Universe doi: 10.3390/universe8120648

Authors: Zbigniew Haba

A stochastic metric can appear in classical as well as in quantum gravity. We show that if the linearized stochastic Gaussian gravitational-plane wave has the frequency spectrum &omega;4&gamma;&minus;1 (0&le;&gamma;&lt;1), then the equal-time propagator of the scalar field behaves as p&minus;11&minus;&gamma; for large momenta. We discuss models of quantum-field theory where such anomalous behavior can appear.

]]>Universe doi: 10.3390/universe8120647

Authors: Surajit Kalita Lupamudra Sarmah Aneta Wojnar

A simple cooling model of white dwarf stars is re-analyzed in Palatini f(R) gravity. Modified gravity affects the white dwarf structures and consequently their ages. We find that the resulting super-Chandrasekhar white dwarfs need more time to cool down than sub-Chandrasekhar ones, or when compared to the Newtonian models.

]]>Universe doi: 10.3390/universe8120646

Authors: Ivan Berezin Andrey Tlatov

The Wang&ndash;Sheeley&ndash;Arge (WSA) solar wind (SW) model is based on the idea that weakly expanding coronal magnetic field tubes are associated with sources of fast SWs and vice versa. A parameter called the &ldquo;flux tube expansion&rdquo; (FTE) is used to determine the degree of expansion of magnetic tubes. The FTE is calculated based on the coronal magnetic field model, usually in the potential approximation. The second input parameter for the WSA model is the great circle distance from the base of the open magnetic field line in the photosphere to the boundary of the corresponding coronal hole (DCHB). These two coronal magnetic field parameters are related by an empirical relationship with the solar wind velocity near the Sun. The WSA model has shortcomings and does not fully explain the solar wind formation mechanisms. In the present work, we model various coronal magnetic field parameters in the potential-field source-surface (PFSS) approximation from a long series of magnetographic observations: the Solar Telescope-magnetograph for Operative Prognoses (STOP) (Kislovodsk Mountain Astronomical Station), the Helioseismic and magnetic imager (SDO/HMI), and data from the Wilcox Solar Observatory (WSO). Our main goal is to identify correlations between the coronal magnetic field parameters and the observed SW velocity in order to use them for modeling SW. We found that the SW velocity correlates relatively well with some geometric properties of the magnetic tubes, including the force line length, the latitude of the force line footpoints, and the DCHB. We propose a formula for calculating the SW velocity based on these parameters. The presented relationship does not use FTE and showed a better correlation with observations compared to the WSA model.

]]>Universe doi: 10.3390/universe8120645

Authors: Fabio Scardigli

A universal upper limit on the entropy contained in a localized quantum system of a given size and total energy is expressed by the so-called Bekenstein bound. In a previous paper [Buoninfante, L. et al. 2022], on the basis of general thermodynamic arguments, and in regimes where the equipartition theorem still holds, the Bekenstein bound has been proved practically equivalent to the Heisenberg uncertainty relation. The smooth transition between the Bekenstein bound and the holographic bound suggests a new pair of canonical non-commutative variables, which could be thought to hold in strong gravity regimes.

]]>Universe doi: 10.3390/universe8120644

Authors: Alan P. Marscher Svetlana G. Jorstad

Blazars whose synchrotron spectral energy distribution (SED) peaks at X-ray energies need to accelerate electrons to energies in the &gt;100 GeV range in relativistic plasma jets at distances of parsecs from the central engine. Compton scattering by the same electrons can explain high luminosities at very high photon energies (&gt;100 GeV) from the same objects. Turbulence combined with a standing conical shock can accomplish this. Such a scenario can also qualitatively explain the level and variability of linear polarization observed at optical frequencies in these objects. Multi-wavelength polarization measurements, including those at X-ray energies by the Imaging X-ray Polarimetry Explorer (IXPE), find that the degree of polarization is several times higher at X-ray than at optical wavelengths, in general agreement with the turbulence-plus-shock picture. Some detailed properties of the observed polarization can be naturally explained by this scenario, while others pose challenges that may require modifications to the model.

]]>Universe doi: 10.3390/universe8120643

Authors: Kim L. Page N. Paul M. Kuin Julian P. Osborne

With rapid response capabilities, and a daily planning of its observing schedule, the Neil Gehrels Swift Observatory is ideal for monitoring transient and variable sources. Here we present a sample of the 12 novae with the most detailed ultraviolet (UV) follow-up by Swift&mdash;the first uniform analysis of such UV light-curves. The fading of these specific light-curves can be modelled as power-law decays (plotting magnitude against log time), showing that the same physical processes dominate the UV emission for extended time intervals in individual objects. After the end of the nuclear burning interval, the X-ray emission drops significantly, fading by a factor of around 10&ndash;100. The UV changes, however, are of a lower amplitude, declining by 1&ndash;2 mag over the same time period. The UV light-curves typically show a break from flatter to steeper around the time at which the X-ray light-curve starts a steady decline from maximum, &sim;0.7&ndash;1.3 TSSSend. Considering populations of both classical and recurrent novae, and those with main sequence or giant companions, we do not find any strong differences in the UV light-curves or their evolution, although the long-period recurrent novae are more luminous than the majority of the classical novae.

]]>Universe doi: 10.3390/universe8120642

Authors: Umesh Sharma Mukesh Kumar Gunjan Varshney

This research study investigates Barrow holographic dark energy with an energy density of ρΛ=CH2−Δ by considering the Hubble horizon as the IR cut-off in the f(R, T) gravity framework. We employ Barrow holographic dark energy to obtain the equation of the state for the Barrow holographic energy density in a flat FLRW Universe. Concretely, we study the correspondence between quintessence, k-essence, and dilation scalar field models with the Barrow holographic dark energy in a flat f(R, T) Universe. Furthermore, we reconstruct the dynamics and potential for all these models for different values of the Barrow parameter: Δ. Via this study, we can show that for Barrow holographic quintessence, k-essence, and dilation scalar field models, if the corresponding model parameters satisfy some limitations, the accelerated expansion can be achieved.

]]>Universe doi: 10.3390/universe8120641

Authors: Shiqi Zhou Erbil Gügercinoğlu Jianping Yuan Mingyu Ge Cong Yu

&sim;6% of all known pulsars have been observed to exhibit sudden spin-up events, known as glitches. For more than fifty years, these phenomena have played an important role in helping to understand pulsar (astro)physics. Based on the review of pulsar glitches search method, the progress made in observations in recent years is summarized, including the achievements obtained by Chinese telescopes. Glitching pulsars demonstrate great diversity of behaviours, which can be broadly classified into four categories: normal glitches, slow glitches, glitches with delayed spin-ups, and anti-glitches. The main models of glitches that have been proposed are reviewed and their implications for neutron star structure are critically examined regarding our current understanding. Furthermore, the correlations between glitches and emission changes, which suggest that magnetospheric state-change is linked to the pulsar-intrinsic processes, are also described and discussed in some detail.

]]>Universe doi: 10.3390/universe8120640

Authors: Serguei Krasnikov

As follows from Gott&rsquo;s discovery, a pair of straight string-like singularities moving in opposite directions, when they have suitable speed and impact parameter, produce closed timelike curves. I argue in this paper that there always is a not-so-frightening alternative: the Universe may prefer to produce a certain (surprisingly simple and absolutely mild) singularity instead.

]]>Universe doi: 10.3390/universe8120639

Authors: Grigory E. Volovik

The double Hawking temperature T=2TH appears in some approaches to the Hawking radiation when the radiation is considered in terms of the quantum tunneling. We consider the origin of such unusual temperature for the black hole horizon and also for the cosmological horizon in de Sitter spacetime. In the case of the black hole horizon, there are two contributions to the tunneling process of radiation, each being governed by the temperature T=2TH. These processes are coherently combined to produce the radiation with the Hawking temperature TH. This can be traditionally interpreted as the pair creation of two entangled particles, of which one goes towards the center of the black hole, while the other one escapes from the black hole. In the case of the cosmological horizon, the temperature T=2TH is physical. While the creation of the entangled pair is described by the Hawking temperature, the de Sitter spacetime allows for another process, in which only a single (non-entangled) particle inside the cosmological horizon is created. This process is characterized by the local temperature T=2TH. The local single-particle process also takes place outside the black hole horizon, but it is exponentially suppressed.

]]>Universe doi: 10.3390/universe8120638

Authors: Freya Blekman Fréderic Déliot Valentina Dutta Emanuele Usai

The production of four top quarks presents a rare process in the Standard Model that provides unique opportunities and sensitivity to Standard Model observables including potential enhancement of many popular new physics extensions. This article summarises the latest experimental measurements of the four-top quark production cross section at the LHC. An overview is provided detailing interpretations of the experimental results regarding the top quark Yukawa coupling in addition to the limits on physics beyond the Standard Model. Further, prospects for future measurements and opportunities offered by this challenging final state are given herein.

]]>Universe doi: 10.3390/universe8120637

Authors: Anastasia Tezari Argyris N. Stassinakis Pavlos Paschalis Helen Mavromichalaki Christina Plainaki Anastasios Kanellakopoulos Norma Crosby Mark Dierckxsens Pantelis Karaiskos

The new space era has expanded the exploration of other planets of our solar system. In this work, radiation quantities are estimated in the Venusian atmosphere using the software tool DYASTIMA/DYASTIMA-R, such as the energy deposit and the ambient dose equivalent rate. Monte Carlo simulations of the secondary particle cascades for different atmospheric layers were performed during solar minimum and solar maximum conditions, as well as during the extreme solar particle event that took place in October 1989, with a focus on the so-called Venusian zone of habitability.

]]>Universe doi: 10.3390/universe8120636

Authors: Santosh V. Lohakare Francisco Tello-Ortiz S. K. Tripathy B. Mishra

In this paper, we studied the bouncing behavior of the cosmological models formulated in the background of the Hubble function in the F(R,G) theory of gravity, where R and G, respectively, denote the Ricci scalar and Gauss&ndash;Bonnet invariant. The actions of the bouncing cosmology are studied with a consideration of the different viable models that can resolve the difficulty of singularity in standard Big Bang cosmology. Both models show bouncing behavior and satisfy the bouncing cosmological properties. Models based on dynamical, deceleration, and energy conditions indicate the accelerating behavior at the late evolution time. The phantom at the bounce epoch is analogous to quintessence behavior. Finally, we formulate the perturbed evolution equations and investigate the stability of the two bouncing solutions.

]]>Universe doi: 10.3390/universe8120635

Authors: Stanislav Kuptsov Mikhail Ioffe Sergey Manida Sergey Paston

We study a perturbation theory for embedding gravity equations in a background for which corrections to the embedding function are linear with respect to corrections to the flat metric. The remaining arbitrariness after solving the linearized field equations is fixed by an assumption that the solution is static in the second order. A nonlinear differential equation is obtained, which allows for finding the gravitational potential for a spherically symmetric case if a background embedding is given. An explicit form of a spherically symmetric background parameterized by one function of radius is proposed. It is shown that this function can be chosen in such a way that the gravitational potential is in a good agreement with the observed distribution of dark matter in a galactic halo.

]]>Universe doi: 10.3390/universe8120634

Authors: Basabendu Barman Nicolás Bernal Nicklas Ramberg Luca Visinelli

The axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the Peccei&ndash;Quinn (PQ) symmetry, could have originated with initial non-zero velocity. The presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the PQ symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional PQ framework or an explanation for the observed matter-antimatter asymmetry. We elaborate further on the consequences of the &ldquo;kinetic misalignment&rdquo; mechanism, assuming that axions form the entirety of the dark matter abundance. The kinetic misalignment mechanism possesses a weak limit in which the axion field starts to oscillate at the same temperature as in the conventional PQ framework, and a strong limit corresponding to large initial velocities which effectively delay the onset of oscillations. Following a UV-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures.

]]>Universe doi: 10.3390/universe8120633

Authors: Guang-Lei Wu Yun-Wei Yu Shao-Ze Li

A rapidly rotating and highly magnetized remnant neutron star (NS; magnetar) could survive from a merger of double NSs and drive a powerful relativistic wind. The early interaction of this wind with the previous merger ejecta can lead to shock breakout (SBO) emission mainly in ultraviolet and soft X-ray bands, which provides an observational signature for the existence of the remnant magnetar. Here, we investigate the effect of an anisotropic structure of the merger ejecta on the SBO emission. It is found that the bolometric light curve of the SBO emission can be broadened, since the SBO can occur at different times for different directions. In more detail, the profile of the SBO light curve can be highly dependent on the ejecta structure and, thus, we can in principle use the SBO light curves to probe the structure of the merger ejecta in future.

]]>Universe doi: 10.3390/universe8120632

Authors: Sergey A. Larin

We suggest a new explanation of the flatness of galaxies rotation curves without invoking dark matter. For this purpose, a new gravitational tensor field is introduced in addition to the metric tensor.

