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Universe, Volume 10, Issue 3 (March 2024) – 50 articles

Cover Story (view full-size image): In this article, we present a timing analysis of 85 pulsars observed with the Nanshan radio telescope from July 2002 to March 2014. The Cholesky method can accurately estimate the covariance function of the timing residuals, significantly improving the accuracy of parameter estimation when red noise is prominent. We utilize the Cholesky method to determine the positions and basic timing parameters of these pulsars, as well as to obtain timing residuals. Most of these sources showed evidence of significant timing irregularities, which are described. Spectral analyses of timing residuals are presented for pulsars exhibiting obvious red noise. Our results show that timing residuals in half of these pulsars are attributed to rotational irregularities. The red noise in normal pulsars may originate from a random walk in the spin frequency or spin-down rate. View this paper
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26 pages, 17785 KiB  
Article
The κ-Model under the Test of the SPARC Database
by Gianni Pascoli
Universe 2024, 10(3), 151; https://doi.org/10.3390/universe10030151 - 21 Mar 2024
Viewed by 626
Abstract
Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the κ-model. An additional connection, between the κ-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted [...] Read more.
Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the κ-model. An additional connection, between the κ-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter, a0, appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and κ-model) and/or to the dimension of the object under consideration (NFDG and κ-model). We then confer to parameter a0 a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the κ-model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The κ-model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")
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43 pages, 596 KiB  
Article
Emergent Spacetime and Cosmic Inflation
by Hyun Seok Yang
Universe 2024, 10(3), 150; https://doi.org/10.3390/universe10030150 - 21 Mar 2024
Cited by 13 | Viewed by 979
Abstract
We present a novel background-independent framework for cosmic inflation, starting with a matrix model. In this framework, inflation is portrayed as a dynamic process responsible for the generation of both space and time. This stands in contrast to conventional inflation, which is characterized [...] Read more.
We present a novel background-independent framework for cosmic inflation, starting with a matrix model. In this framework, inflation is portrayed as a dynamic process responsible for the generation of both space and time. This stands in contrast to conventional inflation, which is characterized as a mere (exponential) expansion of an already existing spacetime, driven by the vacuum energy associated with an inflaton field. We observe that the cosmic inflation is triggered by the condensate of Planck energy into a vacuum and responsible for the dynamical emergence of spacetime. The emergent spacetime picture admits a background-independent formulation so that the inflation is described by a conformal Hamiltonian system which requires neither an inflaton field nor an ad hoc inflation potential. This implies that the emergent spacetime may incapacitate all the rationales to introduce the multiverse hypothesis. Full article
(This article belongs to the Special Issue Mathematical Cosmology)
32 pages, 733 KiB  
Review
High-Energy and Ultra-High-Energy Neutrino Astrophysics
by Damiano F. G. Fiorillo
Universe 2024, 10(3), 149; https://doi.org/10.3390/universe10030149 - 20 Mar 2024
Viewed by 671
Abstract
The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a [...] Read more.
The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a diffuse flux of astrophysical neutrinos in the TeV-PeV energy range, likely produced in astrophysical sources accelerating cosmic rays, and more recently it has reported on a few candidate individual neutrino sources. Future experiments will be able to improve on these measurements quantitatively, by the detection of more events, and qualitatively, by extending the measurement into the EeV energy range. In this paper, we review the main features of the neutrino emission and sources observed by IceCube, as well as the main candidate sources that could contribute to the diffuse neutrino flux. As a parallel question, we review the status of high-energy neutrinos as a probe of Beyond the Standard Model physics coupling to the neutrino sector. Full article
(This article belongs to the Special Issue Neutrinos across Different Energy Scales)
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30 pages, 1088 KiB  
Review
The Physics of Core-Collapse Supernovae: Explosion Mechanism and Explosive Nucleosynthesis
by Luca Boccioli and Lorenzo Roberti
Universe 2024, 10(3), 148; https://doi.org/10.3390/universe10030148 - 19 Mar 2024
Cited by 3 | Viewed by 772
Abstract
Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star, [...] Read more.
Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star, as well as to explore the vast parameter space of supernovae. Nonetheless, many uncertainties still affect the late stages of the evolution of massive stars, their collapse, and the subsequent shock propagation. In this review, we will briefly summarize the state-of-the-art of both 1D and 3D simulations and how they can be employed to study the evolution of massive stars, supernova explosions, and shock propagation, focusing on the uncertainties that affect each of these phases. Finally, we will illustrate the typical nucleosynthesis products that emerge from the explosion. Full article
(This article belongs to the Special Issue Recent Outcomes and Future Challenges in Nuclear Astrophysics)
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12 pages, 269 KiB  
Article
Conformally Invariant Gravity and Gravitating Mirages
by Victor Berezin and Inna Ivanova
Universe 2024, 10(3), 147; https://doi.org/10.3390/universe10030147 - 17 Mar 2024
Viewed by 692
Abstract
The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law [...] Read more.
