Universe doi: 10.3390/universe9060256

Authors: Andrzej Góźdź Marek Góźdź Aleksandra Pȩdrak

The problem of quantum time and evolution of quantum systems, where time is not a parameter, is considered. In our model, following some earlier works, time is represented by a quantum operator. In this paper, similarly to the position operators in the Schr&ouml;dinger representation of quantum mechanics, this operator is a multiplication-type operator. It can be also represented by an appropriate positive operator-valued measure (POVM) which together with the 3D position operators/measures provide a quantum observable giving a position in the quantum spacetime. The quantum evolution itself is a stochastic process based on L&uuml;der&rsquo;s projection postulate. In fact, it is a generalization of the unitary evolution. This allows to treat time and generally the spacetime position as a quantum observable, in a consistent and observer-independent way.

]]>Universe doi: 10.3390/universe9060255

Authors: Alnadhief H. A. Alfedeel

Using an open thermodynamic systems theory, the effect of particle creation on the evolution and dynamics of the standard cosmological FLRW model in a higher-dimensional spacetime with functionally dependent cosmological and gravitational constants &Lambda; and G is investigated. The gravitational field equations have been transformed into a dimensionless system of non-linear, first-order, coupled differential equations (DEs) as functions of the universe&rsquo;s density parameters &Omega;i and rate of particle creation &Psi; in redshift space, which can be numerically casted. Two cosmological models are obtained, depending on the choice of particle creation rate&mdash;&Psi;&sim;H2 and &Psi;&sim;n2 for dust-, radiation- and dark-energy-dominated universes, respectively. The dynamic behaviour of each model is discussed.

]]>Universe doi: 10.3390/universe9060253

Authors: Guqiang Li

Taking the generalized uncertainty principle (GUP) into account, we apply the corrected state density to investigate the entropy density, energy density, pressure and equation of state for the perfect relativistic gases of massless particles with an arbitrary spin of s &le; 2 surrounding a new four-dimensional neutral Gauss&ndash;Bonnet black hole. The modifications of these thermodynamic quantities by the gravity correction factor and particle spin are shown, and the expressions have completely different forms from those in flat space-times. For example, the energy density is not proportional to the fourth power of the temperature. In other words, the energy density differs from that of blackbody radiation. The quantum gravity effects reduce these quantities and are proportional to the gravity correction factor. The result that the equation of state is not zero is compatible with the non-vanishing trace of the stress tensor.

]]>Universe doi: 10.3390/universe9060254

Authors: Jian Chen Peng Bi Mingfang Yang

We consider the central configurations of the 1+N-body problem, where N bodies are infinitesimal and the remaining one body is dominant. For regular polygon central configurations, we prove that the masses of all the infinitesimal bodies are equal when N is odd and the masses of the alternate infinitesimal bodies must be equal when N is even. Moreover, in the case of N being even, we present the relationship of the mass parameters between two consecutive infinitesimal bodies.

]]>Universe doi: 10.3390/universe9060252

Authors: Sufen Guo Zhaoxiang Qi

Oort constants and local kinematics are vital parameters with which to study the structure and dynamics of the Milky Way. When GCNS was published, it provided a clean sample of stars in the solar vicinity, which gives us an ideal tool with which to determine these parameters. Our aim was to calculate the reliable Oort constants with GCNS. We determined the Oort constants using the GCNS from Gaia EDR3 with d&lt;100pc. The proper motions and radial velocities were fitted with a maximum likelihood model. The uncertainties were obtained with an MCMC method. The sample was carefully selected to obtain a reliable result. The result yields the Oort constants A=15.6&plusmn;1.6kms&minus;1kpc&minus;1, B=&minus;15.8&plusmn;1.7kms&minus;1kpc&minus;1, C=&minus;3.5&plusmn;1.6kms&minus;1kpc&minus;1, and K=2.7&plusmn;1.5kms&minus;1kpc&minus;1. The non-zero C and K imply that the local disc is in a non-asymmetric potential. With the Oort constants, we derived the local angular velocity &Omega;0&asymp;A&minus;B=31.4&plusmn;2.3kms&minus;1kpc&minus;1. The solar motion (U&#8857;, V&#8857;, W&#8857;) was calculated as (10.1&plusmn;0.1, 22.8&plusmn;0.1, 7.8&plusmn;0.1) kms&minus;1.

]]>Universe doi: 10.3390/universe9060251

Authors: Yuhao Zhu Chenhui Niu Xianghan Cui Di Li Yi Feng Chaowei Tsai Pei Wang Yongkun Zhang Fanyi Meng Zheng Zheng

Fast Radio Bursts (FRBs) are millisecond-duration transient events that are typically observed at radio wavelengths and cosmological distances but their origin remains unclear. Furthermore, most FRB origin models are related to the processes at stellar scales, involving neutron stars, blackholes, supernovae, etc. In this paper, our purpose is to determine whether multi-structural one-off FRBs and repeaters share similarities. To achieve this, we focus on analyzing the relationship between the FRB event rate and the star formation rate, complemented by statistical testing methods. Based on the CHIME/FRB Catalog 1, we calculate the energy functions for four subsamples, including apparent non-repeating FRBs (one-offs), repeaters, multi-structural one-offs, and the joint repeaters and multi-structural events, respectively. We then derive the FRB event rates at different redshifts for all four subsamples, all of which were found to share a similar cosmological evolution trend. However, we find that the multi-structural one-offs and repeaters are distinguishable from the KS and MWW tests.

]]>Universe doi: 10.3390/universe9060250

Authors: Huayu Zhao Ying Liu Qiugang Zong Huigen Yang Zejun Hu Xuzhi Zhou Jicheng Sun

The black aurora is a distinct phenomenon characterized by spatially well-defined regions where the diffuse auroral luminosity decreases notably. Typically, black auroras present as arcs moving at lower velocities, patches with higher moving speeds, and arc segments. However, the mechanism behind black auroras remains unclear. In this paper, we present a novel observation of a poleward-moving black auroral arc associated with impulse-excited field-line resonances in the dawnside sector from the multi-spacecraft THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission, equivalent ionospheric currents, and a conjugated all-sky imager. The field-line resonance velocities exhibit periodic vorticity, which correspond to periodic poleward-moving bands of enhanced FACs. Based on the relatively large reduction in luminosity, we conclude that the poleward-moving black auroral arc was most likely caused by downward FACs associated with field-line resonances.

]]>Universe doi: 10.3390/universe9060249

Authors: Huayu Zhao Ying Liu Huigen Yang Qiugang Zong Zejun Hu Xuzhi Zhou Yongfu Wang Jicheng Sun Bin Li

The theory of equatorward moving east-west elongated auroral arcs associated with field line resonance (FLR) has been proposed for decades. However, confirming this theory requires in-situ observations of FLR within the magnetosphere and simultaneous all-sky imager observations of equatorward moving auroral arcs near satellite footpoints. In this study, we present the first observations of multiple equatorward moving auroral arcs related to impulse-excited FLR, using datasets from the WIND, Geotail satellites, and an all-sky imager at China&rsquo;s Zhongshan Station (ZHS) in Antarctica. In the presented event, the ultra-low-frequency waves associated with solar wind dynamic pressure pulse was mainly toroidal mode, which is consistent with the theory that the toroidal mode waves usually related with external source. The all-sky imager located in Zhongshan station recorded several equatorward moving auroral arcs, followed by reverse propagating ones. The latitudinal width of the equatorward moving auroral arcs was on the order of 25 km and had an average equatorward propagation of ~0.37 km/s, which is very similar to the value from previous work. To better illustrate the observed evolution of auroral arcs related with the FLRs we proposed a simple model to evaluate the FACs induced by the FLRs in different latitudes. The latitudinal distribution evolution of FACs agrees well with the ground-based optical observations.

]]>Universe doi: 10.3390/universe9060248

Authors: Jian Wang Yibo Zhao Cheng Yang Yafei Shi Yulong Hao Haiyan Zhang Jianmin Sun Dingling Luo

In this study, we aim to analyze the electromagnetic interference (EMI) regarding the Five-hundred-meter Aperture Spherical radio Telescope (FAST) caused by base stations in the International Mobile Telecommunications-2000 (IMT-2000) frequency band. By analyzing the frequency bands used by the transmitting and receiving devices and the surrounding environmental parameters and utilizing an approach to predicting radio wave propagation loss that is based on deterministic methods, we conclude by comparing the predicted received power at the FAST with its interference protection threshold. Our analysis demonstrates that, currently, only 55.31% of IMT-2000 base stations in the FAST radio quiet zone (RQZ) meet the protection threshold. Additionally, this article verifies the applicability and accuracy of the radio wave propagation model used in the research based on field strength measurements. Overall, this study provides valuable insights for improving the electromagnetic environment surrounding FAST and reducing the EMI caused by mobile communication base stations. It also provides corresponding analysis methods and useful suggestions for analyzing electromagnetic radiation interference in other radio telescopes.

]]>Universe doi: 10.3390/universe9060247

Authors: Balázs Bradák Mayuko Nishikawa Christopher Gomez

The study introduces a theory about an Evander-size impact on the surface of Dione. Our study suspects a relatively low-velocity (&le;5 km/s) collision between a ca. 50&ndash;80 km diameter object and Dione, which might have resulted in the resurfacing of one of the satellite&rsquo;s intermediate cratered terrains in various ways, such as surface planing by &ldquo;plowing&rdquo; 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&rsquo;s heavy bombardment period, or a collision, which might have happened during the &ldquo;giant impact phase&rdquo; in the early Saturnian system.

]]>Universe doi: 10.3390/universe9060246

Authors: Gabriele U. Varieschi

We apply Newtonian fractional-dimension gravity (NFDG), an alternative gravitational model, to some notable cases of galaxies with little or no dark matter. In the case of the ultra-diffuse galaxy AGC 114905, we show that NFDG methods can effectively reproduce the observed rotation curve using a variable fractional dimension DR, as was performed for other galaxies in previous studies. For AGC 114905, we obtain a variable dimension in the range D&asymp; 2.2&ndash;3.2, but our fixed D = 3 curve can still fit all the experimental data within their error bars. This confirms other studies indicating that the dynamics of this galaxy can be described almost entirely by the baryonic mass distribution alone. In the case of NGC 1052-DF2, we use an argument based on the NFDG extension of the virial theorem applied to the velocity dispersion of globular clusters showing that, in general, discrepancies between observed and predicted velocity dispersions can be attributed to an overall fractal dimension D&lt;3 of the astrophysical structure considered, and not to the presence of dark matter. For NGC 1052-DF2, we estimate D&asymp;2.9, thus confirming that this galaxy almost follows standard Newtonian behavior. We also consider the case of the Bullet Cluster merger (1E0657-56), assumed to be one of the strongest proofs of dark matter existence. A simplified but effective NFDG model of the collision shows that the observed infall velocity of this merger can be explained by a fractional dimension of the system in the range D&#8771; 2.4&ndash;2.5, again, without using any dark matter.

]]>Universe doi: 10.3390/universe9060245

Authors: Eleonora Troja

Swift has now completed 18 years of mission, during which it discovered thousands of gamma-ray bursts as well as new classes of high-energy transient phenomena. Its first breakthrough result was the localization of short duration GRBs, which enabled for redshift measurements and kilonova searches. Swift, in synergy with the Hubble Space Telescope and a wide array of ground-based telescopes, provided the first tantalizing evidence of a kilonova in the aftermath of a short GRB. In 2017, Swift observations of the gravitational wave event GW170817 captured the early UV photons from the kilonova AT2017gfo, opening a new window into the physics of kilonovae. Since then, Swift has continued to expand the sample of known kilonovae, leading to the surprising discovery of a kilonova in a long duration GRB. This article will discuss recent advances in the study of kilonovae driven by the fundamental contribution of Swift.

]]>Universe doi: 10.3390/universe9060244

Authors: József Vinkó Tamás Szalai Réka Könyves-Tóth

The violent stellar explosions known as supernovae have received especially strong attention in both the research community and the general public recently. With the advent of space telescopes, the study of these extraordinary events has switched gears and it has become one of the leading fields in modern astrophysics. In this paper, we review some of the recent developments, focusing mainly on studies related to space-based observations.

]]>Universe doi: 10.3390/universe9050243

Authors: Bijan Saha

Within the scope of a Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model we study the role of a nonlinear spinor field in the evolution of the universe. In doing so, we exploit the FLRW models given in both Cartesian and spherical coordinates. It is found that if the FLRW model is given in the spherical coordinates the energy-momentum tensor (EMT) of the spinor field possesses nontrivial non-diagonal components, which is not the case for Cartesian coordinates. These non-diagonal components do not depend on either the spinor field nonlinearity or the parameter k that defines the type of curvature of the FLRW model. The presence of such components imposes some restrictions on the spinor field. The problem is studied for open, flat and close geometries and the spinor field is used to simulate different types of sources including dark energies. Some qualitative numerical solutions are given.