]]>Universe doi: 10.3390/universe8120631

Authors: Denitsa Staicova

It has been theorized that dynamical dark energy (DDE) could be a possible solution to Hubble tension. To avoid degeneracy between Hubble parameter H0 and sound horizon scale rd, in this article, we use their multiplication as one parameter c/H0rd, and we use it to infer cosmological parameters for 6 models&mdash;&Lambda;CDM and 5 DDE parametrizations&mdash;the Chevallier&ndash;Polarski&ndash;Linder (CPL), the Barboza&ndash;Alcaniz (BA), the low correlation (LC), the Jassal&ndash;Bagla&ndash;Padmanabhan (JBP) and the Feng&ndash;Shen&ndash;Li-Li models. We choose a dataset that treats this combination as one parameter, which includes the baryon acoustic oscillation (BAO) data 0.11&le;z&le;2.40 and additional points from the cosmic microwave background (CMB) peaks (z&#8771;1090). To them, we add the marginalized Pantheon dataset and GRB dataset. We see that the tension is moved from H0 and rd to c/H0rd and &Omega;m. There is only one model that satisfies the Planck 2018 constraints on both parameters, and this is LC with a huge error. The rest cannot fit into both constraints. &Lambda;CDM is preferred, with respect to the statistical measures.

]]>Universe doi: 10.3390/universe8120630

Authors: Hamna Asad Zeeshan Yousaf

The core of this manuscript is to conduct a broad investigation into the features of static matter configurations with hyperbolical symmetry, which might possibly serve as formation of corresponding spacetime within the limits of f(R,T,Q) gravity, where (Q &equiv; R&alpha;&sigma;T&alpha;&sigma;). We recognize that such matter distributions can be anisotropic in pressure, with just two primary stresses unequal and a negative energy density. Usually, negative matter densities are suggested in extreme cosmological and astrophysical situations, particularly with regard to quantum occurrences that might occur within the horizon. Eventually, we construct a generic formalism that allows every static hyperbolically symmetric (HS) fluid solution to be expressed with respect to two generating functions (GFs).

]]>Universe doi: 10.3390/universe8120629

Authors: Waheed Akram Oliver Hallmann Bernd Pfeiffer Karl-Ludwig Kratz

In this paper we present an extension of our nucleosynthesis parameter study within the classical neutrino-driven wind scenario of core-collapse supernovae (ccSNe). The principal aim of this decade-old study was to shine light on the production of the historical &lsquo;p-only&rsquo; isotopes of the light trans-Fe elements in the Solar System (S.S.). One of our earliest key findings was the co-production of neighbouring classical &lsquo;s-only&rsquo; and &lsquo;r-only&rsquo; isotopes between Zn (Z = 30) and Ru (Z = 44), alongside the synthesis of light p-isotopes, under similar conditions of a moderately neutron-rich, low-entropy, charged-particle component of Type II SNe wind ejecta. We begin this analysis by expressing the need for nuclear-structure input from detailed spectroscopic experiments and microscopic models in the relevant shape-transition mass region between N = 50 and N = 60. Then, we focus on the unique nucleosynthetic origin of the anomalous isotopic compositions of Zr (Z = 40), Mo (Z = 42) and Ru (Z = 44) in presolar silicon carbide X-grains. In contrast to the interpretation of other studies, we show that these grains do not reflect the signature of a &lsquo;clean&rsquo; stellar scenario but are mixtures of an exotic rapid (r-process like) nucleosynthesis component and different fractions of S.S. material. Thus, the synthesis of these light isotopes through a &lsquo;primary&rsquo; production mode provides further means to revise the abundance estimates of the light trans-Fe elements in the S.S., reducing our dependence on still favoured &lsquo;secondary&rsquo; scenarios like Type Ia SNe or neutron-bursts in exploding massive stars.

]]>Universe doi: 10.3390/universe8120628

Authors: Cheng-Min Zhang Xiang-Han Cui Di Li De-Hua Wang Shuang-Qiang Wang Na Wang Jian-Wei Zhang Bo Peng Wei-Wei Zhu Yi-Yan Yang Yuan-Yue Pan

The evolutions of a neutron star&rsquo;s rotation and magnetic field (B-field) have remained unsolved puzzles for over half a century. We ascribe the rotational braking torques of pulsar to both components, the standard magnetic dipole radiation (MDR) and particle wind flow (MDR + Wind, hereafter named MDRW), which we apply to the Crab pulsar (B0531 + 21), the only source with a known age and long-term continuous monitoring by radio telescope. Based on the above presumed simple spin-down torques, we obtain the exact analytic solution on the rotation evolution of the Crab pulsar, together with the related outcomes as described below: (1) unlike the constant characteristic B-field suggested by the MDR model, this value for the Crab pulsar increases by a hundred times in 50 kyr while its real B-field has no change; (2) the rotational braking index evolves from &sim;3 to 1 in the long-term, however, it drops from 2.51 to 2.50 in &sim;45 years at the present stage, while the particle flow contributes approximately 25% of the total rotational energy loss rate; (3) strikingly, the characteristic age has the maximum limit of &sim;10 kyr, meaning that it is not always a good indicator of a real age. Furthermore, we discussed the evolutionary path of the Crab pulsar from the MDR to the wind domination by comparing with the possible wind braking candidate pulsar PSR J1734-3333.

]]>Universe doi: 10.3390/universe8120627

Authors: Sergey Afonin

Recently, the CDF Collaboration has announced a new precise measurement of the W-boson mass MW that deviates from the Standard Model (SM) prediction by 7&sigma;. The discrepancy in MW is about &Delta;W &#8771; 70 MeV and is probably caused by a beyond the SM physics. Within a certain scenario of extension of the SM, we obtain the relation &Delta;W &#8771; 3&alpha;8&pi;MW &#8771; 70 MeV, where &alpha; is the electromagnetic fine structure constant. The main conjecture is the appearance of longitudinal components of the W-bosons as the Goldstone bosons of a spontaneously broken additional SU(2) global symmetry at distances much smaller than the electroweak symmetry breaking scale rEWSB. We argue that within this scenario, the masses of charged Higgs scalars can obtain an electromagnetic radiative contribution which enhances the observed value of MW&plusmn; with respect to the usual SM prediction. Our relation for &Delta;W follows from the known one-loop result for the corresponding effective Coleman&ndash;Weinberg potential in combination with the Weinberg sum rules.

]]>Universe doi: 10.3390/universe8120626

Authors: Sergey Cherkas Vladimir Kalashnikov

The fact that quantum gravity does not admit an invariant vacuum state has far-reaching consequences for all physics. It points out that space could not be empty, and we return to the notion of an &aelig;ther. Such a concept requires a preferred reference frame for describing universe expansion and black holes. Here, we intend to find a reference system or class of metrics that could be attributed to &ldquo;&aelig;ther&rdquo;. We discuss a vacuum and quantum gravity from three essential viewpoints: universe expansion, black hole existence, and quantum decoherence.

]]>Universe doi: 10.3390/universe8120625

Authors: Job Furtado Geová Alencar

In this paper, we study the charged and uncharged BTZ counterpart of the black-bounce proposed by Simpson and Visser recently. For the uncharged case, we find that the temperature is not modified by the bounce parameter. We also find that the wormhole side of the solution must always be supported by exotic matter over the throat. For the charged case, we find that the thermodynamics is changed and the bounce parameter controls a phase transition, affecting the sign of the heat capacity and therefore the stability of the system. For the uncharged case, we find that there are no stable orbits for both massive and massless incoming particles, while stable orbits are present for the charged case and the bounce parameter affects the points of stability.

]]>Universe doi: 10.3390/universe8120624

Authors: Pablo Marcos-Arenal Luis Cerdán Mercedes Burillo-Villalobos Nuria Fonseca-Bonilla Juan García de la Concepción María Ángeles López-Cayuela Felipe Gómez José A. Caballero

Only a low percentage of the radiation from our Sun is captured by photosynthesis, but this conversion of solar to chemical energy sustains all life on Earth. Photosynthesis could be present in any exoplanetary system fulfilling the main three ingredients for this metabolic route: light, water, and carbon dioxide. To deepen into this idea, the ExoPhot project aims to study the relation between photosynthetic systems and exoplanet conditions around different types of stars by focusing on two aspects: (i) Assessing the photosynthetic fitness of a variety of photopigments (either found on Earth or theoretical) as a function of stellar spectral type, star-exoplanet separation, and planet atmosphere basic parameters, and (ii) delineating a range of stellar, exoplanet, and atmospheric parameters for which photosynthetic activity might be feasible. In order to address these goals, we make use of a new metric, the absorption rate &gamma;, for the evaluation of the exoplanet photosynthetic activity that, based on state-of-the-art planet atmosphere and stellar photosphere spectroscopic models, quantifies the overlap between those models with the absorption spectra of photosynthetic pigments, both terrestrial and theoretical. We provide with a set of results for a combination of photosystems and exoplanetary environments revealing the importance of our metric when compared to previous photosynthesis indicators.

]]>Universe doi: 10.3390/universe8120623

Authors: Jafar Sadeghi Behnam Pourhassan Saeed Noori Gashti Elaheh Naghd Mezerji Antonio Pasqua

In this paper, we study the inflationary scenario in logarithmic f(R) gravity, where the rate of inflation roll is constant. On the other hand, our gravitational f(R) model is a polynomial plus a logarithmic term. We take advantage of constant-roll conditions and investigate the cosmic evolution of the logarithmic f(R) gravity. We present a numerical and a graphical study using the model parameters. Additionally, we obtain the corresponding potential by using the constant-roll condition. We obtain the exact value of the potential satisfying the constant-roll conditions. Next, we challenge it with refined swampland conjecture with respect to the Planck data. Finally, we compare our results with the latest observable data.

]]>Universe doi: 10.3390/universe8120622

Authors: Thorsten Chwalek Frédéric Déliot

The production of top quark pairs (tt&macr;) via the quark-antiquark initial state is not symmetric under the exchange of top quark and antiquark. Calculations of this next-to-leading order effect predict asymmetries of about one to a few percent, depending on the centre-of-mass energy and the selected phase space. Experimentally, this charge asymmetry of tt&macr; production manifests itself in differences in angular distributions between top quarks and antiquarks. Sensitive observables are the rapidities of the produced top quarks and antiquarks as well as their energies. In dileptonic tt&macr; events, the asymmetry of the tt&macr; system is reflected in a similar asymmetry in the system of the produced lepton pair, with the crucial advantage of a simpler reconstruction procedure. In this article we review the measurements of this effect in different final states and using different observables by the ATLAS and CMS Collaborations in LHC collisions at three different centre-of-mass energies.

]]>Universe doi: 10.3390/universe8120621

Authors: Jafar Sadeghi Mohammad Reza Alipour Saeed Noori Gashti

In this article, we want to check four inflation models, namely, composite NJL inflation (NJLI), Glueball inflation (GI), super Yang&ndash;Mills inflation (SYMI), and Orientifold inflation (OI), with two conjectures of the swampland program: scalar weak gravity conjecture (SWGC) and strong scalar weak gravity conjecture (SSWGC) since all these models violate the dS swampland conjecture (DSC) but are compatible with further refining de Sitter swampland conjecture (FRDSSC) through manual adjustment of free parameters of the mentioned conjecture. We want to study the simultaneous compatibility of each model with these two new conjectures. Despite being consistent with (FRDSSC), we find that all models are not compatible with the other conjectures of the Swampland program in all regions, and these conjectures are only satisfied in a specific area. Moreover, due to the presence of constant parameter (&#981;0) in the higher orders derivatives, the (SYMI) and (OI) among all the models are more compatible with all conjectures of the swampland program. These models can provide a more significant amount of satisfaction with all of them. They can be suitable and accurate inflation models for a more profound examination of universe developments. We determined a particular region for these models is compatible with (FRDSSC), (SWGC), and (SSWGC) simultaneously.

]]>Universe doi: 10.3390/universe8120620

Authors: Michele Maiorano Francesco De Paolis Achille A. Nucita

The standard technique for very low-frequency gravitational wave detection is mainly based on searching for a specific spatial correlation in the variation of the times of arrival of the radio pulses emitted by millisecond pulsars with respect to a timing model. This spatial correlation, which in the case of the gravitational wave background must have the form described by the Hellings and Downs function, has not yet been observed. Therefore, despite the numerous hints of a common red noise in the timing residuals of many millisecond pulsars compatible with that expected for the gravitational wave background, its detection has not yet been achieved. By now, the reason is not completely clear and, from some recent works, the urgency to adopt new detection techniques, possibly complementary to the standard one, is emerging clearly. Of course, this demand also applies to the detection of continuous gravitational waves emitted by supermassive black hole binaries populating the Universe. In the latter case, important information could, in principle, emerge from the millisecond pulsars considered individually in a single-pulsar search of continuous GWs. In this context, the surfing effect can then be exploited, helping to select the best pulsars to carry out such analysis. This paper aims to clarify when the surfing effect occurs and describe it exhaustively. A possible application to the case of the supermassive black hole binary candidate PKS 2131&ndash;021 and millisecond pulsar J2145&ndash;0750 is also analyzed.