The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law imposes quite strict restrictions on the possible types of sources. It is shown that combinations with the particle number density in the creation law can be interpreted as dark matter within the framework of this model. Full article
(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
20 pages, 4360 KiB  
Review
The ASTRI Mini-Array: A New Pathfinder for Imaging Cherenkov Telescope Arrays
by Salvatore Scuderi
Universe 2024, 10(3), 146; https://doi.org/10.3390/universe10030146 - 16 Mar 2024
Cited by 1 | Viewed by 847
Abstract
The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host [...] Read more.
The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host agreement with INAF and, as such, it will be the largest IACT array until the Cherenkov Telescope Array Observatory starts operations. Implementing the ASTRI Mini-Array poses several challenges from technical, logistic, and management points of view. Starting from the description of the innovative technologies adopted to build the telescopes, we will discuss the solutions adopted to overcome these challenges, making the ASTRI Mini-Array a great instrument to perform deep observations of the galactic and extra-galactic sky at very high energies. Full article
(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)
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31 pages, 8707 KiB  
Article
Multiple SSO Space Debris Flyby Trajectory Design Based on Cislunar Orbit
by Siyang Zhang and Shuquan Wang
Universe 2024, 10(3), 145; https://doi.org/10.3390/universe10030145 - 16 Mar 2024
Viewed by 761
Abstract
This paper investigates the trajectory design problem in the scenario of a multiple Sun-synchronous Orbit (SSO) space debris flyby mission from a DRO space station. At first, the characteristics of non-planar transfer from DRO to SSO in the Earth–Moon system are analyzed. The [...] Read more.
This paper investigates the trajectory design problem in the scenario of a multiple Sun-synchronous Orbit (SSO) space debris flyby mission from a DRO space station. At first, the characteristics of non-planar transfer from DRO to SSO in the Earth–Moon system are analyzed. The methods of large-scale ergodicity and pruning are utilized to investigate single-impulse and two-impulse DRO–Earth transfers. Using a powered lunar flyby, the two-impulse DRO–Earth transfer is able to fly by SSO debris while satisfying the requirements of the mission. After the local optimization, the optimal result of two-impulse DRO–Earth transfer and flyby is obtained. A multi-objective evolutionary algorithm is used to design the Pareto-optimal trajectories of multiple flybys. The semi-analytical optimization method is developed to provide the estimations of the transfer parameters in order to reduce the computations caused by the evolutionary algorithm. Simulations show that transferring from the 3:2 resonant DRO to a near-coplanar flyby of a SSO target debris using a powered lunar gravity assist needs a 0.47 km/s velocity increment. The mission’s total velocity increment is 1.39 km/s, and the total transfer time is 2.23 years. Full article
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6 pages, 201 KiB  
Editorial
Origins and Natures of Inflation, Dark Matter and Dark Energy
by Kazuharu Bamba
Universe 2024, 10(3), 144; https://doi.org/10.3390/universe10030144 - 15 Mar 2024
Viewed by 1072
Abstract
Various precise cosmological observations, e [...] Full article
(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy)
19 pages, 755 KiB  
Article
The Relevance of Dynamical Friction for the MW/LMC/SMC Triple System
by Wolfgang Oehm and Pavel Kroupa
Universe 2024, 10(3), 143; https://doi.org/10.3390/universe10030143 - 14 Mar 2024
Viewed by 731
Abstract
Simulations of structure formation in the standard cold dark matter cosmological model quantify the dark matter halos of galaxies. Taking into account dynamical friction between dark matter halos, we investigate the past orbital dynamical evolution of the Magellanic Clouds in the presence of [...] Read more.
Simulations of structure formation in the standard cold dark matter cosmological model quantify the dark matter halos of galaxies. Taking into account dynamical friction between dark matter halos, we investigate the past orbital dynamical evolution of the Magellanic Clouds in the presence of the Galaxy. Our calculations are based on a three-body model of rigid Navarro–Frenk–White profiles for dark matter halos but were verified in a previous publication by comparison to high-resolution N-body simulations of live self-consistent systems. Under the requirement that the LMC and SMC had an encounter within 20 kpc between 1 and 4 Gyr ago in order to allow the development of the Magellanic Stream, using the latest astrometric data, the dynamical evolution of the MW/LMC/SMC system is calculated backwards in time. With the employment of the genetic algorithm and a Markov-Chain Monte-Carlo method, the present state of this system is unlikely, with a probability of <109 (6σ complement), because the solutions found do not fit into the error bars for the observed plane-of-sky velocity components of the Magellanic Clouds. This implies that orbital solutions that assume dark matter halos, according to cosmological structure formation theory, to exist around the Magellanic Clouds and the Milky Way are not possible with a confidence of more than 6 sigma. Full article
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11 pages, 272 KiB  
Article
On the Apparent Discretization of Spacetime and Its Connection with the Cosmological Constant
by Jaume Giné and Giuseppe Gaetano Luciano
Universe 2024, 10(3), 142; https://doi.org/10.3390/universe10030142 - 14 Mar 2024
Viewed by 718
Abstract
The emergence of a minimal observable length of order of the Planck scale is a prediction of many quantum theories of gravity. However, the question arises as to whether this is a real fundamental length affecting nature in all of its facets, including [...] Read more.
