and the excess stable quarks of the 4th generation. Sphaleron transitions between baryons, leptons and the 4th family of leptons and quarks establish a definite relationship between the value and sign of the 4th family excess and baryon asymmetry. This relationship provides an excess of stable U¯ antiquarks, forming dark atoms—the bound state of (U¯U¯U¯) the anti-quark cluster and primordial helium nucleus. If EWPT is of the second order and the mass of U quark is about 3.5 TeV, then dark atoms can explain the observed dark matter density. In passing by, we show the small, yet negligible dilution in the pre-existing dark matter density, due to the sphaleron transition. Full article
Show Figures

Figure 1

Article
Anisotropic Cosmological Model in a Modified Theory of Gravitation
Universe 2021, 7(7), 226; https://doi.org/10.3390/universe7070226 - 04 Jul 2021
Cited by 1 | Viewed by 511
Abstract
Current observations indicate that, on a large enough scale, the universe is homogeneous and isotropic. However, this does not preclude the possibility of some anisotropy having occurred during the early stages of the evolution of the universe, which could then have been damped [...] Read more.
Current observations indicate that, on a large enough scale, the universe is homogeneous and isotropic. However, this does not preclude the possibility of some anisotropy having occurred during the early stages of the evolution of the universe, which could then have been damped out later. This idea has aroused interest in the Bianchi models, which are homogeneous but anisotropic. Secondly, there is much interest in modified gravity these days due to the problems that the usual ΛCDM model faces in general relativity. Hence, in this paper, a study was conducted on the Bianchi type-I cosmological model in f(R,T)-modified gravity. Following some ideas from cosmography, a specific form of the deceleration parameter was assumed, leading to a model that exhibited a transition from early deceleration to late-time acceleration. The derived model approached isotropy at late times. The physical properties of the model were discussed, and expressions for the various parameters of the model were derived. It is also possible to make progress towards solving the cosmological constant problem, since in this model in f(R,T) gravity, a variable cosmological-type parameter arose, which was large early on but decreased to a constant value in later times. Full article
Article
Multimessenger Probes for New Physics in Light of A. Sakharov’s Legacy in Cosmoparticle Physics
Universe 2021, 7(7), 222; https://doi.org/10.3390/universe7070222 - 02 Jul 2021
Viewed by 403
Abstract
A.D. Sakharov’s legacy in now standard model of the Universe is not reduced to baryosynthesis but extends to the foundation of cosmoparticle physics, which studies the fundamental relationship of cosmology and particle physics. Development of cosmoparticle physics involves cross-disciplinary physical, astrophysical and cosmological [...] Read more.
A.D. Sakharov’s legacy in now standard model of the Universe is not reduced to baryosynthesis but extends to the foundation of cosmoparticle physics, which studies the fundamental relationship of cosmology and particle physics. Development of cosmoparticle physics involves cross-disciplinary physical, astrophysical and cosmological studies of physics Beyond the Standard model (BSM) of elementary particles. To probe physical models for inflation, baryosynthesis and dark matter cosmoparticle physics pays special attention to model dependent messengers of the corresponding models, making their tests possible. Positive evidence for such exotic phenomena as nuclear interacting dark atoms, primordial black holes or antimatter globular cluster in our galaxy would provide the selection of viable BSM models determination of their parameters. Full article
Show Figures

Figure 1

Article
Effects of Higher Order Retarded Gravity
Universe 2021, 7(7), 207; https://doi.org/10.3390/universe7070207 - 23 Jun 2021
Viewed by 357
Abstract
In a recent paper, we have a shown that the flattening of galactic rotation curves can be explained by retardation. However, this will rely on a temporal change of galactic mass. In our previous work, we kept only second order terms of the [...] Read more.
In a recent paper, we have a shown that the flattening of galactic rotation curves can be explained by retardation. However, this will rely on a temporal change of galactic mass. In our previous work, we kept only second order terms of the retardation time in our analysis, while higher terms in the Taylor expansion where not considered. Here we consider analysis to all orders and show that a second order analysis will indeed suffice, and higher order terms can be neglected. Full article
Show Figures