]]>Universe doi: 10.3390/universe8120619

Authors: Brynmor Haskell Marco Antonelli Pierre Pizzochero

We investigate the effect of a pinned superfluid component on the gravitational wave emissions of a rotating neutron star. The pinning of superfluid vortices to the flux-tubes in the outer core (where the protons are likely to form a type-II superconductor) is a possible mechanism to sustain long-lived and non-axisymmetric neutron currents in the interior, which break the axial symmetry of the unperturbed hydrostatic configuration. We consider pinning-induced perturbations to a stationary corotating configuration and determine the upper limits on the strength of gravitational wave emissions due to the pinning of vortices with a strong toroidal magnetic field of the kind predicted by recent magneto-hydrodynamic simulations of neutron star interiors. We estimate the contributions to gravitational wave emissions from both the mass and current multipole generated by the pinned vorticity in the outer core and find that the mass quadrupole can be large enough for gravitational waves to provide the dominant spindown torque in millisecond pulsars.

]]>Universe doi: 10.3390/universe8120618

Authors: Wernhuar Tarng Yu-Chia Liao Kuo-Liang Ou

Einstein described the relationship between mass and energy using the theory of special relativity by a simple equation, E=mc2. Mass&ndash;energy equivalence implies that mass can be converted into energy and vice versa. In this study, a virtual reality (VR) system was developed for learners to take a spacecraft travelling at nearly the speed of light to conduct space exploration and understand the concepts of special relativity and mass&ndash;energy equivalence. A teaching experiment was conducted to investigate the learning effectiveness and cognitive load of learners by recruiting 60 students as research samples. The experimental group (30 students) used the VR system and the control group (30 students) used physics textbooks for learning special relativity and mass&ndash;energy equivalence. The experimental results reveal that the learning effectiveness of the experimental group is higher than that of the control group while the cognitive load of the former is lower than that of the latter. The questionnaire results show that students of the control group had responded positively to learning content, cognitive usefulness, cognitive ease of use, and user satisfaction, indicating that they were satisfied with the learning experience of the VR system.

]]>Universe doi: 10.3390/universe8120617

Authors: Georg Bergner Gernot Münster Stefano Piemonte

We review our efforts in investigating gauge theories with fermions in the adjoint representation of the gauge group by means of numerical simulations. These theories have applications in possible extensions of the standard model of particle physics, being a core part of supersymmetric gauge theories. They also play an important role in uncovering fundamental properties of strongly interacting theories due to distinct features, such as a substantially different phase diagram.

]]>Universe doi: 10.3390/universe8120616

Authors: C. R. Muniz H. R. Christiansen M. S. Cunha J. Furtado V. B. Bezerra

In this paper, we study quantum relativistic features of a scalar field around the Rindler&ndash;Schwarzschild wormhole. First, we introduce this new class of spacetime, investigating some energy conditions and verifying their violation in a region nearby the wormhole throat, which means that the object must have an exotic energy in order to prevent its collapse. Then, we study the behavior of the massless scalar field in this spacetime and compute the effective potential by means of tortoise coordinates. We show that such a potential is attractive close to the throat and that it is traversable via quantum tunneling by massive particles with sufficiently low energies. The solution of the Klein&ndash;Gordon equation is obtained subsequently, showing that the energy spectrum of the field is subject to a constraint, which induces a decreasing oscillatory behavior. By imposing Dirichlet boundary conditions on a spherical shell in the neighborhood of the throat we can determine the particle energy levels, and we use this spectrum to calculate the quantum revival of the eigenstates. Finally, we compute the Casimir energy associated with the massless scalar field at zero temperature. We perform this calculation by means of the sum of the modes method. The zero-point energy is regularized using the Epstein&ndash;Hurwitz zeta-function. We also obtain an analytical expression for the Casimir force acting on the shell.

]]>Universe doi: 10.3390/universe8120615

Authors: Thomas Thiemann Madhavan Varadarajan

A rigorous implementation of the Wheeler&ndash;Dewitt equations was derived in the context of Loop Quantum Gravity (LQG) and was coined Quantum Spin Dynamics (QSD). The Hamiltonian constraint of QSD was criticised as being too local and to prevent &ldquo;propagation&rdquo; in canonical LQG. That criticism was based on an algorithm developed for QSD for generating solutions to the Wheeler&ndash;DeWitt equations. The fine details of that algorithm could not be worked out because the QSD Hamiltonian constraint makes crucial use of the volume operator, which cannot be diagonalised analytically. In this paper, we consider the U(1)3 model for Euclidean vacuum LQG which consists of replacing the structure group SU(2) by U(1)3 and otherwise keeps all properties of the SU(2) theory intact. This enables analytical calculations and the fine details of the algorithm ingto be worked out. By considering one of the simplest possible non-trivial classes of solutions based on very small graphs, we show that (1) an infinite number of solutions ingexist which are (2) generically not normalisable with respect to the inner product on the space of spatially diffeomorphism invariant distributions and (3) generically display propagation. Due to the closeness of the U(1)3 model to Euclidean LQG, it is extremely likely that all three properties hold also in the SU(2) case and even more so in physical Lorentzian LQG. These arguments can in principle be made water tight using modern numerical (e.g., ML or QC) methods combined with the techniques developed in this paper which we reserve for future work.

]]>Universe doi: 10.3390/universe8120614

Authors: Ming Yang

The Kepler space telescope has detected a large number of variable stars. We summarize 2261 &delta; Scuti and hybrid variables in the literature, and perform time-frequency analysis on these variable stars. Two non-eclipsing binary systems, KIC 5080290 and KIC 5480114, are newly discovered. They both pass more detailed aperture photometry and bright star contamination checks. The results of the time-frequency analysis demonstrate that the companions are stellar objects with orbital periods of approximately 265 days and 445 days, respectively. The orbital parameters of the two systems and the lower mass limits of the companions are obtained. The primary stars of both systems are slightly evolved intermediate-mass stars. The detection of intermediate-mass binary stars is helpful to understand the formation and evolution mechanism of binary stars in this mass region.

]]>Universe doi: 10.3390/universe8120612

Authors: Gavin P. Lamb Lorenzo Nativi Stephan Rosswog D. Alexander Kann Andrew Levan Christoffer Lundman Nial Tanvir

Using the resultant profiles from 3D hydrodynamic simulations of relativistic jets interacting with neutron star merger wind ejecta, we show how the inhomogeneity of energy and velocity across the jet surface profile can alter the observed afterglow lightcurve. We find that the peak afterglow flux depends sensitively on the observer&rsquo;s line-of-sight, not only via the jet inclination but also through the jet rotation: for an observer viewing the afterglow within the GRB-bright jet core, we find a peak flux variability on the order &lt;0.5 dex through rotational orientation and &lt;1.3 dex for the polar inclination. An observed afterglow&rsquo;s peak flux can be used to infer the jet kinetic energy, and where a top-hat jet is assumed, we find the range of inferred jet kinetic energies for our various model afterglow lightcurves (with fixed model parameters), covers &sim;1/3 of the observed short GRB population. Additionally, we present an analytic jet structure function that includes physically motivated parameter uncertainties due to variability through the rotation of the source. An approximation for the change in collimation due to the merger ejecta mass is included and we show that by considering the observed range of merger ejecta masses from short GRB kilonova candidates, a population of merger jets with a fixed intrinsic jet energy is capable of explaining the observed broad diversity seen in short GRB afterglows.

]]>Universe doi: 10.3390/universe8120613

Authors: Moncef Derouich Saleh Qutub Fainana Mustajab Badruddin Zaheer Ahmad

In solar and stellar atmospheres, atomic excitation by impact with electrons plays an important role in the formation of spectral lines. We make use of available experimental and theoretical cross-sections to calculate the excitation rates in s&ndash;p transitions of alkali and alkaline atoms through collisions with electrons. Then, we infer a general formula for calculating the excitation rates by using genetic programming numerical methods. We propose an extension of our approach to deduce collisional excitation rates for complex atoms and atoms with hyperfine structure. Furthermore, the developed method is also applied to determine collisional polarization transfer rates. Our results are not specific to a given atom and can be applied to any s&ndash;p atomic transition. The accuracy of our results is discussed.

]]>Universe doi: 10.3390/universe8120611

Authors: Liudmila S. Rakhmanova Maria O. Riazantseva Georgy N. Zastenker Yuri I. Yermolaev

The Earth&rsquo;s magnetosphere is permanently influenced by the solar wind. When supersonic and superalfvenic plasma flow interacts with the magnetosphere, the magnetosheath region is formed, which is filled with shocked turbulent plasma. Varying SW parameters influence the mechanisms of formation of this boundary layer, including the dynamics of turbulence behind the bow shock. The effect of the solar wind on the development of turbulence in the magnetosheath was demonstrated recently based on broad statistics of spacecraft measurements. The present study considers the multipoint observations of turbulent fluctuations in the solar wind, in the dayside magnetosheath and at the flanks, to analyze the evolution of the turbulent cascade while the solar wind plasma enters the magnetosheath. Observations of the magnetosheath behind the quasi-perpendicular bow shock are analyzed to exclude the influence of the bow shock topology from consideration. Three basic types of solar wind flows are considered: slow undisturbed solar wind, compressed regions, and interplanetary manifestations of coronal mass ejections. The results show surviving Kolmogorov scaling behind the bow shock for steady solar wind flow and amplification of the compressive fluctuations at the kinetic scales at the magnetosheath flanks for the solar wind associated with compressed plasma streams. During interplanetary manifestations of the coronal mass ejection, the spectra in the dayside magnetosheath substantially deviate from those observed in the solar wind (including the absence of Kolmogorov scaling and steepening at the kinetic scales) and restore at the flanks.

]]>Universe doi: 10.3390/universe8120610

Authors: Giuseppe Consolini Paola De Michelis Tommaso Alberti Igino Coco Fabio Giannattasio Michael Pezzopane Roberta Tozzi

Complexity is a typical feature of space plasmas that may involve the formation of multiscale coherent magnetic and plasma structures. The winding features (pseudo-polarization) of magnetic field fluctuations at different spatial scales are a useful quantity in this framework for investigating complexity in space plasma. Indeed, a strong link between pseudo-polarization, magnetic/plasma structures, turbulence and dissipation exists. We present some preliminary results on the link between the polarization of the magnetic field fluctuations and the structure of field-aligned currents in the high-latitude ionosphere. This study is based on high-resolution (50 Hz) magnetic field data collected on board the European Space Agency Swarm constellation. The results show the existence of a clear link between the multiscale coarse-grained structure of pseudo-polarization and intensity of the field-aligned currents, supporting the recent findings according to which turbulence may be capable of generating multiscale filamentary current structures in the auroral ionosphere. This feature is also examined theoretically, along with its significance for the rate of energy deposition and heating in the polar regions.

]]>Universe doi: 10.3390/universe8110609

Authors: Nuno Filipe Castro Kirill Skovpen

A study of the top-quark interactions via flavour-changing neutral current (FCNC) processes provides an intriguing connection between the heaviest elementary particle of the standard model (SM) of particle physics and the new scalar bosons that are predicted in several notable SM extensions. The production cross sections of the processes with top-scalar FCNC interactions can be significantly enhanced to the observable level at the CERN Large Hadron Collider. The present review summarises the latest experimental results on the study of the top-quark interactions with the Higgs boson via an FCNC and describes several promising directions to look for new scalar particles.

]]>Universe doi: 10.3390/universe8110608

Authors: Antonio Gallerati Matteo Luca Ruggiero Lorenzo Iorio

Many exoplanets have been detected by the radial velocity method, according to which the motion of a binary system around its center of mass can produce a periodical variation of the Doppler effect of the light emitted by the host star. These variations are influenced by both Newtonian and non-Newtonian perturbations to the dominant inverse-square acceleration; accordingly, exoplanetary systems lend themselves to testing theories of gravity alternative to general relativity. In this paper, we consider the impact of the Standard Model Extension (a model that can be used to test all possible Lorentz violations) on the perturbation of radial velocity and suggest that suitable exoplanets&rsquo; configurations and improvements in detection techniques may contribute to obtaining new constraints on the model parameters.