]]>Universe doi: 10.3390/universe9050242

Authors: Jorgen D’Hondt Tae Jeong Kim

At the LHC, the process of a Higgs boson decaying into bottom or charm quarks produced in association with a pair of top quarks, tt&macr;H, allows for an empirical exploration of the heavy-flavor quark Yukawa couplings to the Higgs boson. Accordingly, the cross-sections for the tt&macr; + heavy-flavor production without the appearance of the Higgs boson have been measured at the LHC in various phase spaces using data samples collected in pp collisions at s = 7, 8 and 13 TeV with the ATLAS and CMS experiments. Flavor ratios of cross-sections of tt&macr; + heavy-flavors to tt&macr; + additionaljets processes are also measured. In this paper, the measured cross-sections and ratios are reviewed and the prospects with more data are presented.

]]>Universe doi: 10.3390/universe9050241

Authors: Robson A. Dantas Herondy F. Santana Mota Eugênio R. Bezerra de Mello

In this paper, we investigate the bosonic Casimir effect in a Lorentz-violating symmetry scenario. The theoretical model adopted consists of a real massive scalar quantum field confined in a region between two large parallel plates, having its dynamics governed by a modified Klein&ndash;Gordon equation that presents a Lorentz symmetry-breaking term. In this context, we admit that the quantum field obeys specific boundary conditions on the plates. The Lorentz-violating symmetry is implemented by the presence of an arbitrary constant space-like vector in a CPT-even aether-like approach, considering a direct coupling between this vector with the derivative of the field in higher order. The modification of the Klein&ndash;Gordon equation produces important corrections on the Casimir energy and pressure. Thus, we show that these corrections strongly depend on the order of the higher derivative term and the specific direction of the constant vector, as well as the boundary conditions considered.

]]>Universe doi: 10.3390/universe9050240

Authors: Sara Cruz-Barrios Guillermo D. Megias Juan A. Caballero

A systematic analysis of the weak responses for charged-current quasielastic neutrino-nucleus reactions is presented within the scheme of a fully relativistic microscopic model considering momentum-dependent scalar and vector mean field potentials in both the initial and final nucleon states. The responses obtained are compared with the ones corresponding to simpler approaches: energy-independent potentials and the relativistic plane wave limit in the final state, i.e., no potentials applied to the outgoing particle. The analysis is also extended to the scaling phenomenon, which provides additional information regarding nuclear dynamics. Results for the scaling function are shown for various nuclei and different values of the transferred momentum in order to analyze the behavior of the relativistic scalar and vector mean field potentials.

]]>Universe doi: 10.3390/universe9050239

Authors: Bhavika M. Patel Niraj M. Pathak Elbaz I. Abouelmagd

In this work, the perturbed equations of motion of the infinitesimal body are constructed in the framework of the circular restricted three-body problem when the main two bodies are oblate and radiating. Under the perturbations effects of the oblateness and the radiation pressure the positions of collinear Lagrange points are evaluated, the interior and exterior first-order resonant periodic orbits are also studied. In addition, the initial positions of the periodic orbits and the size of loops have been estimated under these effects. Thus, the characteristics of periodic orbits have been studied under the combine effects of two, three and four perturbations for all the possible combinations of the perturbed parameters. The different order of resonant periodic orbits have been also analysed under the effects of Jacobi constant, mass factor, order of resonance and number of loops.

]]>Universe doi: 10.3390/universe9050238

Authors: Julio Marny Hoff da Silva Rogerio Teixeira Cavalcanti

We investigate two physical systems within a spacetime region affected by the nontrivial topology. The set-up for our analysis is a Minkowski metric perturbed by elements reflecting the topological nontriviality. These elements arise when exploring Cartan&rsquo;s spinorial approach along with the exotic spinors counterpart. This evinced nontrivial topology corrections in the free particle dynamics and charged particles coupled to an external electromagnetic field. As a complement, we show the appearance of a magnetic monopole-like effect.

]]>Universe doi: 10.3390/universe9050237

Authors: Yu Chen Chang-Zhi Lu Juan Li Siqi Liu Tong-Jie Zhang Tingting Zhang

The study of massive neutrinos and their interactions is a critical aspect of contemporary cosmology. Recent advances in parallel computation and high-performance computing provide new opportunities for accurately constraining Large-Scale Structures (LSS). In this paper, we introduce the TianNu cosmological N-body simulation during the co-evolution of massive neutrino and cold dark matter components via the CUBEP3M code running on the supercomputer Tianhe-2 and TianNu&rsquo;s connected works. We start by analyzing 2.537&times;107 dark halos from the scientific data of TianNu simulation, and compare their angular momentum with the matched halos from neutrino-free TianZero, revealing a dependence of angular momentum modulus on neutrino injection at scales below 50 Mpc and around 10 Mpc.

]]>Universe doi: 10.3390/universe9050236

Authors: Ed Bennett Jack Holligan Deog Ki Hong Ho Hsiao Jong-Wan Lee C.-J. David Lin Biagio Lucini Michele Mesiti Maurizio Piai Davide Vadacchino

We review the current status of the long-term programme of numerical investigation of Sp(2N) gauge theories with and without fermionic matter content. We start by introducing the phenomenological as well as theoretical motivations for this research programme, which are related to composite Higgs models, models of partial top compositeness, dark matter models, and in general to the physics of strongly coupled theories and their approach to the large-N limit. We summarise the results of lattice studies conducted so far in the Sp(2N) Yang&ndash;Mills theories, measuring the string tension, the mass spectrum of glueballs and the topological susceptibility, and discuss their large-N extrapolation. We then focus our discussion on Sp(4), and summarise the numerical measurements of mass and decay constant of mesons in the theories with fermion matter in either the fundamental or the antisymmetric representation, first in the quenched approximation, and then with dynamical fermions. We finally discuss the case of dynamical fermions in mixed representations, and exotic composite fermion states such as the chimera baryons. We conclude by sketching the future stages of the programme. We also describe our approach to open access.

]]>Universe doi: 10.3390/universe9050235

Authors: Che-Jui Chang Jean-Fu Kiang

Strong &gamma;-ray outbursts have been observed to emanate from PKS 1502+106, followed by highly variable fluxes in radio, visual, ultraviolet and X-ray bands. Numerical simulations have been conducted to relate the observations to potential theoretical models. The plasma attributes, such as mass density, plasma flow velocity and energy density, cannot be directly observed. However, the Stokes parameters of synchrotron radiation from the plasma can be measured to deduce the plasma attributes. Many studies have been conducted on synchrotron radiation intensity, with only a few on the rotation measure (RM) related to Faraday rotation. In this work, overpressured relativistic magnetized axisymmetric jets are simulated to acquire the synchrotron radiation maps, incorporating Faraday rotation, of the widely discussed jet, PKS 1502+106. The intensity maps and RM maps of the PKS 1502+106 are simulated under practical constraints, and compared with the available observation data to explore specific features of the jet. The simulated intensity maps match well with the observation data in size and shape. The observed spine&ndash;sheath polarization structure, sign change in the RM slice and opposite RM gradients have been reproduced. The conjecture of helical magnetic field morphology in the literature has also been validated by comparing the simulation results under different magnetic field morphologies.

]]>Universe doi: 10.3390/universe9050234

Authors: Konstantin G. Zloshchastiev

Within the frameworks of the logarithmic superfluid model of physical vacuum, we demonstrate the emergence of four-dimensional curved spacetime from the dynamics of quantum Bose liquid in three-dimensional Euclidean space. We derive the metric tensor of this spacetime and study its special cases and limits, such as the linear-phase flow and linearized gravity limit. We show that the value of speed of light, which is a fundamental parameter in a theory of relativity, is a derived notion in superfluid vacuum theory: its value is a combination of the Planck constant and original parameters of the background superfluid. As for the gravitational potential, then it can be defined in terms of the quantum information entropy of the background superfluid. Thus, relativistic gravity and curved spacetime are shown to result from the dynamics of quantum excitations of the background superfluid being projected onto the measurement apparatus of a relativistic observer.

]]>Universe doi: 10.3390/universe9050233

Authors: Tamás Sándor Biró Norbert Kroó László Pál Csernai Miklós Veres Márk Aladi István Papp Miklós Ákos Kedves Judit Kámán Ágnes Nagyné Nagyné Szokol Roman Holomb István Rigó Attila Bonyár Alexandra Borók Shireen Zangana Rebeka Kovács Nóra Tarpataki Mária Csete András Szenes Dávid Vass Emese Tóth Gábor Galbács Melinda Szalóki

A status report is presented about the Nanoplasmonic Laser Induced Fusion Experiment (NAPLIFE). The goal is to investigate and verify plasmonically enhanced phenomena on the surfaces of nanoantennas embedded in a polymer target at laser intensities up to a few times 1016 W/cm2 and pulse durations of 40&ndash;120 fs. The first results on enhanced crater formation for Au-doped polymer targets are shown, and SERS signals typical for CD2 and ND bound vibrations are cited. Trials to detect D/H ratio by means of LIBS measurments are reported. Plasmonics has the potential to work at these intensities, enhancing the energy and deuterium production, due to thus far unknown mechanisms.

]]>Universe doi: 10.3390/universe9050232

Authors: Alexandre Landry Robert J. van den Hoogen

A complete perturbation theory suitable for teleparallel gravity is developed. The proposed perturbation scheme takes into account perturbations of the coframe, the metric, and the spin-connection, while ensuring that the resulting perturbed system continues to describe a teleparallel gravity situation. The resulting perturbation scheme can be transformed to one in which perturbations all take place within the co-frame. A covariant definition of a teleparallel Minkowski geometry is proposed. We compute the perturbed field equations for&nbsp;f(T)&nbsp;teleparallel gravity and discuss the stability of the teleparallel Minkowski geometry within&nbsp;f(T)&nbsp;teleparallel gravity.

]]>Universe doi: 10.3390/universe9050231

Authors: Igor Frolov Albert Schwarz

In quantum mechanics, one can express the evolution operator and other quantities in terms of functional integrals. The main goal of this paper is to prove corresponding results in geometric approach to quantum theory. We apply these results to the formalism of L-functionals.

]]>Universe doi: 10.3390/universe9050230

Authors: Jian Lian Tianyu Liu Yanan Zhou

An aurora is a unique geophysical phenomenon with polar characteristics that can be directly observed with the naked eye. It is the most concentrated manifestation of solar&ndash;terrestrial physical processes (especially magnetospheric&ndash;ionospheric interactions) in polar regions and is also the best window for studying solar storms. Due to the rich morphological information in aurora images, people are paying more and more attention to studying aurora phenomena from the perspective of images. Recently, some machine learning and deep learning methods have been applied to this field and have achieved preliminary results. However, due to the limitations of these learning models, they still need to meet the requirements for the classification and prediction of auroral images regarding recognition accuracy. In order to solve this problem, this study introduces a convolutional neural network transformer solution based on vision transformers. Comparative experiments show that the proposed method can effectively improve the accuracy of aurora image classification, and its performance has exceeded that of state-of-the-art deep learning methods. The experimental results show that the algorithm presented in this study is an effective instrument for classifying auroral images and can provide practical assistance for related research.

]]>Universe doi: 10.3390/universe9050229

Authors: Jingming Lu Yaogai Hu Chunhua Jiang Zhengyu Zhao Yuannong Zhang Zhengzheng Ma

The electron density (Ne), ion density (Ni), and electron temperature (Te) statistics recorded by the DEMETER satellite payload ISL (Instrument Sonde de Langmuir) were used to study the disturbance characteristics of the ionosphere before solid earthquakes of magnitude 6 or higher in Japan during the summer of 2005&ndash;2009, to provide more information and methods for the coupling mechanism and short-range earthquake prediction. In this paper, the region of &plusmn;10&deg; of the epicenter is divided into 1&deg;&times;1&deg; pixels, and the background field of each parameter is constructed using data without earthquakes and relatively calm space weather. We also define a measure of the perturbation intensity of ionospheric parameters relative to the background field during the occurrence of earthquakes. The analysis results of the four Japanese earthquakes from space and time show an excellent synchronization in the time and area of the anomalies in ionospheric parameters of the four cases. All four instances showed Ne abnormalities, and three showed Ni and Te anomalies, in which Ne and Ni increased or decreased abnormally, while Te increased abnormally every time, and the anomalies mainly occurred about 9&ndash;12 days before the earthquake. This paper eliminates the influence of solar, geomagnetic, and satellite data defects on the experimental results as much as possible in data screening and method selection. The results partially agree with the conclusions reported in the existing literature, and the obtained anomalies are somewhat related to the ionospheric precursors of earthquakes.