The emergence of a minimal observable length of order of the Planck scale is a prediction of many quantum theories of gravity. However, the question arises as to whether this is a real fundamental length affecting nature in all of its facets, including spacetime. In this work, we show that the quantum measurement process implies the existence of a minimal measurable length and consequently the apparent discretization of spacetime. The obtained result is used to infer the value of zero-point energy in the universe, which is found to be in good agreement with the observed cosmological constant. This potentially offers some hints towards the resolution of the cosmological constant problem. Full article
(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)
21 pages, 2026 KiB  
Article
Constraining the Initial Mass Function in the Epoch of Reionization from Astrophysical and Cosmological Data
by Andrea Lapi, Giovanni Gandolfi, Lumen Boco, Francesco Gabrielli, Marcella Massardi, Balakrishna S. Haridasu, Carlo Baccigalupi, Alessandro Bressan and Luigi Danese
Universe 2024, 10(3), 141; https://doi.org/10.3390/universe10030141 - 13 Mar 2024
Viewed by 883
Abstract
We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe based on various ingredients: the latest determination of the UV galaxy luminosity [...] Read more.
We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe based on various ingredients: the latest determination of the UV galaxy luminosity function from JWST out to redshift z12; data-inferred and simulation-driven assumptions on the redshift-dependent escape fraction of ionizing photons from primordial galaxies; a simple yet flexible parameterization of the IMF ϕ(m)mξem,c/m in terms of a high-mass end slope ξ<0 and a characteristic mass m,c, below which a flattening or a bending sets in (allowing description of a variety of IMF shapes from the classic Salpeter to top-heavy ones); the PARSEC stellar evolution code to compute the UV and ionizing emission from different stars’ masses as a function of age and metallicity; and a few physical constraints related to stellar and galaxy formation in faint galaxies at the reionization redshifts. We then compare our model outcomes with the reionization observables from different astrophysical and cosmological probes and perform Bayesian inference on the IMF parameters via a standard MCMC technique. We find that the IMF slope ξ is within the range from 2.8 to 2.3, consistent with direct determination from star counts in the Milky Way, while appreciably flatter slopes are excluded at great significance. However, the bestfit value of the IMF characteristic mass m,c∼a few M implies a suppression in the formation of small stellar masses at variance with the IMF in the local Universe. This may be induced by the thermal background of ∼20–30 K provided by CMB photons at the reionization redshifts. We check that our results are robust against different parameterizations for the redshift evolution of the escape fraction. Finally, we investigate the implications of our reconstructed IMF for the recent JWST detections of massive galaxies at and beyond the reionization epoch, showing that any putative tension with the standard cosmological framework is substantially alleviated. Full article
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31 pages, 1805 KiB  
Article
A Critical Discussion on the H0 Tension
by Salvatore Capozziello, Giuseppe Sarracino and Giulia De Somma
Universe 2024, 10(3), 140; https://doi.org/10.3390/universe10030140 - 13 Mar 2024
Viewed by 908
Abstract
A critical discussion on the H0 Hubble constant tension is presented by considering both early and late-type observations. From recent precise measurements, discrepancies emerge when comparing results for some cosmological quantities obtained at different redshifts. We highlight the most relevant measurements of [...] Read more.
A critical discussion on the H0 Hubble constant tension is presented by considering both early and late-type observations. From recent precise measurements, discrepancies emerge when comparing results for some cosmological quantities obtained at different redshifts. We highlight the most relevant measurements of H0 and propose potential ideas to solve its tension. These solutions concern the exploration of new physics beyond the ΛCDM model or the evaluation of H0 by other methods. In particular, we focus on the role of the look-back time. Full article
(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
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7 pages, 789 KiB  
Communication
Nuclear Modification Factor of Inclusive Charged Particles in Au+Au Collisions at sNN = 27 GeV with the STAR Experiment
by Alisher Aitbayev
Universe 2024, 10(3), 139; https://doi.org/10.3390/universe10030139 - 13 Mar 2024
Viewed by 711
Abstract
The Beam Energy Scan (BES) program at RHIC aims to explore the QCD phase diagram, including the search for the evidence of the 1st order phase transition from hadronic matter to Quark-Gluon Plasma (QGP) and the location of the QCD critical point. One [...] Read more.