Figure 1

Article
Testing Gravitational Theories in the Field of the Earth with the SaToR-G Experiment
Universe 2021, 7(6), 192; https://doi.org/10.3390/universe7060192 - 08 Jun 2021
Viewed by 483
Abstract
A new satellite-based experiment in the field of gravitation, SaToR-G, is presented. It aims to compare the predictions of different theories of gravitation in the limit of weak-field and slow-motion. The ultimate goal of SaToR-G is searching for possible “new physics” beyond General [...] Read more.
A new satellite-based experiment in the field of gravitation, SaToR-G, is presented. It aims to compare the predictions of different theories of gravitation in the limit of weak-field and slow-motion. The ultimate goal of SaToR-G is searching for possible “new physics” beyond General Relativity, which represent the state-of-the-art of our current knowledge of gravitational physics. A key role in the above perspective is the theoretical and experimental framework that confines our work. To this end, we will exploit as much as possible the classical framework suggested by R.H. Dicke over fifty years ago. Full article
Article
On the Coupling of Generalized Proca Fields to Degenerate Scalar-Tensor Theories
Universe 2021, 7(6), 190; https://doi.org/10.3390/universe7060190 - 07 Jun 2021
Cited by 1 | Viewed by 226
Abstract
We prove that vector fields described by the generalized Proca class of theories do not admit consistent coupling with a gravitational sector defined by a scalar–tensor theory of the degenerate type. Under the assumption that there exists a frame in which the Proca [...] Read more.
We prove that vector fields described by the generalized Proca class of theories do not admit consistent coupling with a gravitational sector defined by a scalar–tensor theory of the degenerate type. Under the assumption that there exists a frame in which the Proca field interacts with gravity only through the metric tensor, our analysis shows that at least one of the constraints associated with the degeneracy of the scalar–tensor sector is inevitably lost whenever the vector theory includes coupling with the Christoffel connection. Full article
Article
New Black Hole Solutions in N = 2 and N = 8 Gauged Supergravity
Universe 2021, 7(6), 187; https://doi.org/10.3390/universe7060187 - 06 Jun 2021
Cited by 1 | Viewed by 568
Abstract
We review a special class of N=2 supergravity model that interpolates all the single-dilaton truncations of the maximal SO(8) gauged supergravity. We also provide explicit non-extremal, charged black hole solutions and their supersymmetric limits, asymptotic charges, thermodynamics and [...] Read more.
We review a special class of N=2 supergravity model that interpolates all the single-dilaton truncations of the maximal SO(8) gauged supergravity. We also provide explicit non-extremal, charged black hole solutions and their supersymmetric limits, asymptotic charges, thermodynamics and boundary conditions. We also discuss a suitable Hamilton–Jacobi formulation and related BPS flow equations for the supersymmetric configurations, with an explicit form for the superpotential function. Finally, we briefly analyze certain models within the class under consideration as consistent truncations of the maximal, N=8 gauged supergravity in four dimensions. Full article
Show Figures

