Universe doi: 10.3390/universe10040188

Authors: Anna Kraeva on behalf of the STAR Collaboration

The correlation femtoscopy technique makes it possible to estimate the geometric dimensions and lifetime of the particle emission region after the collision of ions. Measurements of the emission region characteristics not only at midrapidity but also at backward (forward) rapidity can provide new information about the source and make it possible to impose constraints on the heavy-ion collision models. This work is devoted to revealing the dependence of the spatial and temporal parameters of the emission region of identical pions in Au+Au collisions at sNN = 3 GeV from the fixed-target program of the STAR experiment. The extracted femtoscopic radii, Rout, Rside, Rlong, Rout&minus;long2, and the correlation strength, &lambda;, are presented as a function of collision centrality, pair rapidity, and transverse momentum. Physics implications will be discussed.

]]>Universe doi: 10.3390/universe10040187

Authors: Enrico Bozzo Lorenzo Amati Wayne Baumgartner Tzu-Ching Chang Bertrand Cordier Nicolas De Angelis Akihiro Doi Marco Feroci Cynthia Froning Jessica Gaskin Adam Goldstein Diego Götz Jon E. Grove Sylvain Guiriec Margarita Hernanz C. Michelle Hui Peter Jenke Daniel Kocevski Merlin Kole Chryssa Kouveliotou Thomas Maccarone Mark L. McConnell Hideo Matsuhara Paul O’Brien Nicolas Produit Paul S. Ray Peter Roming Andrea Santangelo Michael Seiffert Hui Sun Alexander van der Horst Peter Veres Jianyan Wei Nicholas White Colleen Wilson-Hodge Daisuke Yonetoku Weimin Yuan Shuang-Nan Zhang

Since their first discovery in the late 1960s, gamma-ray bursts have attracted an exponentially growing interest from the international community due to their central role in the most highly debated open questions of the modern research of astronomy, astrophysics, cosmology, and fundamental physics. These range from the intimate nuclear composition of high-density material within the core of ultra-dense neuron stars, to stellar evolution via the collapse of massive stars, the production and propagation of gravitational waves, as well as the exploration of the early universe by unveiling the first stars and galaxies (assessing also their evolution and cosmic re-ionization). GRBs in the past &sim;50 years have stimulated the development of cutting-edge technological instruments for observations of high-energy celestial sources from space, leading to the launch and successful operations of many different scientific missions (several of them still in data-taking mode currently). In this review, we provide a brief description of the GRB-dedicated missions from space being designed and developed for the future. The list of these projects, not meant to be exhaustive, shall serve as a reference to interested readers to understand what is likely to come next to lead the further development of GRB research and the associated phenomenology.

]]>Universe doi: 10.3390/universe10040186

Authors: Igor D. Volodin Maria O. Riazantseva Liudmila S. Rakhmanova Alexander A. Khokhlachev Yuri I. Yermolaev

This paper is devoted to the analysis of fluctuations in the solar wind plasma and interplanetary magnetic field parameters observed by Solar Orbiter and WIND spacecraft at different scales ranging from ~103 to 107 km. We consider two long data intervals where the distances between the spacecraft are 0.1 and 0.5 AU, respectively, and they are located close to the Sun&ndash;Earth line. Transformation of the fluctuation&rsquo;s properties on the way from the Sun to Earth is analyzed for different types of solar wind associated with quasi-stationary and transient solar phenomena. The time series of bulk speed are shown to undergo a slight modification, even for large spacecraft separation, while the time series of the interplanetary magnetic field magnitude and components as well as proton density may be transformed even at a relatively short distance. Though the large-scale solar wind structures propagate the distance up to 0.5 AU without significant change, local structures at smaller scales may be modified. The statistical properties of the fluctuations such as relative standard deviation or probability distribution function and its moments remain nearly unchanged at different distances between the two spacecraft and are likely to depend mostly on the type of the solar wind.