The Beam Energy Scan (BES) program at RHIC aims to explore the QCD phase diagram, including the search for the evidence of the 1st order phase transition from hadronic matter to Quark-Gluon Plasma (QGP) and the location of the QCD critical point. One of the features previously observed in the study of QGP is the effect of suppression of particle production with high transverse momenta pT (>2 GeV/c) at energies sNN = 62.4200 GeV, which was deduced from the charged-particle nuclear modification factor (RCP) measured using the data from Beam Energy Scan Program Phase I (BES-I) of STAR experiment. In 2018, STAR has collected over 500 million events from Au+Au collisions at sNN = 27 GeV as a part of the STAR BES-II program, which is about a factor of 10 higher than BES-I 27 GeV data size. In this report, we present new measurements of charged particle production and the nuclear modification factor RCP, from this new 27 GeV data set and compare them with the BES-I results. The new measurements extend the previous BES-I results to higher transverse momentum range, which allows better exploration of the jet quenching effects at low RHIC energies, and may help to understand the effects of the formation and properties of QGP at these energies. Full article
(This article belongs to the Special Issue Multiparticle Dynamics)
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16 pages, 9561 KiB  
Article
Classification of Planetary Motion around Super-Jupiters and Brown Dwarfs
by Euaggelos E. Zotos, Eman M. Moneer and Tobias C. Hinse
Universe 2024, 10(3), 138; https://doi.org/10.3390/universe10030138 - 13 Mar 2024
Viewed by 759
Abstract
We investigate the orbital dynamics of an exosystem consisting of a solar-mass host star, a transiting body, and an Earth-size exoplanet within the framework of the generalized three-body problem. Depending on its mass, the transiting body can either be a super-Jupiter or a [...] Read more.
We investigate the orbital dynamics of an exosystem consisting of a solar-mass host star, a transiting body, and an Earth-size exoplanet within the framework of the generalized three-body problem. Depending on its mass, the transiting body can either be a super-Jupiter or a brown dwarf. To determine the final states of the Earth-size exoplanet, we conduct a systematic and detailed classification of the available phase space trajectories. Our classification scheme distinguishes between the bounded, escape, and collisional motions of the Earth-size exoplanet. Additionally, for cases of ordered (regular) motion, we further categorize the associated initial conditions based on the geometry of their respective trajectories. These bounded regular trajectories hold significant importance as they provide insights into the regions of phase space where the motion of the Earth-size exoplanet can be dynamically stable. Of particular interest is the identification of initial conditions that result in a bounded exomoon-like orbit of the Earth-size exoplanet around the transiting body. Full article
(This article belongs to the Special Issue Formation and Evolution of Exoplanets)
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13 pages, 285 KiB  
Article
Regular Friedmann Universes and Matter Transformations
by Alexander Kamenshchik and Polina Petriakova
Universe 2024, 10(3), 137; https://doi.org/10.3390/universe10030137 - 13 Mar 2024
Viewed by 754
Abstract
We apply a very simple procedure to construct non-singular cosmological models for flat Friedmann universes filled with minimally coupled scalar fields or by tachyon Born–Infeld-type fields. Remarkably, for the minimally coupled scalar field and the tachyon field, the regularity of the cosmological evolution, [...] Read more.
We apply a very simple procedure to construct non-singular cosmological models for flat Friedmann universes filled with minimally coupled scalar fields or by tachyon Born–Infeld-type fields. Remarkably, for the minimally coupled scalar field and the tachyon field, the regularity of the cosmological evolution, or in other words, the existence of bounce, implies the necessity of the transition between scalar fields with standard kinetic terms to those with phantom ones. In both cases, the potentials in the vicinity of the point of the transition have a non-analyticity of the cusp form that is characterized by the same exponent and is equal to 23. If, in the tachyon model’s evolution, the pressure changes its sign, then another transformation of the Born–Infeld-type field occurs: the tachyon transforms into a pseudotachyon, and vice versa. We also undertake an analysis of the stability of the cosmological evolution in our models; we rely on the study of the speed of sound squared. Full article
(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
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12 pages, 280 KiB  
Article
The Quantum Hall Effect under the Influence of Gravity and Inertia: A Unified Approach
by Alexandre Landry, Fayçal Hammad and Reza Saadati
Universe 2024, 10(3), 136; https://doi.org/10.3390/universe10030136 - 13 Mar 2024
Viewed by 817
Abstract
The quantum Hall effect under the influence of gravity and inertia is studied in a unified way. We make use of an algebraic approach, as opposed to an analytic approach. We examine how both the integer and the fractional quantum Hall effects behave [...] Read more.
The quantum Hall effect under the influence of gravity and inertia is studied in a unified way. We make use of an algebraic approach, as opposed to an analytic approach. We examine how both the integer and the fractional quantum Hall effects behave under a combined influence of gravity and inertia using a unified Hamiltonian. For that purpose, we first re-derive, using the purely algebraic method, the energy spectrum of charged particles moving in a plane perpendicular to a constant and uniform magnetic field either (i) under the influence of a nonlinear gravitational potential or (ii) under the influence of a constant rotation. The general Hamiltonian for describing the combined effect of gravity, rotation and inertia on the electrons of a Hall sample is then built and the eigenstates are obtained. The electrons mutual Coulomb interaction that gives rise to the familiar fractional quantum Hall effect is also discussed within such a combination. Full article
(This article belongs to the Section Gravitation)
15 pages, 1058 KiB  
Review
Isovector Axial Charge and Form Factors of Nucleons from Lattice QCD
by Rajan Gupta
Universe 2024, 10(3), 135; https://doi.org/10.3390/universe10030135 - 12 Mar 2024
Viewed by 710
Abstract
A survey of the calculations of the isovector axial vector form factor of the nucleon using lattice QCD is presented. Attention is paid to statistical and systematic uncertainties, in particular those due to excited state contributions. Based on a comparison of results from [...] Read more.