]]>Universe doi: 10.3390/universe9050228

Authors: Ivan Arraut Carlos Segovia Wilson Rosado

We prove the consistency of the different approaches for deriving the black hole radiation for the spherically symmetric case inside the theory of Massive Gravity. By comparing the results obtained by using the Bogoliubov transformations with those obtained by using the Path Integral formulation, we find that in both cases, the presence of the extra-degrees of freedom creates the effect of extra-particles creation due to the distortions on the definitions of time defined by the different observers at large scales. This, however, does not mean extra-particle creation at the horizon level. Instead, the apparent additional particles perceived at large scales emerge from how distant observers define their time coordinate, which is distorted due to the existence of extra-degrees of freedom.

]]>Universe doi: 10.3390/universe9050227

Authors: Ming Zhong Liyun Zhang Zilu Yang Tianhao Su

The investigation of the magnetic activity of different types of variable stars holds significant implications for our understanding of the physical processes and evolution of stars. This study&rsquo;s International Variable Star Index (VSX) variable star catalog was cross-matched with Transiting Exoplanet Survey Satellite (TESS) data, resulting in 26,276 labeled targets from 76,187 light curves. A total of 25,327 stellar flare events were detected, including 245 eclipsing binaries, 2324 rotating stars, 111 pulsating stars, and 629 eruptive stars. The results showed that flares from eclipsing binaries, rotating stars, eruptive stars, and pulsating stars have durations such that 90% are less than 2 h, and 91% of their amplitudes are less than 0.3. Flare events mainly occurred in the temperature range of 2000 K to 3000 K. The power-law indices of different types of variable stars were 1.72&plusmn;0.025 (eclipsing binaries), 1.82&plusmn;0.062 (rotating stars), 1.80&plusmn;0.0116 (eruptive stars), and 1.73&plusmn;0.060 (pulsating stars). Among them, the flare energy of pulsating stars is more concentrated in the high-energy range. In all samples, flare energies were distributed from 3.99&times;1031 erg to 6.18&times;1038 erg. The LAMOST DR9 low-resolution spectral survey has provided H&alpha; equivalent widths for 398 variable stars. By utilizing these H&alpha; equivalent widths, we have determined the stellar activity of the variable stars and confirmed a positive correlation between the flare energy and H&alpha; equivalent width.

]]>Universe doi: 10.3390/universe9050225

Authors: Mert Mangut Huriye Gürsel Sara Kanzi İzzet Sakallı

The ability of bumblebee gravity models to explain dark energy, which is the phenomenon responsible for the universe&rsquo;s observed accelerated expansion, is one of their most significant applications. An effect that causes faster expansion can be linked to how much the Lorentz symmetry of our universe is violated. Moreover, since we do not know what generates dark energy, the bumblebee gravity theory seems highly plausible. By utilizing the physical changes happening around a rotating bumblebee black hole (RBBH), we aim to obtain more specific details about the bumblebee black hole&rsquo;s spacetime and our universe. However, as researched in the literature, slow-spinning RBBH (SRBBH) spacetime, which has a higher accuracy, will be considered instead of general RBBH. To this end, we first employ the Rindler&ndash;Ishak method (RIM), which enables us to study how light is bent in the vicinity of a gravitational lens. We evaluate the deflection angle of null geodesics in the equatorial plane of the SRBBH spacetime. Then, we use astrophysical data to see the effect of the Lorentz symmetry breaking (LSB) parameter on the bending angle of light for numerous astrophysical stars and black holes. We also acquire the analytical greybody factors (GFs) and quasinormal modes (QNMs) of the SRBBH. Finally, we visualize and discuss the results obtained in the conclusion section.

]]>Universe doi: 10.3390/universe9050226

Authors: Fabian Gittins Thomas Celora Aru Beri Nils Andersson

We revisit the calculation of mode oscillations in the ocean of a rotating neutron star, which may be excited during thermonuclear X-ray bursts. Our present theoretical understanding of ocean modes relies heavily on the traditional approximation commonly employed in geophysics. The approximation elegantly decouples the radial and angular sectors of the perturbation problem by neglecting the vertical contribution from the Coriolis force. However, as the implicit assumptions underlying it are not as well understood as they ought to be, we examine the traditional approximation and discuss the associated mode solutions. The results demonstrate that, while the approximation may be appropriate in certain contexts, it may not be accurate for rapidly rotating neutron stars. In addition, using the shallow-water approximation, we show analytically how the solutions that resemble r-modes change their nature in neutron-star oceans to behave like gravity waves. We also outline a simple prescription for lifting Newtonian results in a shallow ocean to general relativity, making the result more realistic.

]]>Universe doi: 10.3390/universe9050224

Authors: Motshidisi Charity Sebogodi Ben Muatjetjeja Abdullahi Rashid Adem

This paper aims to analyze a generalized Chaffee&ndash;Infante equation with power-law nonlinearity in (1+3) dimensions. Ansatz methods are utilized to provide topological and non-topological soliton solutions. Soliton solutions to nonlinear evolution equations have several practical applications, including plasma physics and the diffusion process, which is why they are becoming important. Additionally, it is shown that for certain values of the parameters, the power-law nonlinearity Chaffee&ndash;Infante equation allows solitons solutions. The requirements and restrictions for soliton solutions are also mentioned. Conservation laws are derived for the aforementioned equation. In order to comprehend the dynamics of the underlying model, we graphically show the secured findings. Hirota&rsquo;s perturbation method is included in the multiple exp-function technique that results in multiple wave solutions that contain new general wave frequencies and phase shifts.

]]>Universe doi: 10.3390/universe9050223

Authors: Joshua Baines Matt Visser

Thanks to the recent advent of the event horizon telescope (EHT), we now have the opportunity to test the physical ramifications of the strong-field near-horizon regime for astrophysical black holes. Herein, emphasizing the trade-off between tractability and generality, the authors discuss a particularly powerful three-function distortion of the Kerr spacetime, depending on three arbitrary functions of the radial coordinate r, which on the one hand can be fit to future observational data, and on the other hand is sufficiently general so as to encompass an extremely wide class of theoretical models. In all of these spacetimes, both the timelike Hamilton&ndash;Jacobi (geodesic) and massive Klein&ndash;Gordon (wave) equations separate, and the spacetime geometry is asymptotically Kerr; hence, these spacetimes are well-suited to modeling real astrophysical black holes. The authors then prove the existence of Killing horizons for this entire class of spacetimes, and give tractable expressions for the angular velocities, areas, and surface gravities of these horizons. We emphasize the validity of rigidity results and zeroth laws for these horizons.

]]>Universe doi: 10.3390/universe9050222

Authors: Ivan Todorov

This paper surveys recent progress in our search for an appropriate internal space algebra for the standard model (SM) of particle physics. After a brief review of the existing approaches, we start with the Clifford algebras involving operators of left multiplication by octonions. A central role is played by a distinguished complex structure that implements the splitting of the octonions O=C&oplus;C3, which reflect the lepton-quark symmetry. Such a complex structure on the 32-dimensional space S of C&#8467;10 Majorana spinors is generated by the C&#8467;6(&sub;C&#8467;10) volume form, &omega;6=&gamma;1&#8943;&gamma;6, and is left invariant by the Pati&ndash;Salam subgroup of Spin(10), GPS=Spin(4)&times;Spin(6)/Z2. While the Spin(10) invariant volume form &omega;10=&gamma;1&hellip;&gamma;10 of C&#8467;10 is known to split S on a complex basis into left and right chiral (semi)spinors, P=12(1&minus;i&omega;6) is interpreted as the projector on the 16-dimensional particle subspace (which annihilates the antiparticles).The standard model gauge group appears as the subgroup of GPS that preserves the sterile neutrino (which is identified with the Fock vacuum). The Z2-graded internal space algebra A is then included in the projected tensor product A&sub;PC&#8467;10P=C&#8467;4&otimes;C&#8467;60. The Higgs field appears as the scalar term of a superconnection, an element of the odd part C&#8467;41 of the first factor. The fact that the projection of C&#8467;10 only involves the even part C&#8467;60 of the second factor guarantees that the color symmetry remains unbroken. As an application, we express the ratio mHmW of the Higgs to the W boson masses in terms of the cosine of the theoretical Weinberg angle.

]]>Universe doi: 10.3390/universe9050221

Authors: Qihong Huang Kaituo Zhang He Huang Bing Xu Feiquan Tu

The emergent universe provides a possible method to avoid the Big Bang singularity by considering that the universe stems from a stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in the CMB power spectrum. In this paper, we analyze the stability condition for the Einstein static universe in general relativity with k-essence against both the scalar and tensor perturbations. Furthermore, we find the emergent universe can be successfully realized by constructing a scalar potential and an equation of state parameter. Solving the curved Mukhanov&ndash;Sasaki equation, we obtain the analytical approximation for the primordial power spectrum, and then depict the TT-spectrum of the emergent universe. The results show that both the primordial power spectrum and CMB TT-spectrum are suppressed on large scales.

]]>Universe doi: 10.3390/universe9050220

Authors: Nikita A. Zemlyakov Andrey I. Chugunov

Neutron stars are the densest objects in the Universe. They have a microscopically homogeneous core and heterogeneous crust. In particular, there may be a specific layer inside neutron stars, the mantle, which consists of substantially non-spherical nuclei immersed in a background of relativistic degenerate electrons and quasi-free neutrons. In this paper, we reconsider the transverse shear modulus for cylindrical phases of the mantle within the framework of the compressible liquid drop model. We demonstrate that transverse shearing affects the shape of nuclear clusters: their cross-section becomes elliptical. This effect reduces the respective elastic constant. Using a simple model, we perform all derivations analytically and obtain the expression for the transverse shear modulus, which can be useful for astrophysical applications.

]]>Universe doi: 10.3390/universe9050219

Authors: Dmitry S. Kaparulin Nikita A. Sinelnikov

We consider the motion of a weakly relativistic charged particle with an arbitrary spin in central potential e/r in terms of classical mechanics. We show that the spin&ndash;orbital interaction causes the precession of the plane of orbit around the vector of total angular momentum. The angular velocity of precession depends on the distance of the particle from the centre. The effective potential for in-plane motion is central, with the corrections to Coulomb terms coming from spin&ndash;orbital interaction. The possible orbits of a quantum particle are determined by the Bohr&ndash;Sommerfeld quantization rule. We give examples of orbits corresponding to small quantum numbers, which were obtained by numerical integration of equations of motion. The energies of stationary states are determined by spin&ndash;orbital interaction.

]]>Universe doi: 10.3390/universe9050218

Authors: Peter J. Brown Macie Robertson Yaswant Devarakonda Emily Sarria David Pooley Maximilian D. Stritzinger

The Neil Gehrels Swift Observatory has proven to be an extraordinary supernova (SN) observatory. The clearest application of Swift&rsquo;s unique strengths is obtaining very early UV and X-ray data of young SNe, which enables robust constraints on their progenitor systems. As part of a year-long Swift Guest Investigator Key Project, we initiated a follow-up program to rapidly observe all of the nearest (distance &lt; 35 Mpc or roughly z &lt; 0.008) extragalactic transients without waiting for them to be spectroscopically classified as supernovae. Among the possible results were to measure any UV-bright radiative cooling following the shock breakout from core-collapse SNe and shock emission from the interaction of thermonuclear Type Ia SNe with a non-degenerate companion. Just as importantly, uniformly following up and analyzing a significant sample can constrain the fraction of events for which the shock emission is not seen. Here we present the UV and X-ray measurements performed during our campaign. Our sample of 24 observed triggers included three SNe Ia, six SNe II, three stripped-envelope, core-collapse SNe, five galactic transients, three extragalactic SN imposters, and four unconfirmed transients. For our sample, the median delay time from the discovery image to the first Swift image was 1.45 days. We tabulate the X-ray upper limits and find they are sufficiently deep to have detected objects as X-ray luminous as GRB060218/SN2006aj. Other X-ray-detected SNe such as SNe 2006bp, 2008D, and 2011dh would have been detectable in some of the observations. We highlight the spectroscopically classified Type II SN 2018hna with UV-optical light curves indicating a luminosity and flux evolution very similar to SN 1987A.