]]>Universe doi: 10.3390/universe10040185

Authors: Chunjian Liu Zhen Yao Yue Quan

In this paper, we investigate the mass accretion properties in the innermost regions of a viscously evolved protoplanetary disk and try to find some clues to the outburst events. In our newly developed one-dimensional time-dependent disk model based on the diffusion equation for surface density, we take into account the following physical effects: the gravitational collapse of the parent molecular cloud core, the irradiation from the central star to the disk, the effect of the photoevaporation mechanism, the viscosity due to the magnetorotational instability (MRI) and the gravitational instability (GI), and the thermal ionization mechanism in the inner regions. We find that the mass accretion rate M&middot;disk in the innermost regions is statistically high enough to generate outbursts, although there are regions where the accretion rate is low. Additionally, we find that there is a weak correlation between the high mass accretion rate M&middot;disk and the molecular cloud core&rsquo;s properties (angular velocity &omega; and mass Mcd), as well as a strong correlation with the minimum viscosity parameter &alpha;min. In general, there are two regions of outburst, the inner Region I and outer Region II. The outburst of Region I is caused by the MRI mechanism and thermal instability, while neither the MRI, the GI, nor the thermal instability causes the outburst of Region II. Our analysis suggests that the outer Region II is dominated by, or largely related to, the Rosseland mean opacity &kappa;R and the &alpha;min parameter.

]]>Universe doi: 10.3390/universe10040184

Authors: Eleonora Di Valentino Leandros Perivolaropoulos Jackson Levi Said

The standard cosmological model, known as &Lambda;CDM, has been remarkably successful in providing a coherent and predictive framework for understanding the Universe&rsquo;s evolution, its large-scale structure, and cosmic microwave background (CMB) radiation [...]

]]>Universe doi: 10.3390/universe10040183

Authors: Nektarios Vlahakis

A minimalist approach to the linear stability problem in fluid dynamics is developed that ensures efficiency by utilizing only the essential elements required to find the eigenvalues for given boundary conditions. It is shown that the problem is equivalent to a single first-order ordinary differential equation, and that studying the argument of the unknown complex function in the eigenvalue space is sufficient to find the dispersion relation. The method is applied to a model for relativistic magnetized astrophysical jets.

]]>Universe doi: 10.3390/universe10040182

Authors: Yanke Tang Xiaolu Li Kai Xiao Ning Gai Shijie Li Futong Dong Yifan Wang Yang Gao

In recent years, the rapid development of exoplanet research has provided us with an opportunity to better understand planetary systems in the universe and to search for signs of life. In order to further investigate the prevalence of habitable exoplanets and to validate planetary formation theories, as well as to comprehend planetary evolution, we have utilized confirmed exoplanet data obtained from the NASA Exoplanet Archive database, including data released by telescopes such as Kepler and TESS. By analyzing these data, we have selected a sample of planets around F, G, K, and M-type stars within a radius range of 1 to 20 R&oplus; and with orbital periods ranging from 0.4 days to 400 days. Using the IDEM method based on these data, we calculated the overall formation rate, which is estimated to be 2.02%. Then, we use these data to analyze the relationship among planet formation rates, stellar metallicity, and stellar gravitational acceleration (logg). We firstly find that the formation rate of giant planets is higher around metal-rich stellars, but it inhibits the formation of gas giants when logg &gt; 4.5, yet the stellar metallicity seems to have no effect on the formation rate of smaller planets. Secondly, the host stellar gravitational acceleration affects the relationship between planet formation rate and orbital period. Thirdly, there is a robust power-law relationship between the orbital period of smaller planets and their formation rate. Finally, we find that, for a given orbital period, there is a positive correlation between the planet formation rate and the logg.

]]>Universe doi: 10.3390/universe10040181

Authors: Eugenio Bianchi Pierre Martin-Dussaud

The metric field of general relativity is almost fully determined by its causal structure. Yet, in spin foam models of quantum gravity, the role played by the causal structure is still largely unexplored. The goal of this paper is to clarify how causality is encoded in such models. The quest unveils the physical meaning of the orientation of the two-complex and its role as a dynamical variable. We propose a causal version of the EPRL spin foam model and discuss the role of the causal structure in the reconstruction of a semiclassical space&ndash;time geometry.