]]>Universe doi: 10.3390/universe8110607

Authors: Frank M. Rieger

Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic experimental findings by recent instruments, and discusses possible interpretations and astrophysical constraints on source energetics. Particular attention is given to potential sites and mechanisms of UHECR acceleration in AGNs, including gap-type particle acceleration close to the black hole, as well as first-order Fermi acceleration at trans-relativistic shocks and stochastic shear particle acceleration in large-scale jets. It is argued that the last two represent the most promising mechanisms given our current understanding, and that nearby FR I type radio galaxies provide a suitable environment for UHECR acceleration.

]]>Universe doi: 10.3390/universe8110606

Authors: Fabio Bellini Claudia Tomei

The present Special Issue is dedicated to the long-sought-after nuclear process known as Neutrinoless Double Beta Decay (NDBD), a nuclear transition characterized by the simultaneous decay of two neutrons into protons and electrons, without the emission of neutrinos [...]

]]>Universe doi: 10.3390/universe8110605

Authors: Ming-Xian Zhao Gui-Ming Le Yong-Hua Liu

There were 51 superactive regions (SARs) during solar cycles (SCs) 21&ndash;24. We divided the SARs into SARs1, which produced extreme space weather events including &ge;X5.0 flares, ground level events (GLEs), and super geomagnetic storms (SGSs, Dst &lt; &minus;250 nT), and SARs2, which did not produce extreme space weather events. The total number of SARs1 and SARs2 are 31 and 20, respectively. The statistical results showed that 35.5%, 64.5%, and 77.4% of the SARs1 appeared in the ascending phase, descending phase, and in the period from two years before to the three years after the solar maximum, respectively, whereas 50%, 50%, and 100% of the SARs2 appeared in the ascending phase, descending phase, and in the period from two years before to the three years after the solar maximum, respectively. The total number of SARs during an SC has a good association with the SC amplitude, implying that an SC with a higher amplitude will have more SARs than that with a lower amplitude. However, the largest flare index of a SAR within an SC has a poor association with the SC amplitude, suggesting that a weak cycle may have a SAR that may produce a series of very strong solar flares. The analysis of the north&ndash;south asymmetry of the SARs showed that SARs1 dominated in the southern hemisphere of the sun during SCs 21&ndash;24. The SAR2 dominated in the different hemispheres by turns for different SCs. The solar flare activities caused by the SARs with source locations in the southern hemisphere of the sun were much stronger than those caused by the SARs with source locations in the northern hemisphere of the sun during SCs 21&ndash;24.

]]>Universe doi: 10.3390/universe8110603

Authors: Swastik Bhattacharya S. Shankaranarayanan

Black hole horizons interact with external fields when matter or energy falls through them. Such non-stationary black hole horizons can be described using viscous fluid equations. This work attempts to describe this process using effective field theory methods. Such a description can provide important insights beyond classical black hole physics. In this work, we construct a low-energy effective field theory description for the horizon-fluid of a 4-dimensional, asymptotically flat, Einstein black hole. The effective field theory of the dynamical horizon has two ingredients: degrees of freedom involved in the interaction with external fields and symmetry. The dual requirements of incorporating near-horizon symmetries (S1 diffeomorphism) and possessing length scales due to external perturbations are naturally satisfied if the theory on the non-stationary black hole horizon is a deformed Conformal Field Theory (CFT). For the homogeneous external perturbations, at the lowest order, this leads to a (2+1)-dimensional massive scalar field where the mass is related to the extent of the deformation of the CFT. We determine the mass by obtaining the correlation function corresponding to the effective field and relating it to the bulk viscosity of the horizon-fluid. Additionally, we show that the coefficient of bulk viscosity of the horizon-fluid determines the time required for black holes to scramble. Furthermore, we argue that matter-field modes with energy less than meff falling into the horizon thermalize more slowly. Finally, we construct a microscopic toy model for the horizon-fluid that reduces to the effective field theory with a single scalar degree of freedom. We then discuss the usefulness of the effective field model in understanding how information escapes from a black hole at late times.

]]>Universe doi: 10.3390/universe8110604

Authors: Xianglong Wu Xiangdong Zhang

The correspondence between the shadow radius and the real part of the quasinormal modes (QNMs) of a Kerr&ndash;Sen black hole is studied. By using the equation of the shadow radius of Kerr&ndash;Sen black hole and the angular separation constant of the QNMs, the expression of QNMs related to shadow radius is established in the eikonal limit. We found that, our formula can reduce to the previous result of Kerr black hole when Kerr-Sen parameter b sets to zero.

]]>Universe doi: 10.3390/universe8110602

Authors: Tianshu Qin Sarah V. Badman Joe Kinrade Alexander Bader

We examined Hubble Space Telescope images of Saturn&rsquo;s northern UV aurora in 2013&ndash;2017, identified 29 short-lived flashes, and examined simultaneous magnetometer data collected by the Cassini orbiter. When observation cadence permitted, a flash lifetime of 4&ndash;17 min (subject to exposure time-related uncertainties), and a 40&ndash;70 min recurrence period were found. An occurrence map shows a strong preference in both local time (14&ndash;19 LT) and latitude (75&ndash;85&deg;). These transient flashes are identified in both the presence and absence of Saturn&rsquo;s main auroral oval, indicating the lack of dependence on the main emission power. The concurrent magnetic field pulsations generally form a sawtooth shape, and the local field strength experiences a change of 0.2 to 2.0 nT (depending on the distance of Cassini). The quasiperiodic pulsation events were all detected when the spacecraft was in the southern hemisphere with conjugate flashes in northern aurora, suggesting these events occur on closed field lines, and typically showing a sudden transition to a less lagging, more southward magnetic field configuration. We also found the ionospheric footprint of the spacecraft must be close to the region of flashes for magnetic field pulsations to be detected, implying a localised rather than global driving process.

]]>Universe doi: 10.3390/universe8110601

Authors: Christian Käding Mario Pitschmann

We provide a description of interacting quantum fields in terms of density matrices for any occupation numbers in Fock space in a momentum basis. As a simple example, we focus on a real scalar field interacting with another real scalar field, and present a practicable formalism for directly computing the density matrix elements of the combined scalar&ndash;scalar system. For deriving the main formula, we use techniques from non-equilibrium quantum field theory like thermo-field dynamics and the Schwinger&ndash;Keldysh formalism. Our results allow for studies of particle creation/annihilation processes at finite times and other non-equilibrium processes, including those found in the theory of open quantum systems.

]]>Universe doi: 10.3390/universe8110600

Authors: Tom Banks Willy Fischler

The holographic space-time (HST) model of inflation has a potential explanation for dark matter as tiny primordial black holes. Motivated by a recent paper of Barrau, we propose a version of this model where some of the inflationary black holes (IBHs), whose decay gives rise to the Hot Big Bang, carry the smallest value of a discrete symmetry charge. The fraction f of IBHs carrying this charge is difficult to estimate from first principles, but we determine it by requiring that the crossover between radiation and matter domination occurs at the correct temperature Teq&sim;1eV=10&minus;28MP. The fraction is small, f&sim;2&times;10&minus;9, so we believe this gives an extremely plausible model of dark matter.

]]>Universe doi: 10.3390/universe8110599

Authors: Wajiha Javed Hafsa Irshad Reggie C. Pantig Ali Övgün

This paper is devoted to computing the weak deflection angle for the Kalb&ndash;Ramond traversable wormhole solution in plasma and dark matter mediums by using the method of Gibbons and Werner. To acquire our results, we evaluate Gaussian optical curvature by utilizing the Gauss&ndash;Bonnet theorem in the weak field limits. We also investigate the graphical influence of the deflection angle &alpha;&tilde; with respect to the impact parameter &sigma; and the minimal radius r0 in the plasma medium. Moreover, we derive the deflection angle by using a different method known as the Keeton and Petters method. We also examine that if we remove the effects of plasma and dark matter, the results become identical to that of the non-plasma case.

]]>Universe doi: 10.3390/universe8110598

Authors: Nikola Paunković Marko Vojinović

We give a general overview of various flavours of the equivalence principle in classical and quantum physics, with special emphasis on the so-called weak equivalence principle, and contrast its validity in mechanics versus field theory. We also discuss its generalisation to a theory of quantum gravity. Our analysis suggests that only the strong equivalence principle can be considered fundamental enough to be generalised to a quantum gravity context since all other flavours of equivalence principle hold only approximately already at the classical level.

]]>Universe doi: 10.3390/universe8110597

Authors: Herondy F. S. Mota Celio R. Muniz Valdir B. Bezerra

In the present paper, we investigate thermal fluctuation corrections to the vacuum energy at zero temperature of a conformally coupled massless scalar field, whose modes propagate in the Einstein universe with a spherical boundary, characterized by both Dirichlet and Neumann boundary conditions. Thus, we generalize the results found in the literature in this scenario, which has considered only the vacuum energy at zero temperature. To do this, we use the generalized zeta function method plus Abel-Plana formula and calculate the renormalized Casimir free energy as well as other thermodynamics quantities, namely, internal energy and entropy. For each one of them, we also investigate the limits of high and low temperatures. At high temperatures, we found that the renormalized Casimir free energy presents classical contributions, along with a logarithmic term. Also in this limit, the internal energy presents a classical contribution and the entropy a logarithmic term, in addition to a classical contribution as well. Conversely, at low temperatures, it is demonstrated that both the renormalized Casimir free energy and internal energy are dominated by the vacuum energy at zero temperature. It is also demonstrated that the entropy obeys the third law of thermodynamics.

]]>Universe doi: 10.3390/universe8110596

Authors: Fang Wen Wenyuan Cui Miao Tian Xiaoxiao Zhang Jianrong Shi Bo Zhang

Based on the spectra with high resolution and a high signal-to-noise ratio, we investigate the enrichment history of the s-process element in seven barium (Ba) stars by measuring their Ba odd isotope fraction. It is found that the relative contributions of the s-process to their Ba abundance are 91.4&plusmn;25.7%, 91.4&plusmn;34.3%, 82.9&plusmn;28.5%, 77.1&plusmn;31.4%, and 71.4&plusmn;37.1% for REJ 0702+129, HD 13611, BD+80&deg;670, HR 5692, and HD 202109, respectively. Our results suggest that these five Ba stars have a prominent s-process signature, which indicates that their heavy elements mainly come from their former AGB companions (now WDs) by mass transfer, while the r-process contribution can naturally be explained by the evolution of the Milky Way. The s-process contribution of BD+80&deg;670 is 51.4&plusmn;31.4%, which is the lowest among our seven sample stars. Considering its lower values of both [Ba/Nd] and [Ba/Eu], we suspect that BD+68&deg;1027 is likely to be a r-rich Ba star and has similar origins to the CEMP-r/s stars. HD 218356 has an unreasonable s-process contribution over 100%. Combining its stellar atmospheric parameters and the evolutionary stage, we speculate that HD 218356 is a more evolved extrinsic Ba star, and its massive companion should have the largest s-process efficiency in our samples.

]]>Universe doi: 10.3390/universe8110595

Authors: Zhizhi Chen Yanlin Li Sumanjit Sarkar Santu Dey Arindam Bhattacharyya

In this article, a Ricci soliton and *-conformal Ricci soliton are examined in the framework of trans-Sasakian three-manifold. In the beginning of the paper, it is shown that a three-dimensional trans-Sasakian manifold of type (&alpha;,&beta;) admits a Ricci soliton where the covariant derivative of potential vector field V in the direction of unit vector field &xi; is orthogonal to &xi;. It is also demonstrated that if the structure functions meet &alpha;2=&beta;2, then the covariant derivative of V in the direction of &xi; is a constant multiple of &xi;. Furthermore, the nature of scalar curvature is evolved when the manifold of type (&alpha;,&beta;) satisfies *-conformal Ricci soliton, provided &alpha;&ne;0. Finally, an example is presented to verify the findings.

]]>Universe doi: 10.3390/universe8110594

Authors: Asher Yahalom

In a previous paper we have shown that superluminal particles are allowed by the general relativistic theory of gravity provided that the metric is locally Euclidean. Here we calculate the probability density function of a canonical ensemble of superluminal particles as function of temperature. This is done for both space-times invariant under the Lorentz symmetry group, and for space times invariant under an Euclidean symmetry group. Although only the Lorentzian metric is stable for normal matter density, an Euclidian metric can be created under special gravitational circumstances and persist in a limited region of space-time consisting of the very early universe, which is characterized by extremely high densities and temperatures. Superluminal particles also allow attaining thermodynamic equilibrium at a shorter duration and suggest a rapid expansion of the matter density.