]]>Universe doi: 10.3390/universe9050217

Authors: Andrey A. Grib Yuri V. Pavlov

Particles with negative energies are considered for three different cases: inside the horizon of a Schwarzschild black hole, Milne&rsquo;s coordinates in flat Minkowski space&ndash;time (Milne&rsquo;s universe using nonsynchronous coordinates) and in the cosmological G&ouml;del model of the rotating universe. It is shown that, differently from the G&ouml;del model with a nondiagonal term, where it occurs that negative energies are impossible, they are present in all other cases considered in the paper. Particles with zero energy are also possible in the first two cases.

]]>Universe doi: 10.3390/universe9050216

Authors: Gang Deng Ye Xu Ling Pei Ni Hu Hongjing Xu

The Casimir force is calculated in the configuration of two parallel plates separated by an anisotropic media. The result exhibits a dependence on the orientation of the optical axis of the intervening media. It is possible that the Casimir force switches its direction as the optical axis orientation varies. The greatest magnitude of the force could be achieved at any optical axis orientation, depending on the dielectric properties of the plates and the intervening media. A comparison between the relativistic and nonrelativistic result revealed that the nonrelativistic approximation could significantly underestimate the attraction or overestimate the repulsion. This error was even greater when the optical axis of the intervening media was perpendicular to the surface of the plates. The nonrelativistic approximation might even fail to predict the trends of the Casimir force at small distances.

]]>Universe doi: 10.3390/universe9050215

Authors: Jun Xu Zongjun Ning Dong Li Fanpeng Shi

We have studied the quasi-periodic pulsations (QPPs) of the M2.3 flare that occurred in the active region NOAA 12172 on 23 September 2014. Through the fast Fourier transform (FFT) method, we decompose the flare light curves into fast- and slowly-varying components, and the cut-off threshold is 100 s. We find that the QPPs have a period of 40 s at soft X-ray (SXR), hard X-ray (HXR), radio and ultraviolet (UV). Based on the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), we find that the QPPs take place at the same time interval as the flare ribbon separation, and that the QPPs seem to originate from the flare ribbons. Our observations tend to support the mechanism of the periodic nonthermal electron injection during the flare eruption.

]]>Universe doi: 10.3390/universe9050214

Authors: Lijun Jia Zhuang Li Fei Wang

We propose to embed the General NMSSM (Next-to-Minimal Supersymmetric Standard Model) into the deflected AMSB (Anomaly Mediated Supersymmetry Breaking) mechanism with Yukawa/gauge deflection contributions. After the integration of the heavy messenger fields, the analytical expressions of the relevant soft SUSY breaking spectrum for General NMSSM at the messenger scale can be calculated. We find that successful EWSB (Electroweak Symmetry Breaking) and realistic low energy NMSSM spectrum can be obtained in some parameter regions. In addition, we find that the muon g&minus;2 anomaly and electron g&minus;2 anomaly (for positive central value electron g&minus;2 experimental data) can be jointly explained to 1&sigma; and 2&sigma; range, respectively. The Z3 invariant NMSSM, which corresponds to &xi;F=0 in our case, can also jointly explain the muon and electron anomaly to 1&sigma; and 2&sigma; range, respectively.

]]>Universe doi: 10.3390/universe9050213

Authors: Zhi-Yang Liu Wei-Guo Zong Qiu-Gang Zong Jin-Song Wang Xiang-Qian Yu Yong-Fu Wang Hong Zou Sui-Yan Fu Chao Yue Ze-Jun Hu Jian-Jun Liu

Alfven-branch waves provide an efficient means for transporting energy into the auroral oval. Here, we report observations of these waves obtained by the Fengyun-3E (FY-3E)/ACMag instruments, which are designed to detect three-dimensional AC magnetic fields in the 0.05&ndash;25 Hz band. The observations suggest that broadband waves are a permanent feature of the auroral oval, although their amplitude and locations vary with the global state of the magnetosphere. We primarily focus on the data obtained from 10 July 2021 to 26 August 2021, during which a series of recurrent storms driven by solar wind corotating interaction regions (CIRs) occurred. Analysis of the observations shows that the auroral-oval waves grow in amplitude (1&ndash;3 orders of magnitude) and shift to lower latitude (&sim;10&deg;) immediately following the decrease in the SYM-H index in each storm. Further investigation reveals the response of the auroral-oval waves has a time scale equal to or less than FY-3E&rsquo;s effective revisiting time, which is about 45 min. The observations presented in this paper confirm that the FY-3E/ACMag instruments provide a high-resolution monitor of the auroral-oval waves and could further our understanding of auroral physics.

]]>Universe doi: 10.3390/universe9050212

Authors: Elena Fedorova Antonio Del Popolo

The 3C120 (Mrk 1506, UGC 03087, Mrk 9014) is a type 1 Seyfert (Sy1)/broad-line radio galaxy (BLRG) with intriguing variable jet activity featuring &ldquo;dip&rdquo; and &ldquo;outburst&rdquo; phases. Significant X-ray observational datasets have been collected for 3C120 by INTEGRAL, XMM-Newton, SWIFT, Suzaku, and other X-ray observational facilities. The overall X-ray spectrum of 3C 120 is too soft for typical radio-loud AGN, likely due to both variable spectral shape and jet contamination. Separating the &ldquo;jet base&rdquo; and nuclear (disc/corona) counterparts in the X-ray spectrum of 3C 120 can provide us with the possibility to investigate its variability in a more detailed way. Our objectives are to estimate separately the time variations of the accretion disc/corona and SSC/IC jet emission counterparts in the 3C 120 X-ray spectra and to analyze the physical state of the nucleus during different phases. Here, we attempt to use the connections between the synchrotron radio- and X-ray SSC/IC jet spectra and their photon indices and the dependence between the nuclear continuum and Fe-K iron luminescent line emission near 6.4 keV to separate the nuclear and jet base contributions to the total X-ray continuum. Using the X-ray observational dataset of 3C 120, we obtained separated fluxes that were interpreted as originating from the nucleus (disc/corona) and non-thermal SSC/IC jet base contributions. After this component separation, we identified the accretion disc/corona and jet states during different phases and compared them with the &ldquo;jet/disk cycle&rdquo; (Lohfink) and &ldquo;magnetic plasmoid reconnection&rdquo; (Shukla/Manheim) models.

]]>Universe doi: 10.3390/universe9050211

Authors: Lorenzo Iorio

The new geodetic satellite LARES 2, cousin of LAGEOS and sharing with it almost the same orbital parameters apart from the inclination, displaced by 180 deg, was launched last year. Its proponents suggest using the sum of the nodes of LAGEOS and of LARES 2 to measure the sum of the Lense&ndash;Thirring node precessions independently of the systematic bias caused by the even zonal harmonics of the geopotential, claiming a final &#8771;0.2 percent total accuracy. In fact, the actual orbital configurations of the two satellites do not allow one to attain the sought for mutual cancellation of their classical node precessions due to the Earth&rsquo;s quadrupole mass moment, as their sum is still &#8771;5000 times larger than the added general relativistic rates. This has important consequences. One is that the current uncertainties in the eccentricities and the inclinations of both satellites do not presently allow the stated accuracy goal to be met, needing improvements of 3&ndash;4 orders of magnitude. Furthermore, the imperfect knowledge of the Earth&rsquo;s angular momentum S impacts the uncancelled sum of the node precessions, from 150 to 4900 percent of the relativistic signal depending on the uncertainty assumed in S. It is finally remarked that the real breakthrough in reliably testing the gravitomagnetic field of the Earth would consist in modeling it and simultaneously estimating one or more dedicated parameter(s) along with other ones characterising the geopotential, as is customarily performed for any other dynamical feature.

]]>Universe doi: 10.3390/universe9050210

Authors: Ilya Potravnov Tatiana Ryabchikova Svetlana Artemenko Maxim Eselevich

We present results of the investigation of the star LkH&alpha; 324/B, which belongs to the starforming dark cloud LDN 988. Based on high resolution spectroscopy, we determined its fundamental parameters as Teff=11,175&plusmn;130 K, log(L*/L&#8857;)=1.87&plusmn;0.07. According to these parameters, we found that LkH&alpha; 324/B is a pre-main sequence star with mass M&asymp;3M&#8857; and age t&asymp;2.9 Myr. Recently, it underwent the phase of actively accreting the Herbig Ae/Be star, but accretion has now ceased in the LkH&alpha; 324/B system. This is consistent with the fact that the star is surrounded by a circumstellar disk with an inner cavity, as was determined from its spectral energy distribution. Our analysis revealed the peculiar abundance pattern of LkH&alpha; 324/B typical to those of magnetic Ap stars. It possesses mild underabundance of the light elements and excess up to &sim;2&ndash;4 dex (in comparison to the Sun) of the iron peak and rare earth elements. We found no evidence for abrupt vertical abundances gradients in the lines forming the region of the LkH&alpha; 324/B atmosphere, in agreement with the results of the theoretical diffusion calculations in this temperature domain. From the intensification of the magnetically sensitive lines, we deduced that LkH&alpha; 324/B probably hosts a global magnetic field of &#10216;B&#10217;&asymp;3.5 kG strength. We suppose that the stabilizing role of this field favored the elements&rsquo; separation by diffusion before the star reached the main sequence.

]]>Universe doi: 10.3390/universe9050209

Authors: Gerald A. Miller

Nuclear super-allowed &beta; decay has been used to obtain tight limits on the value of the CKM matrix element Vud that is important for unitarity tests and, therefore, for tests of the standard model. Current requirements on precision are so intense that effects formerly thought too small to matter are now considered relevant. This article is a brief review of personal efforts to include the effects of strong interactions on Fermi &beta; decay. First, I examine the role of isospin violation in the decay of the neutron. The size of the necessary correction depends upon detailed strong-interaction dynamics. The isospin violating parts of the nucleon wave function, important at the low energy of &beta; decay, can be constrained by data taken at much higher energies, via measurements, for example, of ed&rarr;e&prime;&pi;&plusmn;+X reactions at Jefferson Laboratory. The next point of focus is on the role of nuclear short-ranged correlations, which affect the value of the correction needed to account for isospin violation in extracting the value of Vud. The net result is that effects previously considered as irrelevant are now considered relevant for both neutron and nuclear &beta; decay.

]]>Universe doi: 10.3390/universe9050208

Authors: M. K. Jasim Ksh. Newton Singh Abdelghani Errehymy S. K. Maurya M. V. Mandke

In the present paper, we focused on exploring the possibility of providing a new class of exact solutions for viable anisotropic stellar systems by means of the massive Brans&ndash;Dicke (BD) theory of gravity. In this respect, we used the decoupling of gravitational sources by minimal geometric deformation (MGD) (e&minus;&eta;=&Psi;+&beta;h) for compact stellar objects in the realm of embedding class-one space-time to study anisotropic solutions for matter sources through the modified Einstein field equations. For this purpose, we used the ansatz for &Psi; relating to the prominent, well-known and well-behaved Finch&ndash;Skea model via Karmarkar condition, and the determination scheme for deformation function h(r) was proposed via mimic requirement on radial pressure component: &theta;11(r)=pr(r) and matter density: &theta;00(r)=&rho;(r) for the anisotropic sector. Moreover, we analyzed the main physical highlights of the anisotropic celestial object by executing several physical tests for the case &theta;11(r)=pr(r). We have clearly shown how the parameters &alpha;, &beta; and &omega;BD introduced by massive BD gravity via the MGD approach incorporating the anisotropic profile of the matter distribution have an immense effect on many physical parameters of compact bodies such as LMC X-4, LMC X-4, Her X-1, 4U 1820-30, 4U 1608-52, SAX J1808.4&ndash;658 and many others that can be fitted.

]]>Universe doi: 10.3390/universe9050207

Authors: Nils Van Dessel Vishvas Pandey Heather Ray Natalie Jachowicz

The prospects of extracting new physics signals in coherent elastic neutrino&ndash;nucleus scattering (CE&nu;NS) processes are limited by the precision with which the underlying nuclear structure physics, embedded in the weak nuclear form factor, is known. We present calculations of charge and weak nuclear form factors and CE&nu;NS cross sections on 12C, 16O, 40Ar, 56Fe and 208Pb nuclei. We obtain the proton and neutron densities, and charge and weak form factors by solving Hartree&ndash;Fock (HF) equations with a Skyrme (SkE2) nuclear potential. We validate our approach by comparing 208Pb and 40Ar charge form factor predictions with available elastic electron scattering data. Since CE&nu;NS experiments at stopped-pion sources are also well suited to measure inelastic charged&ndash;current and neutral&ndash;current neutrino&ndash;nucleus cross sections, we also present calculations for these processes, incorporating a continuum Random Phase Approximation (CRPA) description on top of the HF&ndash;SkE2 picture of the nucleus. Providing both coherent as well as inelastic cross sections in a consistent framework, we aim at obtaining a reliable and detailed comparison of the strength of these processes in the energy region below 100 MeV. Furthermore, we attempt to gauge the level of theoretical uncertainty pertaining to the description of the 40Ar form factor and CE&nu;NS cross sections by comparing relative differences between recent microscopic nuclear theory and widely-used phenomenological form factor predictions. Future precision measurements of CE&nu;NS will potentially help in constraining these nuclear structure details that will in turn improve prospects of extracting new physics.