A survey of the calculations of the isovector axial vector form factor of the nucleon using lattice QCD is presented. Attention is paid to statistical and systematic uncertainties, in particular those due to excited state contributions. Based on a comparison of results from various collaborations, a case is made that lattice results are consistent within 10%. A similar level of uncertainty is in the axial charge gAud, the mean squared axial charge radius rA2, the induced pseudoscalar charge gP, and the pion–nucleon coupling gπNN. Even with the current methodology, a significant reduction in errors is expected over the next few years with higher statistics data on more ensembles closer to the physical point. Lattice QCD results for the form factor GA(Q2) are compatible with those obtained from the recent MINERνA experiment but lie 2–3σ higher than the phenomenological extraction from the old ν–deuterium bubble chamber scattering data for Q2>0.3 GeV2. Current data show that the dipole ansatz does not have enough parameters to fit the form factor over the range 0Q21 GeV2, whereas even a z2 truncation of the z expansion or a low order Padé are sufficient. Looking ahead, lattice QCD calculations will provide increasingly precise results over the range 0Q21 GeV2, and MINERνA-like experiments will extend the range to Q22 GeV2 or higher. Nevertheless, improvements in lattice methods to (i) further control excited state contributions and (ii) extend the range of Q2 are needed. Full article
(This article belongs to the Special Issue Neutron Lifetime)
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16 pages, 1794 KiB  
Article
Weak Coupling Regime in Dilatonic f(R,T) Cosmology
by Francisco A. Brito, Carlos H. A. B. Borges, José A. V. Campos and Francisco G. Costa
Universe 2024, 10(3), 134; https://doi.org/10.3390/universe10030134 - 11 Mar 2024
Viewed by 701
Abstract
We consider f(R,T) modified theories of gravity in the context of string-theory-inspired dilaton gravity. We deal with a specific model that under certain conditions describes the late time Universe in accord with observational data in modern cosmology and [...] Read more.
We consider f(R,T) modified theories of gravity in the context of string-theory-inspired dilaton gravity. We deal with a specific model that under certain conditions describes the late time Universe in accord with observational data in modern cosmology and addresses the H0 tension. This is done by exploring the space of parameters made out of those coming from the modified gravity and dilatonic charge sectors. We employ numerical methods to obtain several important observable quantities. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2023—Cosmology)
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15 pages, 10706 KiB  
Article
Analysis of the Geodesic Motions of Massive Particles in Kerr–Sen–AdS4 Spacetime
by Ziqiang Cai, Ming Liu, Wen-Qian Wang, Tong-Yu He, Zhan-Wen Han and Rong-Jia Yang
Universe 2024, 10(3), 133; https://doi.org/10.3390/universe10030133 - 08 Mar 2024
Viewed by 1112
Abstract
We consider geodesic motions in Kerr–Sen–AdS4 spacetime. We obtain equations of motion for light rays and test particles. Using parametric diagrams, we show some regions where radial and latitudinal geodesic motions are allowed. We analyze the impact of parameters related to the [...] Read more.
We consider geodesic motions in Kerr–Sen–AdS4 spacetime. We obtain equations of motion for light rays and test particles. Using parametric diagrams, we show some regions where radial and latitudinal geodesic motions are allowed. We analyze the impact of parameters related to the dilatonic scalar on the orbit and find that it will result in more rich and complex orbital types. Full article
(This article belongs to the Section Gravitation)
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54 pages, 757 KiB  
Review
Transport Coefficients of Relativistic Matter: A Detailed Formalism with a Gross Knowledge of Their Magnitude
by Ashutosh Dwibedi, Nandita Padhan, Arghya Chatterjee and Sabyasachi Ghosh
Universe 2024, 10(3), 132; https://doi.org/10.3390/universe10030132 - 07 Mar 2024
Viewed by 903
Abstract
The present review article has attempted a compact formalism description of transport coefficient calculations for relativistic fluid, which is expected in heavy ion collision experiments. Here, we first address the macroscopic description of relativistic fluid dynamics and then its microscopic description based on [...] Read more.
