Selected Papers from the 2nd International Electronic Conference on Universe (ECU 2023)

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

Deadline for manuscript submissions: closed (30 June 2023) | Viewed by 9879

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Department of Mathematics, University of Pisa, 56127 Pisa, Italy
Interests: celestial mechanics; space debris; orbit determination of NEOs; radio science experiments
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Early Universe Cosmology and Strings (EUCOS) Group, Center for Astrophysics, Space Physics and Engineering Research (CASPER), Baylor University, Waco, TX 76798, 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 those related the sciences and philosophy
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Department of Physics (Interuniversity), University of Bari Aldo Moro, 70121 Bari, Italy
Interests: particle detectors; nuclear and subnuclear physics; astroparticle physics
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Associate Professor, Department of Theoretical Physics & IFIC, University of Valencia & CSIC, C/ Dr. Moliner 50, 46100 Burjassot, Valencia, Spain
Interests: black holes; singularities; quantum fields in curved space-time; inflation; modified gravity; Palatini formalism; stellar structure models; compact objects
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Special Issue Information

Dear Colleagues,

The 2nd International Electronic Conference on Universe (ECU 2023) will be held from 16 February to 2 March, 2023 (https://ecu2023.sciforum.net/), aiming to bring together the Universe scientific community. The e-conference will be hosted on sciforum.net, an online platform developed by MDPI to facilitate scholarly exchange and collaboration.

Several excellent contributions covering key areas of opportunity and challenge in related areas will be presented at the conference, including on the following topics:

  • Gravitation and cosmology;
  • Field theory;
  • High-energy nuclear and particle physics;
  • Foundations of quantum mechanics and quantum gravity;
  • Space and planetary sciences;
  • Galaxies and clusters;
  • Compact objects;
  • Stellar and solar physics;
  • Women scientists in astronomy, astrophysics and cosmology.

This Special Issue welcomes selected papers from ECU 2023 that promote and advance new knowledge in this exciting and rapidly changing field.

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

Submitted manuscripts should have at least 50% additional, new and unpublished material compared to their ECU 2023 proceedings paper version. Expanded and high-quality conference papers should fulfill the following requirements: (1) the paper should be expanded to the size of a research article; (2) the conference paper should be cited and noted on the first page of the paper; (3) if the authors do not hold the copyright for the published conference paper, permission must be granted from the copyright holder; (4) authors are asked to disclose that their article is a conference paper in their cover letter and include a statement regarding the changes made to the original conference paper.

We look forward to receiving your contributions.

Prof. Dr. Giacomo Tommei
Prof. Dr. Gerald B. Cleaver
Prof. Dr. Marcello Abbrescia
Prof. Dr. Gonzalo J. Olmo
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 submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. 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 (10 papers)