]]>Universe doi: 10.3390/universe9050206

Authors: Junping Yang Xiang Chen Ying Cui Zhuxia Li Yingxun Zhang

To improve the constraints of symmetry energy at subsaturation density, measuring and accumulating more neutron skin data for neutron-rich unstable nuclei is naturally required. Aiming to probe the neutron skin of unstable nuclei by using low-intermediate-energy heavy-ion collisions, we develop a new version of an improved quantum molecular dynamics model, in which the neutron skin of the initial nucleus and the mean-field potential in nucleon propagation are consistently treated. Our calculations show that the three observables, such as the cross-sections of the primary projectile-like residues with A&gt;100 (&sigma;A&gt;100), the difference of &sigma;A&gt;100 between 132Sn + 124Sn and 124Sn + 124Sn systems (&delta;&sigma;A&gt;100), and the neutron-to-proton yield ratio (R(n/p)) in the transverse direction, could be used to measure the neutron skin of the unstable nuclei and to constrain the slope of the symmetry energy in the future.

]]>Universe doi: 10.3390/universe9050205

Authors: Horacio S. Vieira

We examine the interaction between quantum test particles and the gravitational field generated by a black hole solution that was recently obtained in the consistent 4-dimensional Einstein&ndash;Gauss&ndash;Bonnet gravity. While quasinormal modes of scalar, electromagnetic, and Dirac fields have been recently studied in this theory, there is no such study for the quasibound states. Here, we calculate the spectrum of quasibound states for the test fields in a spherically symmetric and asymptotically flat black hole solution in the consistent 4-dimensional Einstein&ndash;Gauss&ndash;Bonnet gravity. The quasispectrum of resonant frequencies is obtained by using the polynomial condition associated to the general Heun functions. We also discuss the stability of the systems for some values of the Gauss-Bonnet coupling constant.

]]>Universe doi: 10.3390/universe9050204

Authors: Vladimir N. Yershov

Einstein&ndash;Newcomb&ndash;de Sitter (ENdS) space is de Sitter&rsquo;s modification of spherical space used by Einstein in his first cosmological model paper published in 1917. The modification by de Sitter incorporated the topological identification of antipodal points in space previously proposed by Newcomb in 1877. De Sitter showed that space topologically modified in this way (called elliptical or projective space) satisfies Einstein&rsquo;s field equations. De Sitter also found that in a space with constant positive curvature, spectral lines of remote galaxies would be red-shifted (called the de Sitter effect). However, de Sitter&rsquo;s formulae relating distances to red shifts do not satisfy observational data. The likely reason for this mismatch is that de Sitter mainly focused on space curvature and ignored the identification of antipodal points. Herein, we demonstrate that it is this particular feature that allows an almost perfect fit of the ENdS-based cosmological model to observational data. We use 1701 sources from the type Ia supernovae data sample called Pantheon+, which was previously used to fit the &Lambda;CDM model. &Lambda;CDM and ENdS diverge in their predictions for red shifts exceeding z&sim;2.3. Since there are no available type Ia supernovae (SNe) data for higher red shifts, both models can be validated by using an additional sample of 193 gamma-ray bursts (GRBs) spanning red shifts up to z&sim;8. This validation shows that the minimum &chi;2 for the SNe+GRBs sample is about 2.7% smaller for the ENdS space model than for the &Lambda;CDM model.

]]>Universe doi: 10.3390/universe9050203

Authors: Ogan Özsoy Gianmassimo Tasinato

We review conceptual aspects of inflationary scenarios able to produce primordial black holes by amplifying the size of curvature fluctuations to the level required to trigger black hole formation. We identify general mechanisms to do so, both for single- and multiple-field inflation. In single-field inflation, the spectrum of curvature fluctuations is enhanced by pronounced gradients of background quantities controlling the cosmological dynamics, which can induce brief phases of non-slow-roll inflationary evolution. In multiple-field inflation, the amplification occurs through appropriate couplings with additional sectors characterized by tachyonic instabilities that enhance the size of their fluctuations. As representative examples, we consider axion inflation and two-field models of inflation with rapid turns in field space. We develop our discussion in a pedagogical manner by including some of the most relevant calculations and by guiding the reader through the existing theoretical literature, emphasizing general themes common to several models.

]]>Universe doi: 10.3390/universe9050202

Authors: Shuhua Yang Chunmei Pi Xiaoping Zheng Fridolin Weber

Strange stars ought to exist in the universe according to the strange quark matter hypothesis, which states that matter made of roughly equal numbers of up, down, and strange quarks could be the true ground state of baryonic matter rather than ordinary atomic nuclei. Theoretical models of strange quark matter, such as the standard MIT bag model, the density-dependent quark mass model, or the quasi-particle model, however, appear to be unable to reproduce some of the properties (masses, radii, and tidal deformabilities) of recently observed compact stars. This is different if alternative gravity theory (e.g., non-Newtonian gravity) or dark matter (e.g., mirror dark matter) are considered, which resolve these issues. The possible existence of strange stars could thus provide a clue to new physics, as discussed in this review.

]]>Universe doi: 10.3390/universe9050201

Authors: Han Lin Jujia Zhang Xinghan Zhang

Type II supernovae (SNe II), which show abundant hydrogen in their spectra, belong to a class of SNe with diverse observed properties. It is commonly accepted that SNe II are produced by core collapse and explosion of massive stars. However, the large photometric and spectroscopic diversity of SNe II and the mechanisms responsible for this diversity are not thoroughly understood. In this review, we first briefly introduce the optical characteristics and possible progenitors of each subtype of SNe II. We then highlight the role of the Chinese Space Station Telescope in future SN studies. With a deep limiting magnitude, the main survey project could detect SN IIP-like objects as distant as z&sim;1.2 and obtain UV-optical follow-up for peculiar transients, especially those long-lived events. With a high resolution and a large field of view, the main survey camera is powerful in linking a nearby SN with its progenitor, while the integral field spectrograph is powerful in revealing the SN environment. All this information has the potential to help enrich our understanding of supernova physics.

]]>Universe doi: 10.3390/universe9050200

Authors: Margherita Grespan Marek Biesiada

The first successful detection of gravitational waves (GWs) opened up a new window to study a realm of the most violent phenomena in the universe, such as coalescences of binary black holes (BH&ndash;BH), binary neutron stars (NS&ndash;NS), and mixed (BH&ndash;NS) systems, which are mostly inaccessible in the electromagnetic window. On the other hand, strong gravitational lensing of distant sources, such as galaxies and quasars, by other massive objects lying closer along the line of sight has become a powerful tool in cosmology and astrophysics. With the increasing sensitivity of the new generation of GW detectors, the chances to detect a strongly lensed GW signal are increasing. When GWs are strongly lensed, magnification of the signal intensity is expected, unveiling binary compact objects otherwise too distant to be detected. Such systems are important for their plethora of applications. Lensed GWs can be a test for general relativity, constrain mass distribution in galaxies or galaxy clusters, and provide cosmography information independently of the local cosmic ladders. In this review, we will provide a theoretical background of the gravitational lensing of GWs, including the wave optics regime, which becomes important in this context. Then we will describe the possible cosmological and astrophysical insight hidden in these signals, and present the state-of-the-art searches of lensed GWs in the present and future GW observatories.

]]>Universe doi: 10.3390/universe9040199

Authors: Adam Z. Kaczmarek Dominik Szczȩśniak Sabre Kais

We present a systematic and complementary study of quantum correlations near a black hole by considering measurement-induced nonlocality (MIN). The quantum measure of interest is discussed for the fermionic, bosonic and mixed fermion&ndash;boson modes on equal footing with respect to the Hawking radiation. The obtained results show that in the infinite Hawking temperature limit, the physically accessible correlations do not vanish only in the fermionic case. However, the higher frequency modes can sustain correlations for the finite Hawking temperature, with mixed systems being more sensitive towards the increase in the fermionic frequencies than the bosonic ones. Since the MIN for the latter modes quickly diminishes, the increased frequency may be a way to maintain nonlocal correlations for the scenarios at the finite Hawking temperature.

]]>Universe doi: 10.3390/universe9040198

Authors: Nicoleta Voicu Annamária Friedl-Szász Elena Popovici-Popescu Christian Pfeifer

For the general class of pseudo-Finsler spaces with (&alpha;,&beta;)-metrics, we establish necessary and sufficient conditions such that these admit a Finsler spacetime structure. This means that the fundamental tensor has a Lorentzian signature on a conic subbundle of the tangent bundle and thus the existence of a cone of future-pointing time-like vectors is ensured. The identified (&alpha;,&beta;)-Finsler spacetimes are candidates for applications in gravitational physics. Moreover, we completely determine the relation between the isometries of an (&alpha;,&beta;)-metric and the isometries of the underlying pseudo-Riemannian metric a; in particular, we list all (&alpha;,&beta;)-metrics which admit isometries that are not isometries of a.

]]>Universe doi: 10.3390/universe9040197

Authors: C. R. Argüelles E. A. Becerra-Vergara J. A. Rueda R. Ruffini

The nature of dark matter (DM) is one of the most relevant questions in modern astrophysics. We present a brief overview of recent results that inquire into the possible fermionic quantum nature of the DM particles, focusing mainly on the interconnection between the microphysics of the neutral fermions and the macrophysical structure of galactic halos, including their formation both in the linear and non-linear cosmological regimes. We discuss the general relativistic Ruffini&ndash;Arg&uuml;elles&ndash;Rueda (RAR) model of fermionic DM in galaxies, its applications to the Milky Way, the possibility that the Galactic center harbors a DM core instead of a supermassive black hole (SMBH), the S-cluster stellar orbits with an in-depth analysis of the S2&rsquo;s orbit including precession, the application of the RAR model to other galaxy types (dwarf, elliptic, big elliptic, and galaxy clusters), and universal galaxy relations. All the above focus on the model parameters&rsquo; constraints most relevant to the fermion mass. We also connect the RAR model fermions with particle physics DM candidates, self-interactions, and galactic observable constraints. The formation and stability of core&ndash;halo galactic structures predicted by the RAR model and their relations to warm DM cosmologies are also addressed. Finally, we provide a brief discussion of how gravitational lensing, dynamical friction, and the formation of SMBHs can also probe the DM&rsquo;s nature.

]]>Universe doi: 10.3390/universe9040196

Authors: Thomas W. Donnelly

High-energy lepton scattering constitutes the focus of this study. Developments are provided to motivate the basic choices of kinematic variables for the particular case of semi-inclusive electron scattering where these variables are devised to match well with the underlying dynamics to be expected for the general &ldquo;nuclear landscape&rdquo;. Various nuclear structure issues and other issues related to the nature of the electroweak currents at high energies are then discussed, as are some of the issues related to the different conditions occurring for electron scattering versus what is typically the case for charge-changing neutrino reactions.

]]>Universe doi: 10.3390/universe9040195

Authors: Mikhail Aleksandrovich Braun

Production of pions in high-energy collisions with nuclei in the kinematics prohibited for free nucleons (&ldquo;cumulative pions&rdquo;) is studied in the fusing color string model. The model describes the so-called direct mechanism for cumulative production. The other (spectator) mechanism dominates in production of cumulative protons, and is suppressed for pions. In the model, cumulative pions are generated by string fusion, which raises the maximal energy of produced partons above the level of the free nucleon kinematics. Momentum and multiplicity sum rules are used to determine the spectra in the deep fragmentation region. Predicted spectra of cumulative pions exponentially fall with the scaling variable x in the interval 1&lt;x&lt;3 with a slope between 5.1 and 5.6, which agrees well with the raw data obtained in the recent experiment at RHIC involving Cu&ndash;Au collisioins. However, the agreement is worse for the so-called unfolded data, presumably taking into account corrections due to the experimental setup and having rather a power-like form.