Figure 1

Article
Introducing Quantum and Statistical Physics in the Footsteps of Einstein: A Proposal
Universe 2021, 7(6), 184; https://doi.org/10.3390/universe7060184 - 04 Jun 2021
Viewed by 531
Abstract
Introducing some fundamental concepts of quantum physics to high school students, and to their teachers, is a timely challenge. In this paper we describe ongoing research, in which a teaching–learning sequence for teaching quantum physics, whose inspiration comes from some of the fundamental [...] Read more.
Introducing some fundamental concepts of quantum physics to high school students, and to their teachers, is a timely challenge. In this paper we describe ongoing research, in which a teaching–learning sequence for teaching quantum physics, whose inspiration comes from some of the fundamental papers about the quantum theory of radiation by Albert Einstein, is being developed. The reason for this choice goes back essentially to the fact that the roots of many subtle physical concepts, namely quanta, wave–particle duality and probability, were introduced for the first time in one of these papers, hence their study may represent a useful intermediate step towards tackling the final incarnation of these concepts in the full theory of quantum mechanics. An extended discussion of some elementary tools of statistical physics, mainly Boltzmann’s formula for entropy and statistical distributions, which are necessary but may be unfamiliar to the students, is included. This discussion can also be used independently to introduce some rudiments of statistical physics. In this case, part of the inspiration came from some of Einstein’s papers. We present preliminary, qualitative results obtained with both teachers and selected pupils from various high schools in southern Italy, in the course of several outreach activities. Although the proposal was only tested in this limited context for now, the preliminary results are very promising and they indicate that this proposal can be fruitfully employed for the task. Full article
Communication
Beryllium Radioactive Isotopes as a Probe to Measure the Residence Time of Cosmic Rays in the Galaxy and Halo Thickness: A “Data-Driven” Approach
Universe 2021, 7(6), 183; https://doi.org/10.3390/universe7060183 - 04 Jun 2021
Viewed by 527
Abstract
Cosmic rays are a powerful tool for the investigation of the structure of the magnetic fields in the Galactic halo and the properties of the inter-stellar medium. Two parameters of the cosmic ray propagation models, the Galactic halo (half) thickness, H, and [...] Read more.
Cosmic rays are a powerful tool for the investigation of the structure of the magnetic fields in the Galactic halo and the properties of the inter-stellar medium. Two parameters of the cosmic ray propagation models, the Galactic halo (half) thickness, H, and the diffusion coefficient, D, are loosely constrained by current cosmic ray flux measurements; in particular, a large degeneracy exists, with only H/D being well measured. The 10Be/9Be isotopic flux ratio (thanks to the 2 My lifetime of 10Be) can be used as a radioactive clock providing the measurement of cosmic ray residence time in a galaxy. This is an important probe with which to solve the H/D degeneracy. Past measurements of 10Be/9Be isotopic flux ratios in cosmic rays are scarce, and were limited to low energy and affected by large uncertainties. Here a new technique to measure 10Be/9Be isotopic flux ratio, with a data-driven approach in magnetic spectrometers is presented. As an example, by applying the method to beryllium events published via PAMELA experiment, it is now possible to determine the important 10Be/9Be measurement while avoiding the prohibitive uncertainties coming from Monte Carlo simulations. It is shown how the accuracy of PAMELA data strengthens the experimental indication for the relativistic time dilation of 10Be decay in cosmic rays; this should improve the knowledge of the H parameter. Full article
Show Figures

Figure 1

Article
Teaching Science in Today’s Society: The Case of Particle Physics for Primary Schools
Universe 2021, 7(6), 169; https://doi.org/10.3390/universe7060169 - 30 May 2021
Viewed by 708
Abstract
The rapid changes in science and technology witnessed in recent decades have significantly contributed to the arousal of the awareness by decision-makers and the public as a whole of the need to strengthen the connection between outreach activities of universities and research institutes [...] Read more.
The rapid changes in science and technology witnessed in recent decades have significantly contributed to the arousal of the awareness by decision-makers and the public as a whole of the need to strengthen the connection between outreach activities of universities and research institutes and the activities of educational institutions, with a central role played by schools. While the relevance of the problem is nowadays unquestioned, no unique and fully satisfactory solution has been identified. In the present paper we would like to contribute to the discussion on the subject by reporting on an ongoing project aimed to teach Particle Physics in primary schools. We will start from the past and currently planned activities in this project in order to establish a broader framework to describe the conditions for the fruitful interplay between researchers and teachers. We will also emphasize some aspects related to the dissemination of outreach materials by research institutions, in order to promote the access and distribution of scientific information in a way suited to the different age of the target students. Full article
Article
Decoupled Embedding Class-One Strange Stars in Self-Interacting Brans–Dicke Gravity
Universe 2021, 7(6), 161; https://doi.org/10.3390/universe7060161 - 24 May 2021
Cited by 2 | Viewed by 366
Abstract
This work aims to extend two isotropic solutions to the anisotropic domain by decoupling the field equations in self-interacting Brans–Dicke theory. The extended solutions are obtained by incorporating an additional source in the isotropic fluid distribution. We deform the radial metric potential to [...] Read more.
This work aims to extend two isotropic solutions to the anisotropic domain by decoupling the field equations in self-interacting Brans–Dicke theory. The extended solutions are obtained by incorporating an additional source in the isotropic fluid distribution. We deform the radial metric potential to disintegrate the system of field equations into two sets such that each set corresponds to only one source (either isotropic or additional). The system related to the anisotropic source is solved by employing the MIT bag model as an equation of state. Further, we develop two isotropic solutions by plugging well-behaved radial metric potentials in Karmarkar’s embedding condition. The junction conditions at the surface of the star are imposed to specify the unknown constants appearing in the solution. We examine different physical characteristics of the constructed quark star models by using the mass and radius of PSR J1903+327. It is concluded that, in the presence of a massive scalar field, both stellar structures are well-behaved, viable and stable for smaller values of the decoupling parameter. Full article
Show Figures