]]>Universe doi: 10.3390/universe10040180

Authors: Georgy I. Burde

&lsquo;Small-scale cosmology&rsquo; is a theory designed to incorporate the linear redshift versus distance relation, which is inferred from observations, into the theoretical framework independent of the global Robertson&ndash;Walker&ndash;Friedman (RWF)-type models. The motivation behind this is that the RWF cosmological models, based on the assumptions of homogeneity and a constant matter density, as well as the concept of expanding space inherent to them are not applicable on the scales of observations from which the linear Hubble law is inferred. Therefore, explaining the Hubble law as the small redshift limit of the RWF model or as an effect of expanding space is inconsistent. Thus, the Hubble linear relation between the redshift of an extragalactic object and its distance should be considered an independent law of nature valid in the range of the distances where the RWF cosmology is not valid. In general, the theory, based on that concept, can be developed in different ways. In the present paper, &lsquo;small-scale cosmology&rsquo; is formulated as a theory operating in the (redshift&ndash;object coordinates) space, which allows developing a conceptual and computational basis of the theory along the lines of that of special relativity. In such a theory, the condition of invariance of the Hubble law with respect to a change in the observer acceleration plays a central role. In pursuing this approach, the effectiveness of group theoretical methods is exploited. Applying the Lie group method yields transformations of the variables (the redshift and space coordinates of a cosmological object) between the reference frames of the accelerated observers. In this paper, the transformations are applied to studying the effects of the solar system observer acceleration on the observed shape, distribution and rotation curves of galaxy clusters.

]]>Universe doi: 10.3390/universe10040179

Authors: Ramón Serrano Montesinos Juan Antonio Morales-Lladosa

Our starting point is the covariant coordinate transformation equation of a relativistic positioning system in Minkowski space&ndash;time that maps the receiver&rsquo;s emission coordinates (proper times broadcast by the emitters) to its coordinates in some inertial reference frame. Bancroft&rsquo;s analytical (closed-form) solution to the basic pseudorange navigation equations with four emitters is recovered, and the subjacent elements are geometrically interpreted. The case of four static beacons is analysed as a clarifying situation.

]]>Universe doi: 10.3390/universe10040178

Authors: Ioannis Contopoulos Ioannis Dimitropoulos Dimitris Ntotsikas Konstantinos N. Gourgouliatos

We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has never been obtained before is that all current time-dependent simulations are initialized with a vacuum dipole configuration that extends to infinity; thus, their final steady-state solution also extends to infinity. Under special conditions, such a confined configuration may be attained when the neutron star first forms in the interior of a collapsing star during a supernova explosion, or when it accretes from an external wind or disk from a donor star. It is shown that this new maximally closed non-decelerating solution is the limit of a continuous sequence of standard magnetospheres with open and closed field lines when the amount of open field lines gradually drops to zero. The minimum energy solution in this sequence is a standard magnetosphere in which the closed field line region extends up to about 80% of the light cylinder. We estimate that the released energy when the new solution transitions to the minimum energy one is enough to power a fast radio burst.

]]>Universe doi: 10.3390/universe10040177

Authors: Jiayi Xia Yen Chin Ong

Both classical and quantum arguments suggest that if Barrow entropy is correct, its index &delta; must be energy-dependent, which would affect the very early universe. Based on thermodynamic stability that sufficiently large black holes should not fragment, we argue that Barrow entropy correction must be small, except possibly at the Planckian regime. Furthermore, the fact that a solar mass black hole does not fragment implies an upper bound &delta;&#8818;O(10&minus;3), which surprisingly lies in the same range as the bound obtained from some cosmological considerations assuming fixed &delta;. This indicates that allowing &delta; to run does not raise its allowed value. We briefly comment on the case of Kaniadakis entropy.

]]>Universe doi: 10.3390/universe10040176

Authors: Imtiaz Khan Waqas Ahmed Tianjun Li Shabbar Raza

Because there are a few typos in the supersymmetry-breaking sfermion masses and trilinear soft term, regarding the current Large Hadron Collider (LHC) and dark matter searches, we revisit a three-family Pati&ndash;Salam model based on intersecting D6-branes in Type IIA string theory on a T6/(Z2&times;Z2) orientifold with a realistic phenomenology. We study the viable parameter space and discuss the spectrum consistent with the current LHC Supersymmetry searches and the dark matter relic density bounds from the Planck 2018 data. For the gluinos and first two generations of sfermions, we observe that the gluino mass is in the range [2, 14] TeV, the squarks mass range is [2, 13] TeV and the sleptons mass is in the range [1, 5] TeV. We achieve the cold dark matter relic density consistent with 5&sigma; Planck 2018 bounds via A-funnel and coannihilation channels such as stop&ndash;neutralino, stau&ndash;neutralino, and chargino&ndash;neutralino. Except for a few chargino&ndash;neutralino coannihilation solutions, these solutions satisfy current nucleon-neutralino spin-independent and spin-dependent scattering cross-sections and may be probed by future dark matter searches.