The present review article has attempted a compact formalism description of transport coefficient calculations for relativistic fluid, which is expected in heavy ion collision experiments. Here, we first address the macroscopic description of relativistic fluid dynamics and then its microscopic description based on the kinetic theory framework. We also address different relaxation time approximation-based models in Boltzmann transport equations, which make a sandwich between Macro and Micro frameworks of relativistic fluid dynamics and finally provide different microscopic expressions of transport coefficients like the fluid’s shear viscosity and bulk viscosity. In the numeric part of this review article, we put stress on the two gross components of transport coefficient expressions: relaxation time and thermodynamic phase-space part. Then, we try to tune the relaxation time component to cover earlier theoretical estimations and experimental data-driven estimations for RHIC and LHC matter. By this way of numerical understanding, we provide the final comments on the values of transport coefficients and relaxation time in the context of the (nearly) perfect fluid nature of the RHIC or LHC matter. Full article
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9 pages, 245 KiB  
Article
On Phase Transitions during Collisions near the Horizon of Black Holes
by Andrey A. Grib and Yuri V. Pavlov
Universe 2024, 10(3), 131; https://doi.org/10.3390/universe10030131 - 07 Mar 2024
Viewed by 768
Abstract
During particle collisions in the vicinity of the horizon of black holes, it is possible to achieve energies and temperatures corresponding to phase transitions in particle physics. It is shown that the sizes of the regions of the new phase are of the [...] Read more.
During particle collisions in the vicinity of the horizon of black holes, it is possible to achieve energies and temperatures corresponding to phase transitions in particle physics. It is shown that the sizes of the regions of the new phase are of the order of the Compton length for the corresponding mass scale. The lifetime is also on the order of the Compton time. It is shown that the inverse influence of the energy density in the electro-weak phase transition in collisions on the space–time metric can be neglected. Full article
(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
29 pages, 3696 KiB  
Review
The Modeling of Pulsar Magnetosphere and Radiation
by Gang Cao, Xiongbang Yang and Li Zhang
Universe 2024, 10(3), 130; https://doi.org/10.3390/universe10030130 - 07 Mar 2024
Viewed by 885
Abstract
We review the recent advances in the pulsar high-energy γ-ray observation and the electrodynamics of the pulsar magnetospheres from the early vacuum model to the recent plasma-filled models by numerical simulations. The numerical simulations have made significant progress toward the self-consistent modeling [...] Read more.
We review the recent advances in the pulsar high-energy γ-ray observation and the electrodynamics of the pulsar magnetospheres from the early vacuum model to the recent plasma-filled models by numerical simulations. The numerical simulations have made significant progress toward the self-consistent modeling of the plasma-filled magnetosphere by including the particle acceleration and radiation. The current numerical simulations confirm a near force-free magnetosphere with the particle acceleration in the separatrix near the light cylinder and the current sheet outside the light cylinder, which can provide a good match to the recent high-energy γ-ray observations. The modeling of the combined multi-wavelength light curves, spectra, and polarization are expected to provide a stronger constrain on the geometry of the magnetic field lines, the location of the particle acceleration and the emission region, and the emission mechanism in the pulsar magnetospheres. Full article
(This article belongs to the Special Issue Pulsar Astronomy)
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16 pages, 505 KiB  
Article
A Simple Direct Empirical Observation of Systematic Bias of the Redshift as a Distance Indicator
by Lior Shamir
Universe 2024, 10(3), 129; https://doi.org/10.3390/universe10030129 - 06 Mar 2024
Viewed by 950
Abstract
Recent puzzling observations, such as the H0 tension, large-scale anisotropies, and massive disk galaxies at high redshifts, have been challenging the standard cosmological model. While one possible explanation is that the standard model is incomplete, other theories are based on the contention [...] Read more.
Recent puzzling observations, such as the H0 tension, large-scale anisotropies, and massive disk galaxies at high redshifts, have been challenging the standard cosmological model. While one possible explanation is that the standard model is incomplete, other theories are based on the contention that the redshift model as a distance indicator might be biased. These theories can explain the recent observations, but they are challenged by the absence of a direct empirical reproducible observation that the redshift model can indeed be inconsistent. Here, I describe a simple experiment that shows that the spectra of galaxies depend on their rotational velocity relative to the rotational velocity of the Milky Way. Moreover, it shows that the redshift of galaxies that rotate in the opposite direction relative to the Milky Way is significantly smaller compared with the redshift of galaxies that rotate in the same direction relative to the Milky Way (p < 0.006). Three different datasets were used independently, each one was prepared in a different manner, and all of them showed similar redshift bias. A fourth dataset of galaxies from the Southern Galactic pole was also analyzed and shows similar results. All four datasets are publicly available. While a maximum average z difference of ∼0.012 observed with galaxies of relatively low redshift (z < 0.25) is not extreme, the bias is consistent and canpotentially lead to explanations to puzzling observations such as the H0 tension. Full article
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26 pages, 643 KiB  
Article
Re-Examination of the Effect of Pairing Gaps on Gamow–Teller Strength Distributions and β-Decay Rates
by Jameel-Un Nabi, Muhammad Riaz and Arslan Mehmood
Universe 2024, 10(3), 128; https://doi.org/10.3390/universe10030128 - 06 Mar 2024
Viewed by 761
Abstract
β-decay is one of the key factors for understanding the r-process and evolution of massive stars. The Gamow–Teller (GT) transitions drive the β-decay process. We employ the proton–neutron quasiparticle random phase approximation (pn-QRPA) model to calculate terrestrial and stellar β [...] Read more.