Figure 1

Article
Moon Mapping Project Results on Solar Wind Ion Flux and Composition
Universe 2021, 7(5), 157; https://doi.org/10.3390/universe7050157 - 19 May 2021
Viewed by 525
Abstract
The “Moon Mapping” project is a collaboration between the Italian and Chinese Governments allowing cooperation and exchange between students from both countries. The main aim of the project is to analyze remotely-sensed data collected by the Chinese space missions Chang’E-1/2 over the Moon [...] Read more.
The “Moon Mapping” project is a collaboration between the Italian and Chinese Governments allowing cooperation and exchange between students from both countries. The main aim of the project is to analyze remotely-sensed data collected by the Chinese space missions Chang’E-1/2 over the Moon surface. The Italian Space Agency is responsible for the Italian side and the Center of Space Exploration, while the China Ministry of Education is responsible for the Chinese side. In this article, we summarize the results of the “Moon Mappining” project topic #1: “map of the solar wind ion” using the data collected by Chang’E-1 satellite. Chang’E-1 is a lunar orbiter, its revolution period lasts 2 h, and its orbit is polar. The satellite is equipped with two Solar Wind Ion Detectors (SWIDs) that are two perpendicular electrostatic spectrometers mapping the sky with a field of view of 15° × 6.7° × 24 ch. The spectrometers can measure solar wind flux in the range 40 eV/q–17 keV/q with an energy resolution of 8% and time resolution of ∼3 s. The data collected by the two Solar Wind Ion Detectors are analyzed to characterize the solar wind flux and composition on the Moon surface and to study the time variations due to the solar activity. The data measured by Chang’E-1 compared with the one measured in the same period by the electrostatic spectrometers onboard the ACE satellite, or with another solar activity indicator as the sunspot number, enrich the multi-messenger/multi-particle view of the Sun, gathering valuable information about the space weather outside the Earth magnetosphere. Full article
Show Figures

Figure 1

Article
Dynamical Analysis of Charged Dissipative Cylindrical Collapse in Energy-Momentum Squared Gravity
Universe 2021, 7(5), 154; https://doi.org/10.3390/universe7050154 - 18 May 2021
Cited by 1 | Viewed by 332
Abstract
This paper investigates the dynamics of charged cylindrical collapse with the dissipative matter configuration in f(R,TαβTαβ) theory. This newly formulated theory resolves the primordial singularity and provides feasible cosmological results in the early [...] Read more.
This paper investigates the dynamics of charged cylindrical collapse with the dissipative matter configuration in f(R,TαβTαβ) theory. This newly formulated theory resolves the primordial singularity and provides feasible cosmological results in the early universe.Moreover, its implications occur in high curvature regime where the deviations of energy-momentum squared gravity from general relativity is confirmed. We establish dynamical and transport equations through the Misner–Sharp and Mu¨ler–Israel Stewart techniques, respectively. We then couple these equations to examine the impact of effective fluid parameters and correction terms on the collapsing phenomenon. A connection between the modified terms, matter parameters, and Weyl tensor is also developed. To obtain conformal flatness, we choose a particular model of this theory and assume that dust matter with zero charge leads to conformal flatness and homogenous energy density. We found that the modified terms, dissipative matter, and electromagnetic field reduce the collapsing phenomenon. Full article
Article
On A. D. Sakharov’s Hypothesis of Cosmological Transitions with Changes in the Signature of the Metric
Universe 2021, 7(5), 151; https://doi.org/10.3390/universe7050151 - 17 May 2021
Viewed by 664
Abstract
The paper discusses possible consequences of A. D. Sakharov’s hypothesis of cosmological transitions with changes in the signature of the metric, based on the path integral approach. This hypothesis raises a number of mathematical and philosophical questions. Mathematical questions concern the definition of [...] Read more.
The paper discusses possible consequences of A. D. Sakharov’s hypothesis of cosmological transitions with changes in the signature of the metric, based on the path integral approach. This hypothesis raises a number of mathematical and philosophical questions. Mathematical questions concern the definition of the path integral to include integration over spacetime regions with different signatures of the metric. One possible way to describe the changes in the signature is to admit time and space coordinates to be purely imaginary. It may look like a generalization of what we have in the case of pseudo-Riemannian manifolds with a non-trivial topology. The signature in these regions can be fixed by special gauge conditions on components of the metric tensor. The problem is what boundary conditions should be imposed on the boundaries of these regions and how they should be taken into account in the definition of the path integral. The philosophical question is what distinguishes the time coordinate among other coordinates but the sign of the corresponding principal value of the metric tensor. In particular, there is an attempt in speculating how the existence of the regions with different signature can affect the evolution of the Universe. Full article
Show Figures