]]>Universe doi: 10.3390/universe10040175

Authors: Xu Zhu Hui Liu Xinji Wu Rushuang Zhao Qijun Zhi Shijun Dang Lunhua Shang Shuo Xiao Hongwei Xu Weilan Li Ruwen Tian Shidong Wang Zefeng Tu

Using the rotating vector model (RVM) and aiming to constrain the value of the magnetic inclination angle (&alpha;), we perform a least-squares fit on the linearly polarized position angles of 125 pulsars from Parkes 64 m archive data at 1400 MHz. Subsequently, a statistical analysis of the normalized Q parameters is carried out. Furthermore, based on the Q-parameter, we provide a further understanding of the geometry of the radio emission region of the pulsar. In this statistical sample, about 1/5 of the sample is clustered at 0, suggesting that this part of the pulsar is viewed from the center of the radiation cone. For the rest of the pulsars, the Q parameters follow a uniform distribution, supporting the conclusion that the interface of the radiation cone is non-elliptical.

]]>Universe doi: 10.3390/universe10040173

Authors: Cheuk-Yin Wong

The Schwinger confinement mechanism stipulates that a massless fermion and a massless antifermion are confined as a massive boson when they interact in the Abelian QED interaction in (1+1)D.If we approximate light quarks as massless and apply the Schwinger confinement mechanism to quarks, we can infer that a light quark and a light antiquark interacting in the Abelian QED interaction are confined as a QED meson in (1+1)D. Similarly, a light quark and a light antiquark interacting in the QCD interaction in the quasi-Abelian approximation will be confined as a QCD meson in (1+1)D. The QED and QCD mesons in (1+1)D can represent physical mesons in (3+1)D when the flux tube radius is properly taken into account. Such a theory leads to a reasonable description of the masses of &pi;0,&eta;, and &eta;&prime;, and its extrapolation to the unknown QED sector yields an isoscalar QED meson at about 17 MeV and an isovector QED meson at about 38 MeV. The observations of the anomalous soft photons, the hypothetical X17 particle, and the hypothetical E38 particle bear promising evidence for the possible existence of the QED mesons. Pending further confirmation, they hold important implications on the properties on the quarks and their interactions.

]]>Universe doi: 10.3390/universe10040174

Authors: Shijie Zheng Dawei Han Heng Xu Kejia Lee Jianping Yuan Haoxi Wang Mingyu Ge Liang Zhang Yongye Li Yitao Yin Xiang Ma Yong Chen Shuangnan Zhang

Millisecond pulsars (MSPs) are known for their long-term stability. Using six years of observations from the Neutron Star Interior Composition Explorer (NICER), we have conducted an in-depth analysis of the X-ray timing results for six MSPs: PSRs B1937+21, B1821-24, J0437-4715, J0030+0451, J0218+4232, and J2124-3358. The timing stability parameter &sigma;z has been calculated, revealing remarkable timing precision on the order of 10&minus;14 for PSRs B1937+21 and J0437-4715, and 10&minus;13 for PSRs B1821-24, J0218+4232, and J0030+0451 over a timescale of 1000 days. These findings underscore the feasibility of autonomous in-orbit timekeeping using X-ray observations of MSPs. In addition, the consistency of long-term spin-down noise in the X-ray and radio bands has been investigated by comparison with IPTA radio data.

]]>Universe doi: 10.3390/universe10040172

Authors: Tekin Dereli Philippe Nounahon Todor Popov

The Landau problem and harmonic oscillator in the plane share a Hilbert space that carries the structure of Dirac&rsquo;s remarkable so(2,3) representation. We show that the orthosymplectic algebra osp(1|4) is the spectrum generating algebra for the Landau problem and, hence, for the 2D isotropic harmonic oscillator. The 2D harmonic oscillator is in duality with the 2D quantum Coulomb&ndash;Kepler systems, with the osp(1|4) symmetry broken down to the conformal symmetry so(2,3). The even so(2,3) submodule (coined Rac) generated from the ground state of zero angular momentum is identified with the Hilbert space of a 2D hydrogen atom. An odd element of the superalgebra osp(1|4) creates a pseudo-vacuum with intrinsic angular momentum 1/2 from the vacuum. The odd so(2,3)-submodule (coined Di) built upon the pseudo-vacuum is the Hilbert space of a magnetized 2D hydrogen atom: a quantum system of a dyon and an electron. Thus, the Hilbert space of the Landau problem is a direct sum of two massless unitary so(2,3) representations, namely, the Di and Rac singletons introduced by Flato and Fronsdal.