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Research

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24 pages, 831 KiB  
Article
Jerk Parameter and Modified Theory
by Değer Sofuoğlu and Aroonkumar Beesham
Universe 2023, 9(10), 430; https://doi.org/10.3390/universe9100430 - 27 Sep 2023
Viewed by 941
Abstract
The accelerated expansion of the universe during recent times is well known in cosmology, whereas during early times, there was decelerated expansion. The ΛCDM model is consistent with most observations, but there are some issues with it. In addition, the transition from [...] Read more.
The accelerated expansion of the universe during recent times is well known in cosmology, whereas during early times, there was decelerated expansion. The ΛCDM model is consistent with most observations, but there are some issues with it. In addition, the transition from early deceleration to late-time acceleration cannot be explained by general relativity. Hence, it is worthwhile to examine modified gravity theories to explain this transition and to get a better understanding of dark energy. In this work, dark energy in modified f(R,T) gravity is investigated, where R is the Ricci scalar and T is the trace of the energy momentum tensor. Normally, the simplest form of f(R,T) is used, viz., f(R)=R+λT. In this work, the more complicated form f(R,T)=R+RT is investigated in Friedmann–Lemaître–Robertson–Walker spacetime. This form has not been well studied. Since the jerk parameter in general relativity is constant and j=1, in order to have as small a departure from general relativity as possible, the jerk parameter j=1 is also assumed here. This enables the complete solution for the scale factor to be found. One of these forms is used for a complete analysis and is compared with the usually studied form f(R,T)=R+RT. The solution can also be broken down into a power-law form at early times (deceleration) and an exponential form at late times (acceleration), which makes the analysis simpler. Surprisingly, each of these forms is also a solution to the differential equation j=1 (though they are not solutions to the general solution). The energy conditions are also studied, and plots are provided. It is shown that viable models can be obtained without the need for the introduction of a cosmological constant, which reduces to the ΛCDM at late times. Full article
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11 pages, 721 KiB  
Article
Rotational Curves of the Milky Way Galaxy and Andromeda Galaxy in Light of Vacuum Polarization around Eicheon
by Sergey L. Cherkas and Vladimir L. Kalashnikov
Universe 2023, 9(9), 424; https://doi.org/10.3390/universe9090424 - 21 Sep 2023
Viewed by 906
Abstract
Eicheon properties are discussed. It is shown that the eicheon surface allows setting a boundary condition for the vacuum polarization and obtaining a solution describing the dark matter tail in the Milky Way Galaxy. That is, the dark matter in the Milky Way [...] Read more.
Eicheon properties are discussed. It is shown that the eicheon surface allows setting a boundary condition for the vacuum polarization and obtaining a solution describing the dark matter tail in the Milky Way Galaxy. That is, the dark matter in the Milky Way Galaxy is explained as the F-type of vacuum polarization, which could be treated as dark radiation. The model presented is spherically symmetric, but a surface density of a baryonic galaxy disk is taken into account approximately by smearing the disk over a sphere. This allows the reproduction of the large distance shape of the Milky Way Galaxy rotational curve. Andromeda Galaxy’s rotational curve is also discussed. Full article
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16 pages, 814 KiB  
Article
Plane Symmetric Cosmological Model with Strange Quark Matter in f(R,T) Gravity
by Vijay Singh, Siwaphiwe Jokweni and Aroonkumar Beesham
Universe 2023, 9(9), 408; https://doi.org/10.3390/universe9090408 - 06 Sep 2023
Viewed by 908
Abstract
A plane symmetric Bianchi-I model filled with strange quark matter (SQM) was explored in f(R,T)=R+2λT gravity, where R is the Ricci scalar, T is the trace of the energy-momentum tensor, and λ [...] Read more.
A plane symmetric Bianchi-I model filled with strange quark matter (SQM) was explored in f(R,T)=R+2λT gravity, where R is the Ricci scalar, T is the trace of the energy-momentum tensor, and λ is an arbitrary constant. Three different types of solutions were obtained. In each model, comparisons of the outcomes in f(R,T) gravity and bag constant were made to comprehend their roles. The first power-law solution was obtained by assuming that the expansion scalar is proportional to the shear scalar. This solution was compared with a similar one obtained earlier. The second solution was derived by assuming a constant deceleration parameter q. This led to two solutions: one power-law and the other exponential. Just as in the case of general relativity, we can obtain solutions for each of the different eras of the universe, but we cannot obtain a model which shows transitional behavior from deceleration to acceleration. However, the third solution is a hybrid solution, which shows the required transition. The models start off with anisotropy, but are shear free at late times. In general relativity, the effect of SQM is to accelerate the universe, so we expect the same in f(R,T) gravity. Full article
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13 pages, 2525 KiB  
Article
Primordial Planets with an Admixture of Dark Matter Particles and Baryonic Matter
by O. V. Kiren, Arun Kenath and Chandra Sivaram
Universe 2023, 9(9), 401; https://doi.org/10.3390/universe9090401 - 31 Aug 2023
Viewed by 780
Abstract
It has been suggested that primordial planets could have formed in the early universe and the missing baryons in the universe could be explained by primordial free-floating planets of solid hydrogen. Many such planets were recently discovered around the old and metal-poor stars, [...] Read more.
It has been suggested that primordial planets could have formed in the early universe and the missing baryons in the universe could be explained by primordial free-floating planets of solid hydrogen. Many such planets were recently discovered around the old and metal-poor stars, and such planets could have formed in early epochs. Another possibility for missing baryons in the universe could be that these baryons are admixed with DM particles inside the primordial planets. Here, we discuss the possibility of the admixture of baryons in the DM primordial planets discussed earlier. We consider gravitationally bound DM objects with the DM particles constituting them varying in mass from 20 to100 GeV. Different fractions of DM particles mixed with baryonic matter in forming the primordial planets are discussed. For the different mass range of DM particles forming DM planets, we have estimated the radius and density of these planets with different fractions of DM and baryonic particles. It is found that for heavier-mass DM particles with the admixture of certain fractions of baryonic particles, the mass of the planet increases and can reach or even substantially exceed Jupiter mass. The energy released during the process of merger of such primordial planets is discussed. The energy required for the tidal breakup of such an object in the vicinity of a black hole is also discussed. Full article