]]>Universe doi: 10.3390/universe9040194

Authors: Enrique Gaztanaga

In a paper published in 1939, Albert Einstein argued that Black Holes (BHs) did not exist &ldquo;in the real world&rdquo;. However, recent astronomical observations indicate otherwise. Does this mean that we should also expect White Holes (WHs) to exist in the real world? In classical General Relativity (GR), a WH refers to the time reversed version of a collapsing BH solution that allows the crossing of the BH event horizon inside out. Such solution has been disputed as not possible because escaping an event horizon violates causality. Despite such objections, the Big Bang model is often understood as a WH (the reverse of a BH collapse). Does this mean that the Big Bang breaks causality? Recent measurements of cosmic acceleration indicate that our Big Bang solution is not really a WH, but a BH. Events decelerate when the expansion accelerates and this prevents the crossing of the event horizon from inside out. We present a general explanation of why this happens; the explanation resolves the above causality puzzle and indicates that such apparent WH solutions have a regular Schwarzschild BH exterior.

]]>Universe doi: 10.3390/universe9040193

Authors: Sheng-Quan Wang Stanley J. Brodsky Xing-Gang Wu Jian-Ming Shen Leonardo Di Giustino

The setting of the renormalization scale (&mu;r) in the perturbative QCD (pQCD) is one of the crucial problems for achieving precise fixed-order pQCD predictions. The conventional prescription is to take its value as the typical momentum transfer Q in a given process, and theoretical uncertainties are then evaluated by varying it over an arbitrary range. The conventional scale-setting procedure introduces arbitrary scheme-and-scale ambiguities in fixed-order pQCD predictions. The principle of maximum conformality (PMC) provides a systematic way to eliminate the renormalization scheme-and-scale ambiguities. The PMC method has rigorous theoretical foundations; it satisfies the renormalization group invariance (RGI) and all of the self-consistency conditions derived from the renormalization group. The PMC has now been successfully applied to many physical processes. In this paper, we summarize recent PMC applications, including event shape observables and heavy quark pair production near the threshold region in e+e&minus; annihilation and top-quark decay at hadronic colliders. In addition, estimating the contributions related to the uncalculated higher-order terms is also summarized. These results show that the major theoretical uncertainties caused by different choices of &mu;r are eliminated, and the improved pQCD predictions are thus obtained, demonstrating the generality and applicability of the PMC.

]]>Universe doi: 10.3390/universe9040192

Authors: Yuanqing Fang Bo Ma Chen Chen Yongxin Wen

The characterization of young planet distribution is essential for our understanding of the early evolution of exoplanets. Here we conduct a systematic search for young planets from young open clusters and associations using the 2-min cadence TESS survey data. We obtain TESS light curves for a total of 1075 young stars, which are selected with the aid of Gaia data. There are a total of 16 possible transiting signals. After a thorough vetting process, some have been confirmed as planets, and others are likely caused by eclipsing binaries. The final sample contains six confirmed planets, of which one is a hot Jupiter. After accounting for survey completeness using a Monte Carlo simulation, we can put a 95% confidence level upper limit on the hot Jupiter (P &lt; 10 days, Rp = 0.7&ndash;2.9 RJup) occurrence rate orbiting stars in young associations at &lt;5.1% and a 68% confidence level upper limit at &lt;2.5%. We estimate that a sample size of &sim;5000 dwarf stars with 2-min cadence data will be needed to reach a 0.5% upper limit on the hot Jupiter occurrence rate, which is the typical hot Jupiter occurrence rate around main sequence stars. Thus, future studies with larger sample sizes are required to put more constraints on planet formation and evolution theories.

]]>Universe doi: 10.3390/universe9040191

Authors: A. K. Rao R. P. Malik

We demonstrate that the celebrated St&uuml;ckelberg formalism is modified in the case of a massive four (3 + 1)-dimensional (4D) Abelian 2-form theory due to the presence of a self-duality discrete symmetry in the theory. The latter symmetry entails upon the modified 4D massive Abelian 2-form gauge theory to become a massive model of Hodge theory within the framework of Becchi&ndash;Rouet&ndash;Stora&ndash;Tyutin (BRST) formalism where there is the existence of a set of (anti-)co-BRST transformations corresponding to the usual nilpotent (anti-)BRST transformations. The latter exist in any arbitrary dimension of spacetime for the usual St&uuml;ckelberg-modified massive Abelian 2-form gauge theory. The modification in the St&uuml;ckelberg technique is backed by the precise mathematical arguments from the differential geometry where the exterior derivative and Hodge duality operator play the decisive roles. The modified version of the St&uuml;ckelberg technique remains invariant under the discrete duality transformations which also establish a precise and deep connection between the off-shell nilpotent (anti-)BRST and (anti-)co-BRST transformations. We have clarified a simple trick of using the equations of motion to remove the higher derivative terms in the appropriate Lagrangian densities so that our 4D theory can become consistent.

]]>Universe doi: 10.3390/universe9040190

Authors: Sanjar Shaymatov Bobomurat Ahmedov Eldor Karimbaev

Five-dimensional rotating black holes with two rotations could be overspun except for a single rotation, whereas a black hole in six dimensions always obeys the weak cosmic censorship conjecture (WCCC) in the weak form even for linear particle accretion. In this paper, we investigate the overspinning of a seven-dimensional rotating black hole with three rotation parameters. It is shown that a black hole in the seven dimensions cannot be similarly overspun, thereby obeying the WCCC even under linear particle accretion. It turns out that a black hole always respects the weak cosmic censorship conjecture in seven dimensions.

]]>Universe doi: 10.3390/universe9040189

Authors: Xiao-Yu Lu Jin-Shu Huang Cong-Bin Liu Xiu-Mei Xu Jin-Bing Cheng Wan Chang Yu-Yu Zhou Ya-Jie Wang

The clock comparison experiments to test special relativity mainly include the Michelson&ndash;Morley experiment, Kennedy&ndash;Thorndike experiment, Ives&ndash;Stilwell experiment and the comparison experiment of atomic clocks in two locations. These experiments can be roughly classified as the comparison of two types of clocks: optical clocks and atomic clocks. Through the comparison of such clocks, Lorentz invariance breaking parameters in the RMS framework can be tested. However, in such experiments, the structural effects of optical clocks have been fully considered, yet the structural effects of atomic clocks have not been carefully studied. Based on this, this paper analyzes the structural effects of atomic clocks in detail and divides the experiments into six types: the comparison of two atomic clocks, two optical clocks, and atomic clocks and optical clocks placed in different and the same locations. Finally, correction parameters for the experimental measurements are given.

]]>Universe doi: 10.3390/universe9040188

Authors: Marek Czachor

A new dynamical paradigm merging quantum dynamics with cosmology is discussed. We distinguish between a universe and its background space-time. The universe here is the subset of space-time defined by &Psi;&tau;(x)&ne;0, where &Psi;&tau;(x) is a solution of a Schr&ouml;dinger equation, x is a point in n-dimensional Minkowski space, and &tau;&ge;0 is a dimensionless &lsquo;cosmic-time&rsquo; evolution parameter. We derive the form of the Schr&ouml;dinger equation and show that an empty universe is described by a &Psi;&tau;(x) that propagates towards the future inside some future-cone V+. The resulting dynamical semigroup is unitary, i.e., &int;V+d4x|&Psi;&tau;(x)|2=1 for &tau;&ge;0. The initial condition &Psi;0(x) is not localized at x=0. Rather, it satisfies the boundary condition &Psi;0(x)=0 for x&notin;V+. For n=1+3 the support of &Psi;&tau;(x) is bounded from the past by the &lsquo;gap hyperboloid&rsquo; &#8467;2&tau;=c2t2&minus;x2, where &#8467; is a fundamental length. Consequently, the points located between the hyperboloid and the light cone c2t2&minus;x2=0 satisfy &Psi;&tau;(x)=0, and thus do not belong to the universe. As &tau; grows, the gap between the support of &Psi;&tau;(x) and the light cone increases. The past thus literally disappears. Unitarity of the dynamical semigroup implies that the universe becomes localized in a finite-thickness future-neighbourhood of &#8467;2&tau;=c2t2&minus;x2, simultaneously spreading along the hyperboloid. Effectively, for large &tau; the subset occupied by the universe resembles a part of the gap hyperboloid itself, but its thickness &Delta;&tau; is non-zero for finite &tau;. Finite &Delta;&tau; implies that the three-dimensional volume of the universe is finite as well. An approximate radius of the universe, r&tau;, grows with &tau; due to &Delta;&tau;r&tau;3=&Delta;0r03 and &Delta;&tau;&rarr;0. The propagation of &Psi;&tau;(x) through space-time matches an intuitive picture of the passage of time. What we regard as the Minkowski-space classical time can be identified with ct&tau;=&int;d4xx0|&Psi;&tau;(x)|2, so t&tau; grows with &tau; as a consequence of the Ehrenfest theorem, and its present uncertainty can be identified with the Planck time. Assuming that at present values of &tau; (corresponding to 13&ndash;14 billion years) &Delta;&tau; and r&tau; are of the order of the Planck length and the Hubble radius, we estimate that the analogous thickness &Delta;0 of the support of &Psi;0(x) is of the order of 1 AU, and r03&sim;(ctH)3&times;10&minus;44. The estimates imply that the initial volume of the universe was finite and its uncertainty in time was several minutes. Next, we generalize the formalism in a way that incorporates interactions with matter. We are guided by the correspondence principle with quantum mechanics, which should be asymptotically reconstructed for the present values of &tau;. We argue that Hamiltonians corresponding to the present values of &tau; approximately describe quantum mechanics in a conformally Minkowskian space-time. The conformal factor is directly related to |&Psi;&tau;(x)|2. As a by-product of the construction, we arrive at a new formulation of conformal invariance of m&ne;0 fields.

]]>Universe doi: 10.3390/universe9040187

Authors: Giampiero Esposito

DeWitt&rsquo;s suggestion that the wave function of the universe should vanish at the classical Big Bang singularity is considered here within the framework of one-loop quantum cosmology. For pure gravity at one loop about a flat four-dimensional background bounded by a 3-sphere, three choices of boundary conditions are considered: vanishing of the linearized magnetic curvature when only transverse-traceless gravitational modes are quantized; a one-parameter family of mixed boundary conditions for gravitational and ghost modes; and diffeomorphism-invariant boundary conditions for metric perturbations and ghost modes. A positive &zeta;(0) value in these cases ensures that, when the three-sphere boundary approaches zero, the resulting one-loop wave function approaches zero. This property may be interpreted by saying that, in the limit of small three-geometry, the resulting one-loop wave function describes a singularity-free universe. This property holds for one-loop functional integrals, which are not necessarily equivalent to solutions of the quantum constraint equations.

]]>Universe doi: 10.3390/universe9040186

Authors: Alessandro A. Quarta Giovanni Mengali

The recent discovery of Earth&rsquo;s second Trojan asteroid (2020 XL5), which will remain in the vicinity of the Sun&ndash;[Earth+Moon] triangular Lagrangian point L4 for at least 4000 years, has attracted the attention of the scientific community as a remarkable example of those elusive objects that are the witnesses of the first phase of our Solar System. The possibility that an Earth&rsquo;s Trojan asteroid (ETa) may represent a pristine record of the initial conditions of the Solar System formation makes these small objects an interesting target for a robotic exploration mission. This paper analyzes orbit-to-orbit Earth&ndash;ETa transfer trajectories of an interplanetary spacecraft propelled by a solar sail. In the last decade, some pioneering space missions have confirmed the feasibility and potentiality of the solar sail concept as a propellantless propulsion system able to convert the solar radiation pressure in a continuous thrust by means of a large, lightweight and highly reflective surface. Using the state-of-the-art level of solar sail technology, this paper studies the performance of a solar-sail-based transfer trajectory toward an ETa from an optimal viewpoint and with a parametric approach.

]]>Universe doi: 10.3390/universe9040185

Authors: J. Socorro J. Juan Rosales

Using a particular form of the quantum K-essence scalar field, we show that in the quantum formalism, a fractional differential equation in the scalar field variable, for some epochs in the Friedmann&ndash;Lema&#305;^tre&ndash;Robertson&ndash;Walker (FLRW) model (radiation and inflation-like epochs, for example), appears naturally. In the classical analysis, the kinetic energy of scalar fields can falsify the standard matter in the sense that we obtain the time behavior for the scale factor in all scenarios of our Universe by using the Hamiltonian formalism, where the results are analogous to those obtained by an algebraic procedure in the Einstein field equations with standard matter. In the case of the quantum Wheeler&ndash;DeWitt (WDW) equation for the scalar field &#981;, a fractional differential equation of order &beta;=2&alpha;2&alpha;&minus;1 is obtained. This fractional equation belongs to different intervals, depending on the value of the barotropic parameter; that is to say, when &omega;X&isin;[0,1], the order belongs to the interval 1&le;&beta;&le;2, and when &omega;X&isin;[&minus;1,0), the order belongs to the interval 0&lt;&beta;&le;1. The corresponding quantum solutions are also given.