]]>Universe doi: 10.3390/universe10040171

Authors: Xiao-Bo Zou Soumya D. Mohanty Hong-Gang Luo Yu-Xiao Liu

Extreme-mass-ratio inspirals (EMRIs) are significant observational targets for spaceborne gravitational wave detectors, namely, LISA, Taiji, and Tianqin, which involve the inspiral of stellar-mass compact objects into massive black holes (MBHs) with a mass range of approximately 104&sim;107M&#8857;. EMRIs are estimated to produce long-lived gravitational wave signals with more than 105 cycles before plunge, making them an ideal laboratory for exploring the strong-gravity properties of the spacetimes around the MBHs, stellar dynamics in galactic nuclei, and properties of the MBHs itself. However, the complexity of the waveform model, which involves the superposition of multiple harmonics, as well as the high-dimensional and large-volume parameter space, make the fully coherent search challenging. In our previous work, we proposed a 10-dimensional search using Particle Swarm Optimization (PSO) with local maximization over the three initial angles. In this study, we extend the search to an 8-dimensional PSO with local maximization over both the three initial angles and the angles of spin direction of the MBH, where the latter contribute a time-independent amplitude to the waveforms. Additionally, we propose a 7-dimensional PSO search by using a fiducial value for the initial orbital frequency and shifting the corresponding 8-dimensional Time Delay Interferometry responses until a certain lag returns the corresponding 8-dimensional log-likelihood ratio&rsquo;s maximum. The reduced dimensionality likelihoods enable us to successfully search for EMRI signals with a duration of 0.5 years and signal-to-noise ratio of 50 within a wider search range than our previous study. However, the ranges used by both the LISA Data Challenge (LDC) and Mock LISA Data Challenge (MLDC) to generate their simulated signals are still wider than the those we currently employ in our direct searches. Consequently, we discuss further developments, such as using a hierarchical search to narrow down the search ranges of certain parameters and applying Graphics Processing Units to speed up the code. These advances aim to improve the efficiency, accuracy, and generality of the EMRI search algorithm.

]]>Universe doi: 10.3390/universe10040170

Authors: Antonio Capolupo Giuseppe De Maria Simone Monda Aniello Quaranta Raoul Serao

In the framework of quantum field theory, we analyze the neutrino oscillations in the presence of a torsion background. We consider the Einstein&ndash;Cartan theory and we study the cases of constant torsion and of linearly time-dependent torsion. We derive new neutrino oscillation formulae which depend on the spin orientation. Indeed, the energy splitting induced by the torsion influences oscillation amplitudes and frequencies. This effect is maximal for values of torsion of the same order of the neutrino masses and for very low momenta, and disappears for large values of torsion. Moreover, neutrino oscillation is inhibited for intensities of torsion term much larger than neutrino masses and momentum. The modifications induced by torsion on the CP-asymmetry are also presented. Future experiments, such as PTOLEMY, which have as a goal the analysis of the cosmological background of neutrino (which have very low momenta), can provide insights into the effect shown here.