]]>Universe doi: 10.3390/universe8110593

Authors: Yunqi Sun Jianfeng Zhou

The sampling effect of the imaging acquisition device is an integration of the input signal within the pixel, resulting in an additional error in the pixel value. Additionally, a sampler with asymmetric intra-pixel quantum efficiency leads to position errors in high-precision astrometry. This paper proposes a model for the integral sampling process. An algorithm that solves the sampling effect, as well as the position error with high accuracy, is also provided. This algorithm provides an accuracy increase of 106 for Gaussian images with a uniform integral sampler. The accuracy limit of the Gaussian image comes from the truncation error. Also, this algorithm provides about 4 times accuracy improvement by eliminating the systematic error caused by the integral sampler with asymmetric intra-pixel quantum efficiency.

]]>Universe doi: 10.3390/universe8110592

Authors: Hamood Ur Rehman Aziz Ullah Awan ElSayed M. Tag-ElDin Uzma Bashir Seham Ayesh Allahyani

In this paper, the extended simple equation method (ESEM) and the generalized Riccati equation mapping (GREM) method are applied to the nonlinear third-order Gilson&ndash;Pickering (GP) model to obtain a variety of new exact wave solutions. With the suitable selection of parameters involved in the model, some familiar physical governing models such as the Camassa&ndash;Holm (CH) equation, the Fornberg&ndash;Whitham (FW) equation, and the Rosenau&ndash;Hyman (RH) equation are obtained. The graphical representation of solutions under different constraints shows the dark, bright, combined dark&ndash;bright, periodic, singular, and kink soliton. For the graphical representation, 3D plots, contour plots, and 2D plots of some acquired solutions are illustrated. The obtained wave solutions motivate researchers to enhance their theories to the best of their capacities and to utilize the outcomes in other nonlinear cases. The executed methods are shown to be practical and straightforward for approaching the considered equation and may be utilized to study abundant types of NLEEs arising in physics, engineering, and applied sciences.

]]>Universe doi: 10.3390/universe8110591

Authors: Sergey Bogovalov Maxim Petrov

Computer modeling of the outflow from Be stars is performed. In our approach, processes of turbulence excitation and turbulent viscosity are added to the conventional model of the radiation driven winds. The objective of our study is to reproduce from the first principles the main features of the outflow from Be stars: a fast polar wind and a slow viscous Keplerian disk at the equator. At sub-critical velocity of rotation up to 0.999 of the critical velocity, our model reproduces the formation of the fast polar wind together with a slow highly turbulent outflow at the equatorial region. This outflow, however, does not reassemble a Keplerian disk. We link this to the absence of the angular moment transfer from the star to the disk. This process provides an increase of the angular momentum of the disk matter with radius. We consider a star with super critical rotation as the simplest way to supply the angular momentum to the disk. In this case, the star surface has a higher azimuthal speed than the matter at the inner edge of the disk. The angular momentum transfer becomes unavoidable. Already at rotation velocity 0.5% above the critical one, a quasi Keplerian disk at the equator is formed with size &sim;10 stellar radius. At rotation 1% higher than the critical speed, the disk reaches &sim;15 stellar radius. The main conclusion following from our work is that the conventional model of the radiation driven winds is able to reproduce the main features of the outflow from Be stars provided that the process of turbulence excitation and a process of angular momentum supply of the disk from the central source are added in to this model.

]]>Universe doi: 10.3390/universe8110590

Authors: Ahmed Hussein M. A. Mahmoud Ayman A. Aly M. N. El-Hammamy Yasser Mohammed

Nuclear matter, at sufficiently energy density and high temperature, undergoes a transition to a state of strongly interacting QCD matter in which quarks and gluons are not confined known as the Quark&ndash;Gluon Plasma (QGP). QGP is usually produced in high-energy collisions of heavy nuclei in the laboratory, where an enhancement of strange hadrons&rsquo; production is observed. Many of the effects which are typical of heavy ion phenomenology have been observed in high-multiplicity proton&ndash;proton (pp) collisions. The enhancement of strange particles&rsquo; production in pp collisions was reported at s=7 TeV and s=13 TeV in 2017 and 2020, respectively, and it was found that the integrated yields of strange particles, relative to pions, increase notably with the charged-particle multiplicity of events. Here, we report the multiplicity dependence of strange particles at |y|&lt;0.5 in pp collisions at s = 7 TeV, 13 TeV, 20 TeV, and 27 TeV from a Monte Carlo simulation using PYTHIA8, EPOS-LHC, and Herwig7.

]]>Universe doi: 10.3390/universe8110589

Authors: Giovanni Gandolfi Andrea Lapi Tommaso Ronconi Luigi Danese

We exploit the recent determination of the cosmic star formation rate (SFR) density at high redshifts z&#8819;4 to derive astroparticle constraints on three common dark matter (DM) scenarios alternative to standard cold dark matter (CDM): warm dark matter (WDM), fuzzy dark matter (&psi;DM) and self-interacting dark matter (SIDM). Our analysis relies on the ultraviolet (UV) luminosity functions measured from blank field surveys by the Hubble Space Telescope out to z&#8818;10 and down to UV magnitudes MUV&#8818;&minus;17. We extrapolate these to fainter yet unexplored magnitude ranges and perform abundance matching with the halo mass functions in a given DM scenario, thus, obtaining a redshift-dependent relationship between the UV magnitude and the halo mass. We then computed the cosmic SFR density by integrating the extrapolated UV luminosity functions down to a faint magnitude limit MUVlim, which is determined via the above abundance matching relationship by two free parameters: the minimum threshold halo mass MHGF for galaxy formation, and the astroparticle quantity X characterizing each DM scenario (namely, particle mass for WDM and &psi;DM, and kinetic temperature at decoupling TX for SIDM). We perform Bayesian inference on such parameters using a Monte Carlo Markov Chain (MCMC) technique by comparing the cosmic SFR density from our approach to the current observational estimates at z&#8819;4, constraining the WDM particle mass to mX&asymp;1.2&minus;0.4(&minus;0.5)+0.3(11.3) keV, the &psi;DM particle mass to mX&asymp;3.7&minus;0.4(&minus;0.5)+1.8(+12.9.3)&times;10&minus;22 eV, and the SIDM temperature to TX&asymp;0.21&minus;0.06(&minus;0.07)+0.04(+1.8) keV at 68% (95%) confidence level. Finally, we forecast how such constraints will be strengthened by upcoming refined estimates of the cosmic SFR density if the early data on the UV luminosity function at z&#8819;10 from the James Webb Space Telescope (JWST) will be confirmed down to ultra-faint magnitudes.

]]>Universe doi: 10.3390/universe8110588

Authors: Xiao-Hong Zhao Kang-Fa Cheng

We study the gamma-ray burst (GRB) afterglow light curves produced by an off-axis jet in a stratified circumburst medium and summarize the temporal indices of the coasting phase, the deceleration phase, the Newtonian phase, and the deep Newtonian phase for various viewing angles and power-law indices of medium density. Generally, the afterglow light curves of off-axis GRBs in the homogeneous interstellar medium have a steep rise arising due to jet deceleration. In the stratified medium, the flux rises is more shallow but peaks earlier for the same viewing angle due to faster deceleration of the jet running into the denser stratified medium, compared with the case of the interstellar medium (ISM). Observations of off-axis bursts will possibly increase over the coming years due to the arrival of the multi-messenger era and the forthcoming surveys in multiple bands. The temporal indices of off-axis afterglows derived in the paper will provide a reference for comparison with the observations and can diagnose the circumburst environment. The numerical code calculating the afterglow light curve also can be used to fit the multi-wavelength light curves.

]]>Universe doi: 10.3390/universe8110587

Authors: Luigi Foschini Matthew L. Lister Heinz Andernach Stefano Ciroi Paola Marziani Sonia Antón Marco Berton Elena Dalla Bontà Emilia Järvelä Maria J. M. Marchã Patrizia Romano Merja Tornikoski Stefano Vercellone Amelia Vietri

We considered the fourth catalog of gamma-ray point sources produced by the Fermi Large Area Telescope (LAT) and selected only jetted active galactic nuclei (AGN) or sources with no specific classification, but with a low-frequency counterpart. Our final list is composed of 2980 gamma-ray point sources. We then searched for optical spectra in all the available literature and publicly available databases, to measure redshifts and to confirm or change the original LAT classification. Our final list of gamma-ray emitting jetted AGN is composed of BL Lac Objects (40%), flat-spectrum radio quasars (23%), misaligned AGN (2.8%), narrow-line Seyfert 1, Seyfert, and low-ionization nuclear emission-line region galaxies (1.9%). We also found a significant number of objects changing from one type to another, and vice versa (changing-look AGN, 1.1%). About 30% of gamma-ray sources still have an ambiguous classification or lack one altogether.

]]>Universe doi: 10.3390/universe8110586

Authors: Ilya L. Shapiro

We present detailed pedagogical derivation of covariant derivative of fermions and some related expressions, including commutator of covariant derivatives and energy-momentum tensor of a free Dirac field. On top of that, local conformal transformations for a Dirac fermion in curved spacetime are considered and we obtain the expression for the energy-momentum tensor on the cosmological background.

]]>Universe doi: 10.3390/universe8110585

Authors: Yaru Feng Shaoming Hu Ruixin Zhou Songbo Gao

The origin of gamma-ray flares of blazars is still an open issue in jet physics. In this work, we reproduce the multiwavelength spectral energy distribution (SED) of flat-spectrum radio quasars 3C 454.3 under a one-zone leptonic scenario, investigate the variation of the physical parameters in different activity states, and analyze the possible origin of its &gamma;-ray outburst. Based on the analysis of multiwavelength quasi-simultaneous observations of 3C 454.3 during MJD 55,400&ndash;56,000, we consider that the radiation includes synchrotron (Syn), synchrotron self-Compton (SSC), and external Compton (EC) radiations by the simulation, and the seed photons of the external Compton component mainly comes from the broad-line region and dusty molecular torus. The model results show that: (1) We can well reproduce the multiwavelength quasi-simultaneity SED of 3C 454.3 in various activity states by using a one-zone Syn+SSC+EC model. (2) By comparing the physical model parameters of the bright and the quiescent states, we suggest that this &gamma;-ray flaring activity is more likely to be caused by the increase in the doppler factor.

]]>Universe doi: 10.3390/universe8110584

Authors: Neslihan Ozdemir Aydin Secer Muslum Ozisik Mustafa Bayram

In this scientific research article, the new Kudryashov method and the tanh-coth method, which have not been applied before, are employed to construct analytical and soliton solutions of the (2+1)-dimensional Hirota&ndash;Maccari system. The (2+1)-dimensional Hirota&ndash;Maccari system is a special kind of nonlinear Schr&ouml;dinger equation (NLSEs) that models the motion of isolated waves localized in a small part of space, and is used in such various fields as fiber optics telecommunication systems, nonlinear optics, plasma physics, and hydrodynamics. In addition, the Hirota&ndash;Maccari system defines the dynamical characters of femtosecond soliton pulse propagation in single-mode fibers. Analytical solutions of the model are successfully acquired with the assistance of symbolic computation utilizing these methods. Finally, 3D, 2D, and contour graphs of solutions are depicted at specific values of parameters. It is shown that the new Kudryashov method and the tanh-coth method are uncomplicated, very effective, easily applicable, reliable, and indeed vital mathematical tools in solving nonlinear models.

]]>Universe doi: 10.3390/universe8110583

Authors: Thomas Buchert Ismael Delgado Gaspar Jan Jakub Ostrowski

The Newtonian Lagrangian perturbation theory is a widely used framework to study structure formation in cosmology in the nonlinear regime. We review a general-relativistic formulation of such a perturbation approach, emphasizing results on an already developed extensive formalism including among other aspects: the non-perturbative modeling of Ricci and Weyl curvatures, gravitational waves, and pressure-supported fluids. We discuss subcases of exact solutions related to Szekeres Class II and, as an exact average model, Ricci-flat LTB models. The latter forms the basis of a generalization that we then propose in terms of a scheme that goes beyond the relativistic Lagrangian perturbation theory on a global homogeneous-isotropic background cosmology. This new approximation does not involve a homogeneous reference background and it contains Szekeres class I (and thus general LTB models) as exact subcases. Most importantly, this new approximation allows for the interaction of structure with an evolving &ldquo;background cosmology&rdquo;, conceived as a spatial average model, and thus includes cosmological backreaction.