β-decay is one of the key factors for understanding the r-process and evolution of massive stars. The Gamow–Teller (GT) transitions drive the β-decay process. We employ the proton–neutron quasiparticle random phase approximation (pn-QRPA) model to calculate terrestrial and stellar β-decay rates for 50 top-ranked nuclei possessing astrophysical significance according to a recent survey. The model parameters of the pn-QRPA model affect the predicted results of β-decay. The current study investigates the effect of nucleon–nucleon pairing gaps on charge-changing transitions and the associated β decay rates. Three different values of pairing gaps, namely TF, 3TF, and 5TF, were used in our investigation. It was concluded that both GT strength distributions and half-lives are sensitive to pairing gap values. The 3TF pairing gap scheme, in our chosen nuclear model, resulted in the best prediction with around 80% of the calculated half-lives within a factor 10 of the measured ones. The 3TF pairing scheme also led to the calculation of the biggest β-decay rates in stellar matter. Full article
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21 pages, 1673 KiB  
Article
Simple Lévy α-Stable Model Analysis of Elastic pp and pp¯ Low-|t| Data from SPS to LHC Energies
by Tamás Csörgő, Sándor Hegyi and István Szanyi
Universe 2024, 10(3), 127; https://doi.org/10.3390/universe10030127 - 06 Mar 2024
Viewed by 737
Abstract
A simple Lévy α-stable (SL) model is used to describe the data on elastic pp and pp¯ scattering at low-|t| from SPS energies up to LHC energies. The SL model is demonstrated to describe the data [...] Read more.
A simple Lévy α-stable (SL) model is used to describe the data on elastic pp and pp¯ scattering at low-|t| from SPS energies up to LHC energies. The SL model is demonstrated to describe the data with a strong non-exponential feature in a statistically acceptable manner. The energy dependence of the parameters of the model is determined and analyzed. The Lévy α parameter of the model has an energy-independent value of 1.959 ± 0.002 following from the strong non-exponential behavior of the data. We strengthen the conclusion that the discrepancy between TOTEM and ATLAS elastic pp differential cross section measurements arises only in the normalization and not in the shape of the distribution of the data as a function of t. We find that the slope parameter has different values for pp and pp¯ elastic scattering at LHC energies. This may be the effect of the odderon exchange or the jump in the energy dependence of the slope parameter in the energy interval 3 GeV s 4 GeV. Full article
(This article belongs to the Special Issue Multiparticle Dynamics)
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9 pages, 2185 KiB  
Communication
Heavy Flavor Physics at the sPHENIX Experiment
by Zhaozhong Shi
Universe 2024, 10(3), 126; https://doi.org/10.3390/universe10030126 - 06 Mar 2024
Viewed by 807
Abstract
The sPHENIX experiment is a state-of-the-art jet and heavy flavor physics detector, which successfully recorded its first Au + Au collision data at 200 GeV at the Relativistic Heavy Ion Collider (RHIC). sPHENIX will provide heavy flavor physics measurements at RHIC, covering an [...] Read more.
The sPHENIX experiment is a state-of-the-art jet and heavy flavor physics detector, which successfully recorded its first Au + Au collision data at 200 GeV at the Relativistic Heavy Ion Collider (RHIC). sPHENIX will provide heavy flavor physics measurements at RHIC, covering an unexplored kinematic region and unprecedented precision, to probe the parton energy loss mechanism, parton transport coefficients in quark–gluon plasma, and the hadronization process under various medium conditions. At the center of sPHENIX, the monolithic active pixel sensor (MAPS)-based VerTeX detector (MVTX) is a high-precision silicon pixel detector. The MVTX provides excellent position resolution and the capability of operating in continuous streaming readout mode, allowing precise vertex determination and recording a large data sample, both of which are particularly crucial for heavy flavor physics measurements. In this work, we will show the general performance of heavy-flavor hadron reconstruction. In addition, we will discuss the commissioning experience with sPHENIX. Finally, we will provide the projection of b-hadron and jet observables and discuss the estimated constraints on theoretical models. Full article
(This article belongs to the Special Issue Multiparticle Dynamics)
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25 pages, 622 KiB  
Article
On Minimal Entanglement Wedge Cross Section for Holographic Entanglement Negativity
by Jaydeep Kumar Basak, Vinay Malvimat, Himanshu Parihar, Boudhayan Paul and Gautam Sengupta
Universe 2024, 10(3), 125; https://doi.org/10.3390/universe10030125 - 05 Mar 2024
Cited by 32 | Viewed by 749
Abstract
We demonstrate the equivalence of two different conjectures in the literature for the holographic entanglement negativity in AdS3/CFT2, modulo certain constants. These proposals involve certain algebraic sums of bulk geodesics homologous to specific combinations of subsystems, and the entanglement [...] Read more.