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15 pages, 4607 KiB  
Article
Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation
by Riccardo Nicolaidis, Francesco Nozzoli, Giancarlo Pepponi, Pierluigi Bellutti, Evgeny Demenev, Francesco Maria Follega, Roberto Iuppa and Veronica Vilona
Universe 2023, 9(7), 331; https://doi.org/10.3390/universe9070331 - 11 Jul 2023
Viewed by 699
Abstract
An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from [...] Read more.
An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from Van Allen belts. In this work, the project of a CubeSat space spectrometer, the low-energy module (LEM), is shown. The detector will be able to perform an event-based measurement of the energy, arrival direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows for photon detection in the sub-MeV range, joining the quest for the investigation of the nature of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs). The particle identification of the LEM relies on the ΔEE technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10 × 10 × 10 cm3 CubeSat frame, and it will be constructed as a joint project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements, an innovative approach, based on active particle collimation, was designed for the LEM; this avoids the heavy/bulky passive collimators of previous space detectors. In this paper, we will present the LEM geometry, its detection concept, the results from the developed GEANT4 simulation, and some characterisations of a candidate silicon detector for the instrument payload. Full article
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16 pages, 579 KiB  
Article
QCD Phase Structure and In-Medium Modifications of Meson Masses in Polyakov Linear-Sigma Model with Finite Isospin Asymmetry
by Abdel Nasser Tawfik
Universe 2023, 9(6), 276; https://doi.org/10.3390/universe9060276 - 08 Jun 2023
Cited by 2 | Viewed by 691
Abstract
In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (σ¯3=fK±fK0) and the third generator of the matrix of the explicit symmetry breaking [ [...] Read more.
In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (σ¯3=fK±fK0) and the third generator of the matrix of the explicit symmetry breaking [h3=ma02fK±fK0] are estimated in terms of the decay constants of the neutral (fK0) and charged Kaon (fK±) and the mass of a0 meson. Both quantities σ¯3 and h3 are then evaluated, at finite baryon (μB), isospin chemical potential (μI), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (TμI) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (σ¯3=fK±fK0) and the third generator of the matrix of the explicit symmetry breaking [h3=ma02fK±fK0] are estimated in terms of the decay constants of the neutral (fK0) and charged Kaon (fK±) and the mass of a0 meson. Both quantities σ¯3 and h3 are then evaluated, at finite baryon (μB), isospin chemical potential (μI), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (TμI) phase diagram. The in-medium modifications of pseudoscalars (Jpc=0+), scalars (Jpc=0++), vectors (Jpc=1), and axial-vectors (Jpc=1++) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram (TμI) is qualitatively similar to the (TμB) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states a0, σ, η, π, f0, κ, η, K, ρ, ω, κ*, ϕ, a1, f1, K*, and f1*. Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase. Full article
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15 pages, 5209 KiB  
Article
A Theory about a Hidden Evander-Size Impact and the Renewal of the Intermediate Cratered Terrain on Dione
by Balázs Bradák, Mayuko Nishikawa and Christopher Gomez
Universe 2023, 9(6), 247; https://doi.org/10.3390/universe9060247 - 24 May 2023
Cited by 2 | Viewed by 694
Abstract
The study introduces a theory about an Evander-size impact on the surface of Dione. Our study suspects a relatively low-velocity (≤5 km/s) collision between a ca. 50–80 km diameter object and Dione, which might have resulted in the resurfacing of one of the [...] Read more.
The study introduces a theory about an Evander-size impact on the surface of Dione. Our study suspects a relatively low-velocity (≤5 km/s) collision between a ca. 50–80 km diameter object and Dione, which might have resulted in the resurfacing of one of the satellite’s intermediate cratered terrains in various ways, such as surface planing by “plowing” by ricocheting ejectiles, ejecta blanket covering, partial melting, and impact-triggered diapir formation associated with cryotectonism and effusive cryo-slurry outflows. Modeling the parameters of an impact of such a size and mapping the potential secondary crater distribution in the target location may function as the first test of plausibility to reveal the location of such a collision, which may be hidden by younger impact marks formed during, e.g., the Antenor, Dido, Romulus, and Remus collision events. The source of the impactor might have been Saturn-specific planetocentric debris, a unique impactor population suspected in the Saturnian system. Other possible candidates are asteroid(s) appearing during the outer Solar System’s heavy bombardment period, or a collision, which might have happened during the “giant impact phase” in the early Saturnian system. Full article
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18 pages, 2518 KiB  
Article
Decoupled Anisotropic Solutions Using Karmarkar Condition in f(G, T) Gravity
by Komal Hassan and Muhammad Sharif
Universe 2023, 9(4), 165; https://doi.org/10.3390/universe9040165 - 29 Mar 2023
Cited by 6 | Viewed by 749
Abstract
In this paper, we compute two anisotropic static spherical solutions for two compact stellar candidates in the background of f(G,T) gravity using the minimal geometric decoupling technique. The internal structure becomes anisotropic when an additional sector is added [...] Read more.
In this paper, we compute two anisotropic static spherical solutions for two compact stellar candidates in the background of f(G,T) gravity using the minimal geometric decoupling technique. The internal structure becomes anisotropic when an additional sector is added to the isotropic system. With this method, the radial component is distorted to establish two sets of the field equations that represent perfect and anisotropic sources. We use the Karmarkar condition to formulate the metric potentials that help to find the solution of the first set. For the second set, two extra constraints are applied on theanisotropic sector to find its solution. Both of the solutions are then combined to yield the ultimate anisotropic solution. We then examine the physical feasibility and stability of the resulting anisotropic solutions through energy conditions and stability criteria, respectively. It is found that the compact star Her X-1 is viable but not stable corresponding to the first solution while satisfying all the physical acceptability conditions for the second solution. On the other hand, the star 4U 1820-30 indicates viable and stable behavior for both anisotropic solutions. Full article
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Review