]]>Universe doi: 10.3390/universe8110582

Authors: Nikolai N. Shchechilin Nikita A. Zemlyakov Andrey I. Chugunov Mikhail E. Gusakov

Nuclear pasta phases in the neutron stars mantle can affect the mechanical and transport properties of superdense matter, thus playing an important role in the dynamics and evolution of neutron stars. In this paper, we compare results obtained by the Extended Thomas&ndash;Fermi (ETF) method with the compressible liquid drop model (CLDM), based on the thermodynamically consistent description of the surface properties calculated for the two-phase plane interface and the same energy-density functional (for numerical illustration, we applied the Skyrme-type functional SLy4). Our ETF calculations found that pasta phases in cylindrical form cover a significant crustal region (both normal and inverse phases, aka spaghetti and bucatini are presented). Meanwhile, within the applied CLDM framework, which includes the thermodynamically required effect of neutron adsorption on the cluster&rsquo;s surface but neglects curvature corrections, only the spaghetti phase was found to be energetically favorable in the small density range prior to crust&ndash;core transition. On the other hand, the recent CLDM of Dinh Thi et al., 2021, which, on the contrary, accounts for curvature term but neglects neutron adsorption, predicts pasta phase onset in better agreement with the ETF. This fact highlights the importance of the curvature effects and allows counting on the potential validity of the CLDMs as a convenient, transparent and accurate tool for investigation of the pasta-phase properties.

]]>Universe doi: 10.3390/universe8110581

Authors: Koushik Chakraborty Farook Rahaman Saibal Ray Banashree Sen Debabrata Deb

We explore wormhole geometry in spiral galaxies under the third order Lovelock gravity. Using the cubic spline interpolation technique, we find the rotational velocity of test particles in the halo region of our spiral galaxy from observed values of radial distances and rotational velocities. Taking this value of the rotational velocity, we are able to show that it is possible to present a mathematical model regarding viable existence of wormholes in the galactic halo region of the Milky Way under the Lovelock gravity. A very important result that we obtain from the present investigation is that galactic wormhole in the halo region can exist with normal matter as well as exotic matter.

]]>Universe doi: 10.3390/universe8110580

Authors: Marcello Rotondo

The equation for canonical gravity produced by Wheeler and DeWitt in the late 1960s still presents difficulties both in terms of its mathematical solution and its physical interpretation. One of these issues is, notoriously, the absence of an explicit time. In this short note, we suggest one simple and straightforward way to avoid this occurrence. We go back to the classical equation that inspired Wheeler and DeWitt (namely, the Hamilton&ndash;Jacobi&ndash;Einstein equation) and make explicit, before quantization, the presence of a known, classically meaningful notion of time. We do this by allowing Hamilton&rsquo;s principal function to be explicitly dependent on this time locally. This choice results in a Wheeler&ndash;DeWitt equation with time. A working solution for the de Sitter minisuperspace is shown.

]]>Universe doi: 10.3390/universe8110579

Authors: The Pierre Auger Collaboration The Pierre Auger Collaboration

The Pierre Auger Observatory, which is the largest air-shower experiment in the world, offers unprecedented exposure to neutral particles at the highest energies. Since the start of data collection more than 18 years ago, various searches for ultra-high-energy (UHE, E&#8819;1017eV) photons have been performed, either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events such as gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory.

]]>Universe doi: 10.3390/universe8110578

Authors: Kiran Wani Haritma Gaur

We present a study of the flux distribution of a sample of 15 Intermediate and Low-energy peaked blazars using XMM-Newton observations in a total of 57 epochs on short-term timescales. We characterise the X-ray variability of all of the light curves using excess fractional variability amplitude and found that only 24 light curves in 7 sources are significantly variable. In order to characterise the origin of X-ray variability in these blazars, we fit the flux distributions of all these light curves using Gaussian and lognormal distributions, as any non-Gaussian perturbation could indicate the imprints of fluctuations in the accretion disc, which could be Doppler boosted through the relativistic jets in blazars. However, intra-day variability, as seen in our observations, is difficult to reconcile using disc components as the emissions in such sources are mostly dominated by jets. We used Anderson&ndash;Darling (AD) and &chi;2 tests to fit the histograms. In 11 observations of 4 blazars, namely, ON 231, 3C 273, PKS 0235+164 and PKS 0521-365, both models equally fit the flux distributions. In the rest of the observations, we are unable to model them with any distribution. In two sources, namely, BL Lacertae and S4 0954+650, the lognormal distribution is preferred over the normal distribution, which could arise from non-Gaussian perturbations from relativistic jets or linear Gaussian perturbation in the particle time scale leading to such flux distributions.

]]>Universe doi: 10.3390/universe8110577

Authors: Espen Gaarder Haug

This paper shows that a simple and relativistic extension of Newtonian gravity that takes into account Lorentz relativistic mass leads to predictions that fit supernova observations of magnitude versus redshift without the need to introduce dark energy. To test the concept, we look at 580 supernova data points from the Union2 database. Some relativistic extensions of Newtonian gravity have been investigated in the past, but we have reason to believe the efforts were rejected prematurely before their full potential was investigated. Our model suggests that mass, as related to gravity, is also affected by Lorentz relativistic effects, something that is not the case in standard gravity theory, and this adjustment gives supernova predictions that fit the observations. Our model seems very robust with respect to supernova data, as no arbitrary parameters are introduced. Since recent investigations of Lorentz&rsquo;s relativistic mass also seem to solve other challenges in physics, we think it is worthwhile for the physics community to look into this more carefully, at least before rejecting it based on prejudice. After all, no one has been able to detect dark energy despite massive efforts to do so. Until dark energy is really confirmed, other alternative models should be worth investigating further.

]]>Universe doi: 10.3390/universe8110576

Authors: Rui-Xin Yang Fei Xie Dao-Jun Liu

Unimodular gravity is a modified theory with respect to general relativity by an extra condition that the determinant of the metric is fixed. Especially, if the energy-momentum tensor is not imposed to be conserved separately, a new geometric structure will appear with potential observational signatures. In this paper, we study the tidal deformability of a compact star in unimodular gravity under the assumption of a non-conserved energy-momentum tensor. Both the electric-type and magnetic-type quadrupole tidal Love numbers are calculated for neutron stars using the polytrope model. It is found that the electric-type tidal Love numbers are monotonically increasing, but the magnetic-type ones are decreasing, with the increase in the non-conservation parameter. Compared with the observational data from the detected gravitational-wave events, a small negative non-conservation parameter is favored.

]]>Universe doi: 10.3390/universe8110575

Authors: Aghogho Ogwala Oluwole Johnson Oyedokun Olugbenga Ogunmodimu Andrew Ovie Akala Masood Ashraf Ali Punyawi Jamjareegulgarn Sampad Kumar Panda

Research on longitudinal discrepancies in local ionospheric variability, especially in equatorial and low-latitude regions, is a focal point of interest for the space weather modeling community. The ionosphere over these regions is influenced by complex electrodynamics, wind, and temperature dynamics that can seriously impact dynamic technological systems such as satellite tracking and positioning, satellite radio communication, and navigation control systems. Here, we researched the longitudinal variability in the ionospheric total electron content (TEC) by analyzing observed global positioning system (GPS)-derived TEC values along with those extracted from the most reliable global ionospheric maps (GIMs) and the International Reference Ionosphere (IRI-2016) model at selected stations in the vicinity of the magnetic equator along the American, African, and Asian longitude sectors. The period of study covered the descending (2016&ndash;2017) and deep solar minimum (2018&ndash;2019) years in the 24th solar cycle. Apart from the decreasing trend of the TEC from the descending to deep solar minimum period irrespective of season and longitude sector, the results showed a relatively higher magnitude of TEC in the African longitude than the other two longitude sectors. Despite evident overestimation and underestimations of TEC in both models, GIM predictions generally looked better in terms of observed variation patterns, especially in the African longitude. The study also highlights the seasonal and semiannual effects of longitudinal variations in TEC, manifesting in local time offsets and some peculiar anomalies, which seemed to be different from previously reported results, especially during the solar minimum years at the three longitude sectors. The insignificant effects of longitudinal variations on the equinoctial asymmetry are attributed to the diverse electron density distribution and ionospheric morphology at the three longitude sectors that will prompt further investigations in the future. The outcomes from this study may augment the past efforts of scientists to understand the seasonal effects of the longitudinal variations in TEC, thereby complementing the improvements of ionospheric representations in global ionosphere models and maps.

]]>Universe doi: 10.3390/universe8110574

Authors: Galina L. Klimchitskaya Vladimir M. Mostepanenko Vitaly B. Svetovoy

It is well known that the Casimir force calculated at large separations using the Lifshitz theory differs by a factor of 2 for metals described by the Drude or plasma models. We argue that this difference is entirely determined by the contribution of transverse electric (s) evanescent waves. Taking into account that there is a lack of experimental information on the electromagnetic response of metals to low-frequency evanescent waves, we propose an experiment on measuring the magnetic field of an oscillating magnetic dipole spaced in a vacuum above a thick metallic plate. According to our results, the lateral components of this field are governed by the transverse electric evanescent waves and may vary by orders of magnitude depending on the model describing the permittivity of the plates used in calculations and the oscillation frequency of the magnetic dipole. Measuring the lateral component of the magnetic field for typical parameters of the magnetic dipole designed in the form of a 1-mm coil, one could either validate or disprove the applicability of the Drude model as a response function of metal in the range of low-frequency evanescent waves. This will elucidate the roots of the Casimir puzzle lying in the fact that the theoretical predictions of the Lifshitz theory using the Drude model are in contradiction with the high-precision measurements of the Casimir force at separations exceeding 150 nm. Possible implications of the suggested experiment for a wide range of topics in optics and condensed matter physics dealing with evanescent waves are discussed.

]]>Universe doi: 10.3390/universe8110571

Authors: Vishva Patel Kauntey Acharya Parth Bambhaniya Pankaj S. Joshi

In this paper, the Penrose process is used to extract rotational energy from regular black holes. Initially, we consider the rotating Simpson&ndash;Visser regular spacetime, which describes the class of geometries of Kerr black hole mimickers. The Penrose process is then studied through conformally transformed rotating singular and regular black hole solutions. Both the Simpson&ndash;Visser and conformally transformed geometries depend on mass, spin, and an additional regularisation parameter l. In both cases, we investigate how the spin and regularisation parameter l affect the configuration of an ergoregion and event horizons. Surprisingly, we find that the energy extraction efficiency from the event horizon surface is not dependent on the regularisation parameter l in the Simpson&ndash;Visser regular spacetimes, and hence, it does not vary from that of the Kerr black hole. Meanwhile, in conformally transformed singular and regular black holes, we obtain that the efficiency rate of extracted energies is extremely high compared to that of the Kerr black hole. This distinct signature of conformally transformed singular and regular black holes is useful to distinguish them from Kerr black holes in observation.

]]>Universe doi: 10.3390/universe8110573

Authors: Rakesh Ranjan Sahoo Kamal Lochan Mahanta Saibal Ray

We obtain exact solutions to the field equations for five-dimensional locally rotationally symmetric (LRS) Bianchi type-I spacetime in the f(R,T) theory of gravity, where specifically, the following three cases are considered: (i) f(R,T)=&mu;(R+T), (ii) f(R,T)=R&mu;+RT&mu;2, and (iii) f(R,T)=R+&mu;R2+&mu;T, where R and T, respectively, are the Ricci scalar and trace of the energy&ndash;momentum tensor. It is found that the equation of state (EOS) parameter w is governed by the parameter &mu; involved in the f(R,T) expressions. We fine-tune the parameter &mu; to obtain the effect of phantom energy in the model. However, we also restrict this parameter to obtain a stable model of the universe.

]]>Universe doi: 10.3390/universe8110572

Authors: Michael L. Walker Steven Duplij

&ldquo;Selected topics in Gravity, Field Theory and Quantum Mechanics&rdquo; is for physicists wanting a fresh perspective into quantum gravity [...]

]]>Universe doi: 10.3390/universe8110570

Authors: Zhihui Xu Xiang Li Mingyang Cui Chuan Yue Wei Jiang Wenhao Li Qiang Yuan

Galactic cosmic rays are mostly made up of energetic nuclei, with less than 1% of electrons (and positrons). Precise measurement of the electron and positron component requires a very efficient method to reject the nuclei background, mainly protons. In this work, we develop an unsupervised machine learning method to identify electrons and positrons from cosmic ray protons for the Dark Matter Particle Explorer (DAMPE) experiment. Compared with the supervised learning method used in the DAMPE experiment, this unsupervised method relies solely on real data except for the background estimation process. As a result, it could effectively reduce the uncertainties from simulations. For three energy ranges of electrons and positrons, 80&ndash;128 GeV, 350&ndash;700 GeV, and 2&ndash;5 TeV, the residual background fractions in the electron sample are found to be about (0.45 &plusmn; 0.02)%, (0.52 &plusmn; 0.04)%, and (10.55 &plusmn; 1.80)%, and the background rejection power is about (6.21 &plusmn; 0.03) &times; 104, (9.03 &plusmn; 0.05) &times; 104, and (3.06 &plusmn; 0.32) &times; 104, respectively. This method gives a higher background rejection power in all energy ranges than the traditional morphological parameterization method and reaches comparable background rejection performance compared with supervised machine learning methods.