We demonstrate the equivalence of two different conjectures in the literature for the holographic entanglement negativity in AdS3/CFT2, modulo certain constants. These proposals involve certain algebraic sums of bulk geodesics homologous to specific combinations of subsystems, and the entanglement wedge cross section (EWCS) backreacted by a cosmic brane for the conical defect geometry in the bulk gravitational path integral. It is observed that the former conjectures reproduce the field theory replica technique results in the large central charge limit whereas the latter involves constants related to the Markov gap. In this context, we establish an alternative construction for the EWCS of a single interval in a CFT2 at a finite temperature to resolve an issue for the latter proposal involving thermal entropy elimination for holographic entanglement negativity. Our construction for the EWCS correctly reproduces the corresponding field theory results modulo the Markov gap constant in the large central charge limit. Full article
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5 pages, 192 KiB  
Editorial
Top Quark at the New Physics Frontier
by Efe Yazgan and Pedro Silva
Universe 2024, 10(3), 124; https://doi.org/10.3390/universe10030124 - 05 Mar 2024
Viewed by 709
Abstract
This Special Issue of Universe is devoted to the most massive fundamental elementary particle known, the top quark [...] Full article
(This article belongs to the Special Issue Top Quark at the New Physics Frontier)
27 pages, 389 KiB  
Article
Theoretically Motivated Dark Electromagnetism as the Origin of Relativistic Modified Newtonian Dynamics
by Felix Finster, José M. Isidro, Claudio F. Paganini and Tejinder P. Singh
Universe 2024, 10(3), 123; https://doi.org/10.3390/universe10030123 - 04 Mar 2024
Cited by 1 | Viewed by 750
Abstract
The present paper is a modest attempt to initiate the research program outlined in this abstract. We propose that general relativity and relativistic MOND (RelMOND) are analogues of broken electroweak symmetry. That is, [...] Read more.
The present paper is a modest attempt to initiate the research program outlined in this abstract. We propose that general relativity and relativistic MOND (RelMOND) are analogues of broken electroweak symmetry. That is, SU(2)R×U(1)YDEMU(1)DEM (DEM stands for dark electromagnetism), and GR is assumed to arise from the broken SU(2)R symmetry and is analogous to the weak force. RelMOND is identified with dark electromagnetism U(1)DEM, which is the remaining unbroken symmetry after the spontaneous symmetry breaking of the dark electro-grav sector SU(2)R×U(1)YDEM. This sector, as well as the electroweak sector, arises from the breaking of an E8×E8 symmetry in a recently proposed model of unification of the standard model with pre-gravitation, with the latter based on an SU(2)R gauge theory. The source charge for the dark electromagnetic force is the square root of mass, motivated by the experimental fact that the ratio of the square roots of the masses of the electron, up-quark, and down-quark is 1:2:3, which is the opposite of the ratio of their electric charges at 3:2:1. The introduction of the dark electromagnetic force helps us understand the peculiar mass ratios of the second and third generations of charged fermions. We also note that in the deep MOND regime, acceleration is proportional to the square root of mass, which motivates us to propose the relativistic U(1)DEM gauge symmetry as the origin of MOND. We explain why the dark electromagnetic force falls inversely with distance, as in MOND, rather than following the inverse square of distance. We conclude that dark electromagnetism effectively mimics cold dark matter, and the two are essentially indistinguishable in cosmological situations where CDM successfully explains observations, such as CMB anisotropies and gravitational lensing. Full article
(This article belongs to the Special Issue The Large-Scale Structure of the Universe: Theory and Observation)
90 pages, 11352 KiB  
Review
Observational Constraints on Dynamical Dark Energy Models
by Olga Avsajanishvili, Gennady Y. Chitov, Tina Kahniashvili, Sayan Mandal and Lado Samushia
Universe 2024, 10(3), 122; https://doi.org/10.3390/universe10030122 - 04 Mar 2024
Cited by 2 | Viewed by 837
Abstract
Scalar field ϕCDM models provide an alternative to the standard ΛCDM paradigm, while being physically better motivated. Dynamical scalar field ϕCDM models are divided into two classes: the quintessence (minimally and non-minimally interacting with gravity) and phantom models. These models [...] Read more.
Scalar field ϕCDM models provide an alternative to the standard ΛCDM paradigm, while being physically better motivated. Dynamical scalar field ϕCDM models are divided into two classes: the quintessence (minimally and non-minimally interacting with gravity) and phantom models. These models explain the phenomenology of late-time dark energy. In these models, energy density and pressure are time-dependent functions under the assumption that the scalar field is described by the ideal barotropic fluid model. As a consequence of this, the equation of state parameter of the ϕCDM models is also a time-dependent function. The interaction between dark energy and dark matter, namely their transformation into each other, is considered in the interacting dark energy models. The evolution of the universe from the inflationary epoch to the present dark energy epoch is investigated in quintessential inflation models, in which a single scalar field plays a role of both the inflaton field at the inflationary epoch and of the quintessence scalar field at the present epoch. We start with an overview of the motivation behind these classes of models, the basic mathematical formalism, and the different classes of models. We then present a compilation of recent results of applying different observational probes to constraining ϕCDM model parameters. Over the last two decades, the precision of observational data has increased immensely, leading to ever tighter constraints. A combination of the recent measurements favors the spatially flat ΛCDM model but a large class of ϕCDM models is still not ruled out. Full article
(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy)
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