]]>Universe doi: 10.3390/universe9040184

Authors: Sandor Nagy Kornel Sailer

Simple interpolation formulas are proposed for the description of the renormalization group (RG) scale dependences of the gravitational couplings in the framework of the 2-parameters Einstein-Hilbert (EH) theory of gravity and applied to a simple, analytically solvable, spatially homogeneous and isotropic, spatially flat model universe. The analytical solution is found in two schemes incorporating different methods of the determination of the conversion rule k(t) of the RG scale k to the cosmological time t. In the case of the discussed model these schemes turn out to yield identical cosmological evolution. Explicit analytical formulas are found for the conversion rule k(t) as well as for the characteristic time scales tG and t&Lambda;&gt;tG corresponding to the dynamical energy scales kG and k&Lambda;, respectively, arising form the RG analysis of the EH theory. It is shown that there exists a model-dependent time scale td (tG&le;td&lt;t&Lambda;) at which the accelerating expansion changes to the decelerating one. It is shown that the evolution runs from a well-identified cosmological fixed point to another one. As a by-product we show that the entropy of the system decreases monotonically in the interval 0&lt;t&le;t&Lambda; due to the quantum effects.

]]>Universe doi: 10.3390/universe9040183

Authors: Tsung-Han Yeh Keith A. Olive Brian D. Fields

We explore the effect of neutron lifetime and its uncertainty on standard big bang nucleosynthesis (BBN). BBN describes the cosmic production of the light nuclides, 1H, D, 3H+3He, 4He, and 7Li+7Be, in the first minutes of cosmic time. The neutron mean life &tau;n has two roles in modern BBN calculations: (1) it normalizes the matrix element for weak n&harr;p interconversions, and (2) it sets the rate of free neutron decay after the weak interactions freeze-out. We review the history of the interplay between &tau;n measurements and BBN, and present a study of the sensitivity of the light element abundances to the modern neutron lifetime measurements. We find that &tau;n uncertainties dominate the predicted 4He error budget, but these theory errors remain smaller than the uncertainties in 4He observations, even with the dispersion in recent neutron lifetime measurements. For the other light element predictions, &tau;n contributes negligibly to their error budget. Turning the problem around, we combine present BBN and cosmic microwave background (CMB) determinations of the cosmic baryon density to predict a &ldquo;cosmologically preferred&rdquo; mean life of &tau;n(BBN+CMB)=870&plusmn;16s, which is consistent with experimental mean life determinations. We show that if future astronomical and cosmological helium observations can reach an uncertainty of &sigma;obs(Yp)=0.001 in the 4He mass fraction Yp, this could begin to discriminate between the mean life determinations.

]]>Universe doi: 10.3390/universe9040182

Authors: Weizhi Xiong Chao Peng

A proton is a bound state of a strong interaction, governed by Quantum Chromodynamics (QCD). The electric charge radius of a proton, denoted by rEp, characterizes the spatial distribution of its electric charge carried by the quarks. It is an important input for bound-state Quantum Electrodynamic (QED) calculations of the hydrogen atomic energy levels. However, physicists have been puzzled by the large discrepancy between rEp measurements from muonic hydrogen spectroscopy and those from ep elastic scattering and ordinary hydrogen spectroscopy for over a decade. Tremendous efforts, both theoretical and experimental, have been dedicated to providing various insights into this puzzle, but certain issues still remain unresolved, particularly in the field of lepton scatterings. This review will focus on lepton-scattering measurements of rEp, recent theoretical and experimental developments in this field, as well as future experiments using this technique.

]]>Universe doi: 10.3390/universe9040181

Authors: Ana Rita Ribeiro Daniele Vernieri Francisco S. N. Lobo

General Relativity is an extremely successful theory, at least for weak gravitational fields; however, it breaks down at very high energies, such as in correspondence to the initial singularity. Quantum Gravity is expected to provide more physical insights in relation to this open question. Indeed, one alternative scenario to the Big Bang, that manages to completely avoid the singularity, is offered by Loop Quantum Cosmology (LQC), which predicts that the Universe undergoes a collapse to an expansion through a bounce. In this work, we use metric f(R) gravity to reproduce the modified Friedmann equations which have been obtained in the context of modified loop quantum cosmologies. To achieve this, we apply an order reduction method to the f(R) field equations, and obtain covariant effective actions that lead to a bounce, for specific models of modified LQC, considering a massless scalar field.

]]>Universe doi: 10.3390/universe9040180

Authors: Wanpeng Tan

This paper reviews the puzzles in modern neutron lifetime measurements and related unitarity issues in the CKM matrix. It is not a comprehensive and unbiased compilation of all historic data and studies, but rather a focus on compelling evidence leading to new physics. In particular, the largely overlooked nuances of different techniques applied in material and magnetic trap experiments are clarified. Further detailed analysis shows that the &ldquo;beam&rdquo; approach of neutron lifetime measurements is likely to give the &ldquo;true&rdquo; &beta;-decay lifetime, while discrepancies in &ldquo;bottle&rdquo; measurements indicate new physics at play. The most feasible solution to these puzzles is a newly proposed ordinary-mirror neutron (n&minus;n&prime;) oscillation model under the framework of mirror matter theory. This phenomenological model is reviewed and introduced, and its explanations of the neutron lifetime anomaly and possible non-unitarity of the CKM matrix are presented. Most importantly, various new experimental proposals, especially lifetime measurements with small/narrow magnetic traps or under super-strong magnetic fields, are discussed in order to test the surprisingly large anomalous signals that are uniquely predicted by this new n&minus;n&prime; oscillation model.

]]>Universe doi: 10.3390/universe9040179

Authors: Rositsa Miteva Mohamed Nedal Susan W. Samwel Manuela Temmer

In this study, we give correlations between the geomagnetic storm (GS) intensity and parameters of solar and interplanetary (IP) phenomena. We also perform 3D geometry reconstructions of geo-effective coronal mass ejections (CMEs) using the recently developed PyThea framework and compare on-sky and de-projected parameter values, focusing on the reliability of the de-projection capabilities. We utilize spheroid, ellipsoid and graduated cylindrical shell models. In addition, we collected a number of parameters of the GS-associated phenomena. A large variation in 3D de-projections is obtained for the CME speeds depending on the selected model for CME reconstruction and observer subjectivity. A combination of fast speed and frontal orientation of the magnetic structure upon its arrival at the terrestrial magnetosphere proves to be the best indicator for the GS strength. More reliable estimations of geometry and directivity, in addition to de-projected speeds, are important for GS forecasting in operational space weather schemes.

]]>Universe doi: 10.3390/universe9040178

Authors: Lei Wang Jin Min Yang Yang Zhang Pengxuan Zhu Rui Zhu

The Higgs boson may serve as a portal to new physics beyond the standard model (BSM), which is implied by the theoretical naturalness or experimental anomalies. This review aims to briefly survey some typical Higgs-related BSM models. First, for the theories to solve the hierarchy problem, the two exemplary theories, the low energy supersymmetry (focusing on the minimal supersymmetric model) and the little Higgs theory, are discussed. For the phenomenological models without addressing the hierarchy problem, we choose the two-Higgs-doublet models (2HDMs) to emphatically elucidate their phenomenological power in explaining current measurements of muon g&minus;2, the W-boson mass and the dark matter (DM) data. For the singlet extensions, which are motivated by the cosmic phase transition and the DM issue, we illustrate the singlet-extended standard model (xSM) and the singlet-extended 2HDM (2HDM+S), emphasizing the vacuum stability. In the decade since the discovery of the Higgs boson, these theories have remained the typical candidates of new physics, which will be intensively studied in future theoretical and experimental research.

]]>Universe doi: 10.3390/universe9040177

Authors: Hua-Hui Yan Jing-Kun Zhao Wei-Bin Shi Jin-Cheng Guo Liang Wang Zhen-Xin Lei Gang Zhao

We obtained spectroscopy data for 761 Degenerate A (DA)white dwarfs (WDs) with multiple LAMOST observations. The radial velocity (RV) of each spectrum was calculated using the cross-correlation function method (CCF), and 60 DA WD binary candidates were selected based on the variation of the RV. Then, the atmosphere parameter Teff, logg, and the mass of these DA WDs were estimated by the Balmer line fitting method and interpolation in theoretical evolution tracks, respectively. Our parameters are consistent with those from SDSS and Gaia for the common stars. No evident difference in the mass distribution of binary candidates compared with total DA WDs was found. We surmise these DA WD binary candidates are mainly composed of two WDs. With the Zwicky Transient Facility (ZTF) data, we obtained the light curve periods of two targets with significant light curve periods in the DA WD binary candidates. For the spectra with anomalous CCF curves or with large errors in their RV calculations, we re-certified their spectral types by visual review. Based on their spectral features, we found 11 DA + M-type binaries and four cataclysmic variables (CVs). The light curve period of one CV was obtained with ZTF data.

]]>Universe doi: 10.3390/universe9040176

Authors: Kristina Giesel Hongguang Liu

We consider an extended phase space formulation for cosmological and spherically symmetric models in which the choice of a given &mu;&macr;-scheme can be implemented dynamically. These models are constructed in the context of the relational formalism by using a canonical transformation on the extended phase space, which provides a Kucha&#345; decomposition of the extended phase space. The resulting model can be understood as a gauge-unfixed model of a given &mu;&macr;-scheme. We use this formalism to investigate the restrictions to the allowed &mu;&macr;-scheme from this perspective and discuss the differences in the cosmological and spherically symmetric case. This method can be useful, for example, to obtain a &mu;&macr;-scheme in a top-down derivation from full LQG to symmetry-reduced effective models, where, for some models, only the &mu;0-scheme has been obtained thus far.

]]>Universe doi: 10.3390/universe9040175

Authors: Mikhail Piotrovich Stanislava Buliga Tinatin Natsvlishvili

We estimated the spin values of the supermassive black holes (SMBHs) of the active galactic nuclei (AGN) for a large set of Narrow Line Seyfert 1 (NLS1) galaxies assuming the inclination angle between the line of sight and the axis of the accretion disk to be approximately 45 degrees. We found that for these objects the spin values are on average less than for the Seyfert 1 galaxies that we studied previously. In addition, we found that the dependencies of the spin on the bolometric luminosity and the SMBH mass are two to three times stronger that for Seyfert 1 galaxies, which could mean that at early stages of evolution NLS1 galaxies either have a low accretion rate or chaotic accretion, while at later stages they have standard disk accretion, which very effectively increases the spin value.

]]>Universe doi: 10.3390/universe9040174

Authors: Krista L. Smith

Heavy-ion research at the Relativistic Heavy Ion Collider (RHIC) during the first decade of data collection, approximately during the years 2000&ndash;2010, was primarily focused on the study of Au+Au collisions. The search for evidence of quark-gluon plasma (QGP), a state of matter where quarks and gluons become unbound within a high energy density environment, which was at the forefront of research efforts. However, studies of the azimuthal anisotropy parameter v2 in p/d+Pb collisions from the Large Hadron Collider (LHC) yielded results consistent with the hydrodynamic flow, one of the signatures of quark-gluon plasma formation in heavy-ion collisions. Since the publication of these findings, the field of heavy-ion physics has made subsequent measurements in small system collisions to study cold nuclear matter effects as well as look for additional evidence of hot nuclear matter effects. Quarkonia, a bound state of a cc&macr; or bb&macr; pair, has often been used to probe a wide range of nuclear effects in both large and small collision systems. Here we will review recent quarkonia measurements in small system collisions at RHIC and LHC energies and summarize the experimental conclusions.

]]>Universe doi: 10.3390/universe9040173

Authors: Albert Schwarz

Using the geometric approach, we formulate a quantum theory in terms of Jordan algebras. We analyze the notion of a (quasi)particle (=elementary excitation of translation-invariant stationary state) and the scattering of (quasi)particles in this framework.