]]>Universe doi: 10.3390/universe8110568

Authors: Natalia Gorobey Alexander Lukyanenko Alexander V. Goltsev

A theory of the initial state of the universe is proposed within the framework of the Euclidean quantum theory of gravity. The theory is based on a quantum representation in which the action functional is implemented as an operator on the space of wave functionals depending on the 4D space metric and matter fields. The initial construction object is the eigenvalue of the action operator in the area of the origin of the universe with the given values of the 3D metric and matter fields on the boundary. The wave function of the initial state is plotted as an exponential of this eigenvalue, after a Wick rotation in the complex plane of the radial variable of the Euclidean 4D space. An estimate of the initial radius of the universe is proposed.

]]>Universe doi: 10.3390/universe8110569

Authors: Anna Uryson

We discuss the influence of extragalactic magnetic fields on the intensity of gamma-ray emission produced in electromagnetic cascades from ultra-high energy cosmic rays propagating in extragalactic space. Both cosmic rays and cascade particles propagate mostly out of galaxies, galactic clusters, and large-scale structures, as their relative volume is small. Therefore, their magnetic fields weakly affect emission produced in cascades. Yet, estimates of this influence can be useful in searching for dark matter particles when components of extragalactic gamma-ray background should be known, including cascade gamma-ray emission. To study magnetic field influence on cascade emission, we calculated cosmic particle propagation in fields of ~10&minus;6 and 10&minus;12 G (the former is typical inside galaxies and clusters and the latter is common in voids and outside galaxies and clusters). The calculated spectra of cascade gamma-ray emissions are similar in the range of ~107&ndash;109 eV, so analyzing cascade emission in this range it is not necessary to specify models of an extragalactic magnetic field.

]]>Universe doi: 10.3390/universe8110567

Authors: Vitalii Vertogradov Maxim Misyura

In this paper, we apply the gravitational decoupling method for dynamical systems in order to obtain a new type of solution that can describe a hairy dynamical black hole. We consider three cases of decoupling. The first one is the simplest and most well known when the mass function is the function only of space coordinate r. The second case is a Vaidya spacetime case when the mass function depends on time v. Finally, the third case represents the generalization of these two cases: the mass function is the function of both r and v. We also calculate the apparent horizon and singularity locations for all three cases.

]]>Universe doi: 10.3390/universe8110565

Authors: Yulia Shugay Vladimir Kalegaev Ksenia Kaportseva Vladimir Slemzin Denis Rodkin Valeriy Eremeev

Solar wind (SW) disturbances associated with coronal mass ejections (CMEs) cause significant geomagnetic storms, which may lead to the malfunction or damage of sensitive on-ground and space-based critical infrastructure. CMEs are formed in the solar corona, and then propagate to the Earth through the heliosphere as Interplanetary CME (ICME) structures. We describe the main principles in development with the online, semi-empirical system known as the Space Monitoring Data Center (SMDC) of the Moscow State University, which forecasts arrival of ICMEs to Earth. The initial parameters of CMEs (speeds, startup times, location of the source) are determined using data from publicly available catalogs based on solar images from space telescopes and coronagraphs. After selecting the events directed to Earth, the expected arrival time and speed of ICMEs at the L1 point are defined using the Drag-Based model (DBM), which describes propagation of CMEs through the heliosphere under interaction with the modeled quasi-stationary SW. We present the test results of the ICME forecast in the falling phase of Cycle 24 obtained with the basic version of SMDC in comparison with results of other models, its optimization and estimations of the confidence intervals, and probabilities of a successful forecast.

]]>Universe doi: 10.3390/universe8110566

Authors: Amit Kumar Rao Ankur Tripathi Bhupendra Chauhan Rudra Prakash Malik

In some of the physically interesting gauge systems, we show that the application of the Noether theorem does not lead to the deduction of the Becchi&ndash;Rouet&ndash;Stora&ndash;Tyutin (BRST) and anti-BRST charges that obey precisely the off-shell nilpotency property despite the fact that these charges are (i) derived by using the off-shell nilpotent (anti-)BRST symmetry transformations, (ii) found to be the generators of the above continuous symmetry transformations, and (iii) conserved with respect to the time-evolution due to the Euler&ndash;Lagrange equations of motion derived from the Lagrangians/Lagrangian densities (that describe the dynamics of these suitably chosen physical systems). We propose a systematic method for the derivation of the off-shell nilpotent (anti-)BRST charges from the corresponding non-nilpotent Noether (anti-)BRST charges. To corroborate the sanctity and preciseness of our proposal, we take into account the examples of (i) the one (0 + 1)-dimensional (1D) system of a massive spinning (i.e., SUSY) relativistic particle, (ii) the D-dimensional non-Abelian one-form gauge theory, and (iii) the Abelian two-form and the Stu&uml;ckelberg-modified version of the massive Abelian three-form gauge theories in any arbitrary D-dimension of spacetime. Our present endeavor is a brief review where some decisive proposals have been made and a few novel results have been obtained as far as the nilpotency property is concerned.

]]>Universe doi: 10.3390/universe8110564

Authors: Myungkuk Kim Youngman Kim Sangyong Jeon Chang-Hwan Lee

Total pion yields and &pi;&minus;/&pi;+ ratios in two Sn+Sn collision systems, 132Sn+124Sn (neutron rich) and 108Sn+112Sn (neutron poor) at E=270A MeV, are significant observables in SAMURAI Pion-Reconstruction and Ion-Tracker (S&pi;RIT) experiments. Based on a recently developed transport model, DaeJeon Boltzmann&ndash;Uehling&ndash;Uhlenbeck (DJBUU), we investigate the isospin-dependent inmedium effects by including density- and isospin-dependent cross sections for &Delta; baryon productions. We compare our results with the S&pi;RIT data by considering these effects. We find that the yields as well as the ratios strongly depend on the in-medium effect, especially isospin-dependent in-medium cross sections for &Delta; resonances.

]]>Universe doi: 10.3390/universe8110563

Authors: Mubashir Qayyum Efaza Ahmad Muhammad Bilal Riaz Jan Awrejcewicz

The main purpose of this research is to propose a new methodology to observe a class of time-fractional generalized fifth-order Korteweg&ndash;de Vries equations. Laplace transform along with a homotopy perturbation algorithm is utilized for the solution and analysis purpose in the current study. This extended technique provides improved and convergent series solutions through symbolic computation. The proposed methodology is applied to time-fractional Sawada&ndash;Kotera, Ito, Lax&rsquo;s, and Kaup&ndash;Kupershmidt models, which are induced from a generalized fifth-order KdV equation. For validity purposes, obtained and existing results at integral orders are compared. Convergence analysis was also performed by computing solutions and errors at different values in a fractional domain. Dynamic behavior of the fractional parameter is also studied graphically. Simulations affirm the dominance of the proposed algorithm in terms of accuracy and fewer computations as compared to other available schemes for fractional KdVs. Hence, the projected algorithm can be utilized for more advanced fractional models in physics and engineering.

]]>Universe doi: 10.3390/universe8110562

Authors: Kanaka Durga Reddybattula Likhita Sai Nelapudi Mefe Moses Venkata Ratnam Devanaboyina Masood Ashraf Ali Punyawi Jamjareegulgarn Sampad Kumar Panda

The forecasting of ionospheric electron density has been of great interest to the research scientists and engineers&rsquo; community as it significantly influences satellite-based navigation, positioning, and communication applications under the influence of space weather. Hence, the present paper adopts a long short-term memory (LSTM) deep learning network model to forecast the ionospheric total electron content (TEC) by exploiting global positioning system (GPS) observables, at a low latitude Indian location in Bangalore (IISC; Geographic 13.03&deg; N and 77.57&deg; E), during the 24th solar cycle. The proposed model uses about eight years of GPS-TEC data (from 2009 to 2017) for training and validation, whereas the data for 2018 was used for independent testing and forecasting of TEC. Apart from the input TEC parameters, the model considers sequential data of solar and geophysical indices to realize the effects. The performance of the model is evaluated by comparing the forecasted TEC values with the observed and global empirical ionosphere model (international reference ionosphere; IRI-2016) through a set of validation metrics. The analysis of the results during the test period showed that LSTM output closely followed the observed GPS-TEC data with a relatively minimal root mean square error (RMSE) of 1.6149 and the highest correlation coefficient (CC) of 0.992, as compared to IRI-2016. Furthermore, the day-to-day performance of LSTM was validated during the year 2018, inferring that the proposed model outcomes are significantly better than IRI-2016 at the considered location. Implementation of the model at other latitudinal locations of the region is suggested for an efficient regional forecast of TEC across the Indian region. The present work complements efforts towards establishing an efficient regional forecasting system for indices of ionospheric delays and irregularities, which are responsible for degrading static, as well as dynamic, space-based navigation system performances.

]]>Universe doi: 10.3390/universe8110561

Authors: Beatriz Villarroel Kristiaan Pelckmans Enrique Solano Mikael Laaksoharju Abel Souza Onyeuwaoma Nnaemeka Dom Khaoula Laggoune Jamal Mimouni Hichem Guergouri Lars Mattsson Aurora Lago García Johan Soodla Diego Castillo Matthew E. Shultz Rubby Aworka Sébastien Comerón Stefan Geier Geoffrey W. Marcy Alok C. Gupta Josefine Bergstedt Rudolf E. Bär Bart Buelens Emilio Enriquez Christopher K. Mellon Almudena Prieto Dismas Simiyu Wamalwa Rafael S. de Souza Martin J. Ward

The Vanishing &amp; Appearing Sources during a Century of Observations (VASCO) project investigates astronomical surveys spanning a time interval of 70 years, searching for unusual and exotic transients. We present herein the VASCO Citizen Science Project, which can identify unusual candidates driven by three different approaches: hypothesis, exploratory, and machine learning, which is particularly useful for SETI searches. To address the big data challenge, VASCO combines three methods: the Virtual Observatory, user-aided machine learning, and visual inspection through citizen science. Here we demonstrate the citizen science project and its improved candidate selection process, and we give a progress report. We also present the VASCO citizen science network led by amateur astronomy associations mainly located in Algeria, Cameroon, and Nigeria. At the moment of writing, the citizen science project has carefully examined 15,593 candidate image pairs in the data (ca. 10% of the candidates), and has so far identified 798 objects classified as &ldquo;vanished&rdquo;. The most interesting candidates will be followed up with optical and infrared imaging, together with the observations by the most potent radio telescopes.

]]>Universe doi: 10.3390/universe8110560

Authors: Qinyuan Zhang Xishui Tian Zhuo Li

IceCube measures a diffuse neutrino flux comparable to the Waxman-Bahcall bound, which suggests the possibility that the ultra-high energy cosmic rays (UHECRs) have a common origin with diffuse high energy neutrinos. We propose high energy gamma-ray and/or neutrino observations toward the arrival directions of UHECRs to search for the sources and test this possibility. We calculate the detection probability of gamma-ray/neutrino sources, and find that the average probability per UHECR of &gt;10 EeV is &sim;10% if the sensitivity of the gamma-ray or neutrino telescope is &sim;10&minus;12 erg cm&minus;2 s&minus;1 and the source number density is &sim;10&minus;5 Mpc&minus;3. Future gamma-ray and neutrino observations toward UHECRs, e.g., by LHAASO-WCDA, CTA, IceCube/Gen2, are encouraged to constrain the density of UHECR sources or even identify the sources of UHECRs.

]]>Universe doi: 10.3390/universe8110559

Authors: Ashraf Ayubinia Yongquan Xue Jong-Hak Woo Huynh Anh Nguyen Le Zhicheng He Halime Miraghaei Xiaozhi Lin

We investigate the ionized gas kinematics relationship with X-ray, radio and accreting properties using a sample of 348 nearby (z&lt;0.4) SDSS-FIRST-X-ray detected AGNs. X-ray properties of our sample are obtained from XMM-Newton, Swift and Chandra observations. We unveil the ionized gas outflows in our sample manifested by the non-gravitational broad component in [O iii]&lambda;5007&Aring; emission line profiles. From the comparison of the correlation of non-parametric outflow velocities (i.e., the velocity width, the maximal velocity of outflow and line dispersion) with X-ray luminosity and radio luminosity, we find that outflow velocities have similarly positive correlations with both X-ray and radio luminosity. After correcting for the gravitational component, we find that the [O iii] velocity dispersion normalized by stellar mass also increases with both X-ray luminosity and radio luminosity. We also find that, for a given X-ray (radio) luminosity, radio (X-ray) luminous AGNs have higher outflow velocities than non-radio (non-X-ray) luminous AGNs. Therefore, we find no clear preference between X-ray luminosity and radio luminosity in driving high-velocity ionized outflows and conclude that both AGN activity and small-scale jets contribute comparably. Moreover, there is no evidence that our obscured AGNs are preferentially associated with higher velocity outflows. Finally, we find a turning point around log(&lambda;Edd)&#8771;&minus;1.3 when we explore the dependency of outflow velocity on Eddington ratio. It can be interpreted considering the role of high radiation pressure (log(&lambda;Edd)&#8819;&minus;1.3) in causing drastic reduction in the covering factor of the circumnuclear materials.