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9 pages, 1355 KiB  
Review
The Andromeda Galaxy and Its Star Formation History
by Denis Leahy
Universe 2023, 9(8), 349; https://doi.org/10.3390/universe9080349 - 26 Jul 2023
Viewed by 1220
Abstract
The state of knowledge of the properties of the Andromeda Galaxy (also known as M31) is reviewed. The spatial structure of the Andromeda Galaxy, its main source populations, and the properties of its gas and dust are discussed. To understand the formation history [...] Read more.
The state of knowledge of the properties of the Andromeda Galaxy (also known as M31) is reviewed. The spatial structure of the Andromeda Galaxy, its main source populations, and the properties of its gas and dust are discussed. To understand the formation history of the Andromeda Galaxy, the critical issues of its star formation history and the gas streams and dwarf galaxies in its surrounding environment are reviewed. Emphasis is on recent studies, with important earlier work described in the references provided here. It is important to understand the Andromeda Galaxy because it is the nearest large external galaxy and is close enough for high-resolution studies. This allows the Andromeda Galaxy to be used as a template for understanding more distant and less resolved galaxies in the universe. Full article
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20 pages, 1972 KiB  
Review
The Zoo of Isolated Neutron Stars
by Sergei B. Popov
Universe 2023, 9(6), 273; https://doi.org/10.3390/universe9060273 - 06 Jun 2023
Cited by 4 | Viewed by 1007
Abstract
In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. [...] Read more.
In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. Several scenarios of magneto-rotational evolution are presented. Recent observational data, such as the discovery of long-period radio pulsars, require the non-trivial evolution of magnetic fields, the spin periods of neutron stars, or both. In some detail, I discuss different models of magnetic field decay and interactions of young neutron stars with fallback matter. Full article
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