Figure 1

Article
De Sitter Solutions in Einstein–Gauss–Bonnet Gravity
Universe 2021, 7(5), 149; https://doi.org/10.3390/universe7050149 - 16 May 2021
Cited by 5 | Viewed by 448
Abstract
De Sitter solutions play an important role in cosmology because the knowledge of unstable de Sitter solutions can be useful to describe inflation, whereas stable de Sitter solutions are often used in models of late-time acceleration of the Universe. The Einstein–Gauss–Bonnet gravity cosmological [...] Read more.
De Sitter solutions play an important role in cosmology because the knowledge of unstable de Sitter solutions can be useful to describe inflation, whereas stable de Sitter solutions are often used in models of late-time acceleration of the Universe. The Einstein–Gauss–Bonnet gravity cosmological models are actively used both as inflationary models and as dark energy models. To modify the Einstein equations one can add a nonlinear function of the Gauss–Bonnet term or a function of the scalar field multiplied on the Gauss–Bonnet term. The effective potential method essentially simplifies the search and stability analysis of de Sitter solutions, because the stable de Sitter solutions correspond to minima of the effective potential. Full article
Show Figures

Figure 1

Article
The Dirac Sea, T and C Symmetry Breaking, and the Spinor Vacuum of the Universe
Universe 2021, 7(5), 124; https://doi.org/10.3390/universe7050124 - 01 May 2021
Viewed by 372
Abstract
We have developed a quantum field theory of spinors based on the algebra of canonical anticommutation relations (CAR algebra) of Grassmann densities in the momentum space. We have proven the existence of two spinor vacua. Operators C and T transform the normal vacuum [...] Read more.
We have developed a quantum field theory of spinors based on the algebra of canonical anticommutation relations (CAR algebra) of Grassmann densities in the momentum space. We have proven the existence of two spinor vacua. Operators C and T transform the normal vacuum into an alternative one, which leads to the breaking of the C and T symmetries. The CPT is the real structure operator; it preserves the normal vacuum. We have proven that, in the theory of the Dirac Sea, the formula for the charge conjugation operator must contain an additional generalized Dirac conjugation operator. Full article
Article
Multi-Field versus Single-Field in the Supergravity Models of Inflation and Primordial Black Holes
Universe 2021, 7(5), 115; https://doi.org/10.3390/universe7050115 - 21 Apr 2021
Cited by 4 | Viewed by 535
Abstract
We review the models unifying inflation and Primordial Black Hole (PBH) formation, which are based on the modified (Starobinsky-type) supergravity. We begin with the basic (Starobinsky) inflationary model of modified gravity and its alpha-attractor-type generalizations for PBH production, and recall how all those [...] Read more.
We review the models unifying inflation and Primordial Black Hole (PBH) formation, which are based on the modified (Starobinsky-type) supergravity. We begin with the basic (Starobinsky) inflationary model of modified gravity and its alpha-attractor-type generalizations for PBH production, and recall how all those single-field models can be embedded into the minimal supergravity. Then, we focus on the effective two-field models arising from the modified (Starobinsky-type) supergravity and compare them to the single-field models under review. Those two-field models describe double inflation whose first stage is driven by Starobinsky’s scalaron and whose second stage is driven by another scalar belonging to the supergravity multiplet. The power spectra are numerically computed, and it is found that the ultra-slow-roll regime gives rise to the enhancement (peak) in the scalar power spectrum leading to an efficient PBH formation. The resulting PBH masses and their density fraction (as part of dark matter) are found to be in agreement with cosmological observations. The PBH-induced gravitational waves, if any, are shown to be detectable by the ground-based and space-based gravitational interferometers under construction. Full article
Show Figures

Figure 1

Article
Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle
Universe 2021, 7(4), 107; https://doi.org/10.3390/universe7040107 - 20 Apr 2021
Cited by 3 | Viewed by 366
Abstract
According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would [...] Read more.
According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s1 along l=264,b=48. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology. Full article
Show Figures