]]>Universe doi: 10.3390/universe8110558

Authors: Yuri Stozhkov Vladimir Makhmutov Nikolay Svirzhevsky

Cosmic ray fluxes in the heliosphere are modulated by solar wind with an embedded solar interplanetary magnetic field. The solar activity changes with a period of ~11 year, and this is the main reason for the observed 11-year variations of cosmic ray fluxes. Besides this, the directions of magnetic fields in solar polar regions and in the heliosphere change to the opposite direction every ~11-years. This causes, in addition, the presence of another 22-year solar magnetic cycle and contributes features to the known ~11-cycle. In this article, we discuss the generally accepted picture of cosmic ray modulation in the heliosphere and show that it requires several changes.

]]>Universe doi: 10.3390/universe8110557

Authors: Alexander A. Khokhlachev Yuri I. Yermolaev Irina G. Lodkina Maria O. Riazantseva Liudmila S. Rakhmanova

Based on the OMNI database, the influence of the solar activity decrease in solar cycles (SCs) 23&ndash;24 on the behavior of the relative helium ions abundance N&alpha;/Np inside interplanetary coronal mass ejections (ICMEs) is investigated. The dependences of the helium abundance on the plasma and interplanetary magnetic field parameters in the epoch of high solar activity (SCs 21&ndash;22) and the epoch of low activity (SCs 23&ndash;24) are compared. It is shown that N&alpha;/Np significantly decreased in SCs 23&ndash;24 compared to SCs 21&ndash;22. The general trends of the dependences have not changed with the change of epoch, but the helium abundance dependences on some parameters (for example, the magnitude of the interplanetary magnetic field) have become weaker in the epoch of low activity than they were in the epoch of high activity. In addition, the dependence of the helium abundance on the distance from spacecraft to the ICME axis was revealed; the clearest dependence is observed in magnetic clouds. The N&alpha;/Np maximum is measured at the minimum distance, which confirms the hypothesis of the existence of a helium-enriched electric current inside an ICME.

]]>Universe doi: 10.3390/universe8110556

Authors: Giulia Maniccia Mariaveronica De Angelis Giovanni Montani

In this review, we analyse different aspects concerning the possibility to separate a gravity-matter system into a part which lives close to a quasi-classical state and a &ldquo;small&rdquo; quantum subset. The considered approaches are all relying on a WKB expansion of the dynamics by an order parameter and the natural arena consists of the Bianchi universe minisuperspace. We first discuss how, limiting the WKB expansion to the first order of approximation, it is possible to recover for the quantum subsystem a Schr&ouml;dinger equation, as written on the classical gravitational background. Then, after having tested the validity of the approximation scheme for the Bianchi I model, we give some applications for the quantum subsystem in the so-called &ldquo;corner&rdquo; configuration of the Bianchi IX model. We individualize the quantum variable in the small one of the two anisotropy degrees of freedom. The most surprising result is the possibility to obtain a non-singular Bianchi IX cosmology when the scenario is extrapolated backwards in time. In this respect, we provide some basic hints on the extension of this result to the generic cosmological solution. In the last part of the review, we consider the same scheme to the next order of approximation identifying the quantum subset as made of matter variables only. This way, we are considering the very fundamental problem of non-unitary morphology of the quantum gravity corrections to quantum field theory discussing some proposed reformulations. Instead of constructing the time dependence via that one of the classical gravitational variables on the label time as in previous works, we analyse a recent proposal to construct time by fixing a reference frame. This scheme can be reached both introducing the so-called &ldquo;kinematical action&rdquo;, as well as by the well-known Kuchar&ndash;Torre formulation. In both cases, the Schr&ouml;dinger equation, amended for quantum gravity corrections, has the same morphology and we provide a cosmological implementation of the model, to elucidate its possible predictions.

]]>Universe doi: 10.3390/universe8110555

Authors: Junlong Tian Xian Li Cheng Li

Collisions of very heavy nuclei 197Au+197Au at the energy range of 5&ndash;30 A MeV have been studied within the improved quantum molecular dynamics (ImQMD) model. A class of ternary events satisfying a nearly complete balance of mass numbers is selected and we find that the probability of ternary breakup depends on the incident energy and the impact parameter. It is also found that the largest probability of ternary breakup is located at the energy around 24 A MeV for the system 197Au+197Au. The experimental mass distributions and angular distributions for the system 197Au+197Au ternary breakup fragments can be reproduced well by the calculation with the ImQMD model at the energy of 15 A MeV. The modes and mechanisms of ternary and quaternary breakup are studied by time-dependent snapshots of ternary events. The direct prolate, direct oblate, and cascade ternary breakup modes, are manifested and their production probabilities are obtained. The characteristic features in ternary breakup events, three mass-comparable fragments, and the very fast, nearly collinear breakup, account for the two-preformed-neck shape of the composite system. The mean free path of nucleons in the reaction system is studied and the shorter mean free path is responsible for the ternary breakup with three mass comparable fragments, in which the two-body dissipation mechanism plays a dominant role.

]]>Universe doi: 10.3390/universe8110554

Authors: Stacey Alberts Allison Noble

Environment is one of the primary drivers of galaxy evolution; via multiple mechanisms, it can control the critical process of transforming galaxies from star forming to quiescent, commonly termed &ldquo;quenching&rdquo;. Despite its importance, however, we still do not have a clear view of how environmentally-driven quenching proceeds even in the most extreme environments: galaxy clusters and their progenitor proto-clusters. Recent advances in infrared capabilities have enabled transformative progress not only in the identification of these structures but in detailed analyses of quiescence, obscured star formation, and molecular gas in (proto-)cluster galaxies across cosmic time. In this review, we will discuss the current state of the literature regarding the quenching of galaxies in (proto-)clusters from the observational, infrared perspective. Our improved understanding of environmental galaxy evolution comes from unique observables across the distinct regimes of the near-, mid-, and far-infrared, crucial in the push to high redshift where massive galaxy growth is dominated by highly extinct, infrared-bright galaxies.

]]>Universe doi: 10.3390/universe8110553

Authors: Alexander Burinskii

We consider a consistent with gravity electron based on the overrotating Kerr-Newman (KH) solution and show that the earlier KH electron models proposed by Carter, Israel and L&oacute;pez in 1970&ndash;1990 should be modified by the Landau-Ginzburg theory, leading to a superconducting electron model consistent with gravity and quantum theory. Truncated by Israel and L&oacute;pez, the second sheet of the KN solution is rearranged and represented in a mirror form as a sheet of the positron, so that the modified KN system forms a quantum electron-positron vacuum interacting with gravity. Regularization of the KN black hole solution creates two new important effects leading to a strong gravitational interaction that acts on the Compton scale contrary to the usual Planck scale of Schwarzschild gravity: (A)&mdash;gravitational frame-dragging creates two Wilson loops acting at two boundaries of the modified KN solution, and (B)&mdash;formation of the flat superconducting core of the regularized KN solution creates a superconducting electron-positron vacuum state. The Landau-Ginzburg model shows that Wilson loops determine phases of two Higgs fields forming superconducting vacuum state of the modified KN solution, quantum vacuum of the electron-positron pairs. The phases of these Higgs fields correspond to two light-like modes of a classical relativistic ring string. We come to the conclusion that the electron models considered by Israel and L&oacute;pez are not complete and must be supplemented by a mirror structure that forms a quantum system consistent with QED.

]]>Universe doi: 10.3390/universe8110552

Authors: Kensuke Akita Masahide Yamaguchi

We review the distortions of spectra of relic neutrinos due to the interactions with electrons, positrons, and neutrinos in the early universe. We solve integro-differential kinetic equations for the neutrino density matrix, including vacuum three-flavor neutrino oscillations, oscillations in electron and positron background, a collision term and finite temperature corrections to electron mass and electromagnetic plasma up to the next-to-leading order O(e3). After that, we estimate the effects of the spectral distortions in neutrino decoupling on the number density and energy density of the Cosmic Neutrino Background (C&nu;B) in the current universe, and discuss the implications of these effects on the capture rates in direct detection of the C&nu;B on tritium, with emphasis on the PTOLEMY-type experiment. In addition, we find a precise value of the effective number of neutrinos, Neff=3.044. However, QED corrections to weak interaction rates at order O(e2GF2) and forward scattering of neutrinos via their self-interactions have not been precisely taken into account in the whole literature so far. Recent studies suggest that these neglections might induce uncertainties of &plusmn;(10&minus;3&ndash;10&minus;4) in Neff.

]]>Universe doi: 10.3390/universe8110551

Authors: Yao Cheng Liyun Zhang Qingfeng Pi Zhongzhong Zhu Xianming L. Han Prabhakar Misra Zilu Yang Baoda Li Linyan Jiang

Radio radiation has been detected across the Hertzsprung Russell diagram. We selected three objects with radio radiation (a semi-detached eclipsing binary V Crt, and two detached binaries WY Cnc and CG Cyg) that show magnetic activity. We made new photometric observations using a SARA 60 cm and NAOC 85 cm optical telescopes. Then, we obtained their orbital and starspot parameters by analyzing our light curves and published radial velocities using the updated Wilson-Devinney program. We revised the ephemeris information for V Crt and WY Cnc by analyzing the orbital minimum times. The orbital periods increased by 2.8 (&plusmn;2.1) &times;10&minus;9 d yr&minus;1 for V Crt, which maybe caused by mass transfer. The orbital periods decreased by &minus;8.641 (&plusmn;0.004) &times;10&minus;8 d yr&minus;1 for WY Cnc. Orbital period change for CG Cyg was also found and we used a third-body of M3 of 0.14 M&#8857; and a period of approximately 59.20 (0.36) yr to explain that. We also analysed the possible second period oscillation of CG Cyg with a cycle about 18.31 (0.06) yr. The long period changes of WY Cnc and CG Cyg might be caused by magnetic activity or stellar wind, rather than mass transfer.

]]>Universe doi: 10.3390/universe8110550

Authors: Arvind Mukundan Hsiang-Chen Wang

The vast universe, from its unfathomable ends to our very own Milky Way galaxy, is comprised of numerous celestial bodies&mdash;disparate yet each having their uniqueness. Amongst these bodies exist only a handful that have an environment that can nurture and sustain life. The Homo&nbsp;sapiens species has inhabited the planet, which is positioned in a precise way&mdash;Earth. It is an irrefutable truth that the planet Earth has provided us with all necessities for survival&mdash;for the human race to flourish and prosper and make scientific and technological advancements. Humans have always had an innate ardor for exploration&mdash;and now, since they have explored every nook and corner of this planet, inhabiting it and utilizing its resources, the time has come to alleviate the burden we have placed upon Earth to be the sole life-sustaining planet. With limited resources in our grasp and an ever-proliferating population, it is the need of the hour that we take a leap and go beyond the planet for inhabitation&mdash;explore the other celestial objects in our galaxy. Then, however, there arises a confounding conundrum&mdash;where do we go? The answer is right next to our home&mdash;the Red Planet, Mars. Space scientists have confirmed that Mars has conditions to support life and is the closest candidate for human inhabitation. The planet has certain similarities to Earth and its proximity provides us with convenient contact. This paper will be dealing with the conceptual design for the first city-state on Mars. Aggregating assumptions, research, and estimations, this first settlement project shall propose the most optimal means to explore, inhabit and colonize our sister planet, Mars.

]]>Universe doi: 10.3390/universe8100549

Authors: Javlon Rayimbaev Dilshodbek Bardiev Farrux Abdulxamidov Ahmadjon Abdujabbarov Bobomurat Ahmedov

In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes the shrinking of the outer horizon. We find that the range of the GB parameter &alpha;/M2&isin;(&minus;0.15869,1), and the extreme value of magnetic charge reaches up to gextr=0.886M, which allows for the existence of a BH horizon, while it is gextr=0.7698M for pure Bardeen BH. We also investigate the dynamics of magnetized particles around the magnetically charged Bardeen BH, assuming the particle&rsquo;s motion occurs in the equatorial plane in the proper observation frame, and the direction of the magnetic dipole moment of the particles is always kept radially and its magnitude is constant. Moreover, the dynamics of magnetically charged particles are also studied, and it is shown that both the energy and angular momentum of the particles corresponding to circular orbits increases with the increase of their magnetic charge. Finally, we also study collisions of magnetized, electrically neutral, and magnetically charged particles around the Bardeen BHs, where we provide analyses of critical angular momentum that may allow collision of the particles near-horizon radius, producing enormous values of center of mass energy of the collisions.

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