]]>Universe doi: 10.3390/universe9040172

Authors: Rodger I. Thompson

The primary purpose of this work is the provision of accurate, analytic, evolutionary templates for cosmological parameters and fundamental constants in a dynamical cosmology. A flat quintessence cosmology with a dark energy potential that has the mathematical form of the Higgs potential is the specific cosmology and potential addressed in this work. These templates, based on the physics of the cosmology and potential, are intended to replace those parameterizations currently used to determine the likelihoods of dynamical cosmologies. Acknowledging that, unlike &Lambda;CDM, the evolutions are dependent on both the specific cosmology and the dark energy potential, the templates are referred to as specific cosmology and potential (SCP) templates. The requirements set for the SCP templates are that they must be accurate, analytic functions of an observable, such as the scale factor or redshift. This is achieved through the utilization of a modified beta function formalism that is based on a physically motivated dark energy potential to calculate the beta function. The methodology developed here is designed to be adaptable to other cosmologies and dark energy potentials. The SCP templates are essential tools in determining the relative likelihoods of a range of dynamical cosmologies and potentials. The ultimate purpose is the determination of whether dark energy is dynamical or static in a quantitative manner. It is suggested that the SCP templates calculated in this work can serve as fiducial dynamical templates in the same manner as &Lambda;CDM serves for static dark energy.

]]>Universe doi: 10.3390/universe9040171

Authors: Wolfgang Lucha

Motivated by recent experimental progress in establishing the likely existence of (variants of) exotic hadrons, predicted to be formed by the strong interactions, various proposed concepts and ideas are compiled in an attempt to draft a coherent picture of the achievable improvement in the theoretical interpretation of exotic hadrons in terms of the underlying quantum field theory of strong interactions.

]]>Universe doi: 10.3390/universe9040170

Authors: Shubhangi Jain Rohit Gupta Satyajit Jena

The thermodynamical quantities and response functions are useful to describe the particle production in heavy-ion collisions as they reveal crucial information about the produced system. While the study of isothermal compressibility provides an inference about the viscosity of the medium, speed of sound helps in understanding the equation of state. With an aim towards understanding the system produced in the heavy-ion collision, we have made an attempt to study isothermal compressibility and speed of sound as function of charged particle multiplicity in heavy-ion collisions at sNN = 2.76 TeV, 5.02 TeV, and 5.44 TeV using unified formalism.

]]>Universe doi: 10.3390/universe9040169

Authors: Giulia Maniccia Giovanni Montani Leonardo Torcellini

After a brief review of the different approaches to predicting the possible quantum gravity corrections to quantum field theory, we discuss in some detail the formulation based on a Gaussian reference frame fixing. Then, we utilize this scenario in the determination of the inflationary spectrum of primordial perturbations. We consider the quantization of an inhomogeneous, free, massless scalar field in a quasi-classical isotropic Universe by developing a WKB expansion of the dynamics of the next order in the Planckian parameter, with respect to the one at which standard QFT emerges. The quantum gravity corrections to the scale-invariant spectrum are discussed in a specific primordial cosmological setting and then in a general minisuperspace formalism, showing that there is no mode-dependent effect, and thus the scale invariant inflationary spectrum is preserved. This result is discussed in connection to the absence of a matter backreaction on the gravitational background in the considered paradigm.

]]>Universe doi: 10.3390/universe9040168

Authors: Arjun Berera Jaime Calderón-Figueroa

This paper reviews the theoretical and phenomenological implications of the swampland conjectures from the perspective of inflationary cosmology, focusing on warm inflation. We demonstrate how the swampland conjectures appear to favor the strong dissipative regime, giving warm inflation a competitive edge over standard inflation. Additionally, we ponder the possible deeper implications of dissipation for constructing successful inflation models from string theory.

]]>Universe doi: 10.3390/universe9040167

Authors: Héctor J. de Vega Norma G. Sanchez

We uncover the general mechanism and the nature of today&rsquo;s dark energy (DE). This is only based on well-known quantum physics and cosmology. We show that the observed DE today originates from the cosmological quantum vacuum of light particles, which provides a continuous energy distribution able to reproduce the data. Bosons give positive contributions to the DE, while fermions yield negative contributions. As usual in field theory, ultraviolet divergences are subtracted from the physical quantities. The subtractions respect the symmetries of the theory, and we normalize the physical quantities to be zero for the Minkowski vacuum. The resulting finite contributions to the energy density and the pressure from the quantum vacuum grow as loga(t), where a(t) is the scale factor, while the particle contributions dilute as 1/a3(t), as it must be for massive particles. We find the explicit dark energy equation of state of today to be P=w(z)H: it turns to be slightly w(z)&lt;&minus;1 with w(z) asymptotically reaching the value &minus;1 from below. A scalar particle can produce the observed dark energy through its quantum cosmological vacuum provided that (i) its mass is of the order of 10&minus;3 eV = 1 meV, (ii) it is very weakly coupled, and (iii) it is stable on the time scale of the age of the universe. The axion vacuum thus appears as a natural candidate. The neutrino vacuum (especially the lightest mass eigenstate) can give negative contributions to the dark energy. We find that w(z=0) is slightly below &minus;1 by an amount ranging from (&minus;1.5&times;10&minus;3) to (&minus;8&times;10&minus;3) and we predict the axion mass to be in the range between 4 and 5 meV. We find that the universe will expand in the future faster than the de Sitter universe as an exponential in the square of the cosmic time. Dark energy today arises from the quantum vacuum of light particles in FRW cosmological space-time in an analogous way to the Casimir vacuum effect of quantum fields in Minkowski space-time with non-trivial boundary conditions.

]]>Universe doi: 10.3390/universe9040166

Authors: Christian Böhmer Erik Jensko Ruth Lazkoz

Modified gravity theories can be used for the description of homogeneous and isotropic cosmological models through the corresponding field equations. These can be cast into systems of autonomous differential equations because of their sole dependence on a well-chosen time variable, be it the cosmological time, or an alternative. For that reason, a dynamical systems approach offers a reliable route to study those equations. Through a model-independent set of variables, we are able to study all f(Q) modified gravity models. The drawback of the procedure is a more complicated constraint equation. However, it allows the dynamical system to be formulated in fewer dimensions than using other approaches. We focus on a recent model of interest, the power-exponential model, and generalize the fluid content of the model.

]]>Universe doi: 10.3390/universe9040165

Authors: Komal Hassan Muhammad Sharif

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.

]]>Universe doi: 10.3390/universe9040164

Authors: Yao Yu Ze-Jun Hu Hong-Tao Cai Yi-Sheng Zhang

Two important phenomena of the solar wind&ndash;magnetosphere&ndash;ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600&ndash;1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70&ndash;80&deg;.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn&ndash;dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500&ndash;1800 MLT and 0600&ndash;0900 MLT, with the MLAT range below 70&deg;. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75&deg; increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer.

]]>Universe doi: 10.3390/universe9040163

Authors: Lakhan V. Jaybhaye Raja Solanki Sanjay Mandal Pradyumn Kumar Sahoo

In this article, we attempt to describe the cosmic late-time acceleration of the universe in the framework of f(R,Lm) gravity, by using an effective equation of state, when bulk viscosity is taken into account. We presume a non-linear f(R,Lm) functional form, specifically, f(R,Lm)=R2+Lm&alpha;, where &alpha; is a free model parameter. We obtain the exact solution of our bulk viscous matter dominated f(R,Lm) model, and then we utilize the combined H(z) + Pantheon + Analysis datasets to estimate the best fit values of the free parameters of our model. Then, we characterize the behavior of the matter&ndash;energy density, effective pressure, and the equation of state (EoS) parameter, incorporating the viscous type fluid. The evolution profile of the effective EoS parameter depicts an acceleration phase of the cosmic expansion, whereas the pressure, with the effect of viscosity, exhibits negative behavior, that can lead to the accelerating expansion of the universe. Moreover, the cosmic matter&ndash;energy density shows the expected positive behavior. Further, we investigate the behavior of the statefinder parameters for the assumed f(R,Lm) model. We find that the evolutionary trajectory of the given model lies in the quintessence region. In addition, we employ the Om diagnostic test, that indicates that our model exhibits quintessence behavior. Lastly, we check the energy condition criteria and find that the violation of SEC occurs in the past, whereas NEC and DEC satisfy the positivity criteria. We find that our f(R,Lm) cosmological model, with the effect of bulk viscosity, provides a good fit of the recent observational data and can efficiently describe the cosmic expansion scenario.

]]>Universe doi: 10.3390/universe9040162

Authors: Edward A. Rietman Brandon Melcher Alexey Bobrick Gianni Martire

We describe the construction of an optical-space, cylindrical black hole induced by high pressure in a dense fluid. Using an approximate analogy between curved spacetime and optics in moving dielectric media, we derive the mass of the black hole thus created. We describe the resulting optical-space using a Bessel beam profile and Snell&rsquo;s law to understand how total internal reflection produces a cylindrical, optic black hole.

]]>Universe doi: 10.3390/universe9040161

Authors: Ambuj Kumar Mishra Shweta Umesh Kumar Sharma

Casimir energy is always suggested as a possible source to create a traversable wormhole. It is also used to demonstrate the existence of negative energy, which can be created in a lab. To generalize this idea, Yukawa modification of a Casimir source has been considered in Remo Garattini (Eur. Phys. J. C 81 no.9, 824, 2021). In this work, we explore the Yukawa&ndash;Casimir wormholes in symmetric teleparallel gravity. We have taken four different forms of f(Q) to obtain wormhole solutions powered by the original Casimir energy source and Yukawa modification of the Casimir energy source. In power law form f(Q)=&alpha;Q2+&beta; and quadratic form f(Q)=&alpha;Q2+&beta;Q+&gamma;, where &alpha;,&beta;,&gamma; are constants and Q is non-metricity scalar, we analyze that wormhole throat is filled with non-exotic matter. We find self-sustained traversable wormholes in the Casimir source where null energy conditions are violated in all specific forms of f(Q), while after Yukawa modification, it is observed that violation of null energy conditions is restricted to some regions in the vicinity of the throat.

]]>Universe doi: 10.3390/universe9040160

Authors: Ewa Czuchry

The standard &Lambda;CDM model, despite its agreement with observational data, still has some issues unaddressed, such as the problem of initial singularity. Solving that problem usually requires modifications of general relativity. However, there appeared the Ho&#345;ava&ndash;Lifshitz (HL) theory of gravity, in which equations governing cosmological evolution include a new term scaling similarly as the dark radiation term in the Friedmann equations, enabling a bounce of the universe instead of initial singularity. This review describes past works on the stability of such a bounce in different formulations of HL theory, an initial detailed balance scenario, and further projectable versions containing higher than quadratic terms to the original action.

]]>Universe doi: 10.3390/universe9040159

Authors: Marija Tomašević

We will explain why time machines, although allowed in General Relativity, cannot be accessed by observers once we include quantum effects. Moreover, we will show that traversable wormholes cannot be turned into time machines without invoking the effects of quantum gravity.

]]>Universe doi: 10.3390/universe9040158

Authors: Paloma Rodriguez Casale Jose E. Amaro Victor L. Martinez-Consentino Ignacio Ruiz Simo

Superscaling in electron scattering from nuclei is re-examined, paying special attention to the definition of the averaged single-nucleon responses. The validity of the extrapolation of nucleon responses in the Fermi gas has been examined, which previously lacked a theoretical foundation. To address this issue, we introduce new averaged responses with a momentum distribution smeared around the Fermi surface, allowing for momenta above the Fermi momentum. This approach solves the problem of negativity in the extrapolation away from the scaling region and, at the same time, validates its use in the scaling analysis. This work has important implications for the interpretation of scaling data and contributes to the development of a more complete understanding of the scaling approach.

]]>Universe doi: 10.3390/universe9040157

Authors: Zhi-Chao Zhao Sai Wang

Assuming that the common-spectrum process in the NANOGrav 12.5-year dataset has an origin of scalar-induced gravitational waves, we study the enhancement of primordial curvature perturbations and the mass function of primordial black holes, by performing the Bayesian parameter inference for the first time. We obtain lower limits on the spectral amplitude, i.e., A&#8819;10&minus;2 at 95% confidence level, when assuming the power spectrum of primordial curvature perturbations to follow a log-normal distribution function with width &sigma;. In the case of &sigma;&rarr;0, we find that the primordial black holes with 2&times;10&minus;4&minus;10&minus;2 solar mass are allowed to compose at least a fraction 10&minus;6 of dark matter. Such a mass range is shifted to more massive regimes for larger values of &sigma;, e.g., to a regime of 4&times;10&minus;3&minus;0.2 solar mass in the case of &sigma;=1. We expect the planned gravitational-wave experiments to have their best sensitivity to A in the range of 10&minus;4 to 10&minus;7, depending on the experimental setups. With this level of sensitivity, we can search for primordial black holes throughout the entire parameter space, especially in the mass range of 10&minus;16 to 10&minus;11 solar masses, where they could account for all dark matter. In addition, the importance of multi-band detector networks is emphasized to accomplish our theoretical expectation.

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