Figure 1

Article
Gravitational Interaction in the Chimney Lattice Universe
Universe 2021, 7(4), 101; https://doi.org/10.3390/universe7040101 - 15 Apr 2021
Viewed by 430
Abstract
We investigate the influence of the chimney topology T×T×R of the Universe on the gravitational potential and force that are generated by point-like massive bodies. We obtain three distinct expressions for the solutions. One follows from Fourier expansion of [...] Read more.
We investigate the influence of the chimney topology T×T×R of the Universe on the gravitational potential and force that are generated by point-like massive bodies. We obtain three distinct expressions for the solutions. One follows from Fourier expansion of delta functions into series using periodicity in two toroidal dimensions. The second one is the summation of solutions of the Helmholtz equation, for a source mass and its infinitely many images, which are in the form of Yukawa potentials. The third alternative solution for the potential is formulated via the Ewald sums method applied to Yukawa-type potentials. We show that, for the present Universe, the formulas involving plain summation of Yukawa potentials are preferable for computational purposes, as they require a smaller number of terms in the series to reach adequate precision. Full article
Show Figures

Figure 1

Article
Quantum Physics Literacy Aimed at K12 and the General Public
Universe 2021, 7(4), 86; https://doi.org/10.3390/universe7040086 - 01 Apr 2021
Viewed by 650
Abstract
Educating K12 students and general public in quantum physics represents an evitable must no longer since quantum technologies are going to revolutionize our lives. Quantum literacy is a formidable challenge and an extraordinary opportunity for a massive cultural uplift, where citizens learn how [...] Read more.
Educating K12 students and general public in quantum physics represents an evitable must no longer since quantum technologies are going to revolutionize our lives. Quantum literacy is a formidable challenge and an extraordinary opportunity for a massive cultural uplift, where citizens learn how to engender creativity and practice a new way of thinking, essential for smart community building. Scientific thinking hinges on analyzing facts and creating understanding, and it is then formulated with the dense mathematical language for later fact checking. Within classical physics, learners’ intuition may in principle be educated via classroom demonstrations of everyday-life phenomena. Their understanding can even be framed with the mathematics suited to their instruction degree. For quantum physics, on the contrary, we have no experience of quantum phenomena and the required mathematics is beyond non-expert reach. Therefore, educating intuition needs imagination. Without rooting to experiments and some degree of formal framing, educators face the risk to provide only evanescent tales, often misled, while resorting to familiar analogies. Here, we report on the realization of QPlayLearn, an online platform conceived to explicitly address challenges and opportunities of massive quantum literacy. QPlayLearn’s mission is to provide multilevel education on quantum science and technologies to anyone, regardless of age and background. To this aim, innovative interactive tools enhance the learning process effectiveness, fun, and accessibility, while remaining grounded on scientific correctness. Examples are games for basic quantum physics teaching, on-purpose designed animations, and easy-to-understand explanations on terminology and concepts by global experts. As a strategy for massive cultural change, QPlayLearn offers diversified content for different target groups, from primary school all the way to university physics students. It is addressed also to companies wishing to understand the potential of the emergent quantum industry, journalists, and policymakers needing to seize what quantum technologies are about, as well as all quantum science enthusiasts. Full article
Show Figures

Figure 1

Article
Nonperturbative Quantization Approach for QED on the Hopf Bundle
Universe 2021, 7(3), 65; https://doi.org/10.3390/universe7030065 - 11 Mar 2021
Viewed by 431
Abstract
We consider the Dirac equation and Maxwell’s electrodynamics in R×S3 spacetime, where a three-dimensional sphere is the Hopf bundle S3S2. In both cases, discrete spectra of classical solutions are obtained. Based on the solutions obtained, [...] Read more.
We consider the Dirac equation and Maxwell’s electrodynamics in R×S3 spacetime, where a three-dimensional sphere is the Hopf bundle S3S2. In both cases, discrete spectra of classical solutions are obtained. Based on the solutions obtained, the quantization of free, noninteracting Dirac and Maxwell fields is carried out. The method of nonperturbative quantization of interacting Dirac and Maxwell fields is suggested. The corresponding operator equations and the infinite set of the Schwinger–Dyson equations for Green’s functions is written down. We write a simplified set of equations describing some physical situations to illustrate the suggested scheme of nonperturbative quantization. Additionally, we discuss the properties of quantum states and operators of interacting fields. Full article
Show Figures

Figure 1

Back to TopTop