]]>Universe doi: 10.3390/universe10040169

Authors: Alexandre V. Ivanchik Oleg A. Kurichin Vlad Yu. Yurchenko

At least two relics of the Big Bang have survived: the cosmological microwave background (CMB) and the cosmological neutrino background (C&nu;B). Being the second most abundant particle in the universe, the neutrino has a significant impact on its evolution from the Big Bang to the present day. Neutrinos affect the following cosmological processes: the expansion rate of the universe, its chemical and isotopic composition, the CMB anisotropy and the formation of the large-scale structure of the universe. Another relic neutrino background is theoretically predicted, it consists of non-equilibrium antineutrinos of Primordial Nucleosynthesis arising as a result of the decay of neutrons and tritium nuclei. Such antineutrinos are an indicator of the baryon asymmetry of the universe. In addition to experimentally detectable active neutrinos, the existence of sterile neutrinos is theoretically predicted to generate neutrino masses and explain their oscillations. Sterile neutrinos can also solve such cosmological problems as the baryonic asymmetry of the universe and the nature of dark matter. The recent results of several independent experiments point to the possibility of the existence of a light sterile neutrino. However, the existence of such a neutrino is inconsistent with the predictions of the Standard Cosmological Model. The inclusion of a non-zero lepton asymmetry of the universe and/or increasing the energy density of active neutrinos can eliminate these contradictions and reconcile the possible existence of sterile neutrinos with Primordial Nucleosynthesis, the CMB anisotropy, and also reduce the H0-tension. In this brief review, we discuss the influence of the physical properties of active and sterile neutrinos on the evolution of the universe from the Big Bang to the present day.

]]>Universe doi: 10.3390/universe10040168

Authors: Tran The Anh Tran Dinh Trong Attila J. Krasznahorkay Attila Krasznahorkay József Molnár Zoltán Pintye Nguyen Ai Viet Nguyen The Nghia Do Thi Khanh Linh Bui Thi Hoa Le Xuan Chung Nguyen Tuan Anh

We have repeated the experiment performed recently by ATOMKI Laboratory (Debrecen, Hungary), which may indicate a new particle called X17 in the literature. In order to obtain a reliable and independent result, we used a different structure of the electron&ndash;positron pair spectrometer at the VNU University of Science. The spectrometer has two arms and simpler acceptance and efficiency as a function of the correlation angle, but the other conditions of the experiment were very similar to the published ones. We could confirm the presence of the anomaly measured at Ep = 1225 keV, which is above the Ep = 1040 keV resonance.

]]>Universe doi: 10.3390/universe10040167

Authors: Luca Nanni

The Standard Model is an up-to-date theory that best summarizes current knowledge in particle physics. Although some problems still remain open, it represents the leading model which all physicists refer to. One of the pillars which underpin the Standard Model is represented by the Lorentz invariance of the equations that form its backbone. These equations made it possible to predict the existence of particles and phenomena that experimental physics had not yet been able to detect. The first hint of formulating a fundamental theory of particles can be found in the 1932 Majorana equation, formulated when electrons and protons were the only known particles. Today we know that parts of the hypotheses set by Majorana were not correct, but his equation hid concepts that are found in the Standard Model. In this study, the Majorana equation is revisited and solved for free particles. The time-like, light-like and space-like solutions, represented by infinite-component wave functions, are discussed.

]]>Universe doi: 10.3390/universe10040166

Authors: Arkady A. Popov Sergey G. Rubin Alexander S. Sakharov

The origin and evolution of supermassive black holes (SMBHs) in our universe have sparked controversy. In this study, we explore the hypothesis that some of these black holes may have seeded from the direct collapse of dark energy domains with density significantly higher than the surrounding regions. The mechanism of the origin of such domains relies on the inflationary evolution of a scalar field acting in D dimensions, which is associated with the cosmological constant in our four-dimensional spacetime manifold. Inner space quantum fluctuations of the field during inflation are responsible for the spatial variations of the dark energy density in our space. This finding holds particular significance, especially considering recent evidence from pulsar timing array observations, which supports the existence of a stochastic gravitational wave background consisting of SMBH mergers.

]]>Universe doi: 10.3390/universe10040165

Authors: Vladimir N. Yershov

The main feature of elliptical space&mdash;the topological identification of its antipodal points&mdash;could be fundamental for understanding the nature of the cosmological redshift. The physical interpretation of the mathematical (topological) structure of elliptical space is made by using physical connections in the form of Einstein-Rosen bridges (also called &ldquo;wormholes&rdquo;). The Schwarzschild metric of these structures embedded into a dynamic (expanding) spacetime corresponds to McVittie&rsquo;s solution of Einstein&rsquo;s field equations. The cosmological redshift of spectral lines of remote sources in this metric is a combination of gravitational redshift and the time-dependent scale factor of the Friedmann-Lemaitre-Robertson-Walker metric. I compare calculated distance moduli of type-Ia supernovae, which are commonly regarded as &ldquo;standard candles&rdquo; in cosmology, with the observational data published in the catalogue &ldquo;Pantheon+&rdquo;. The constraint based on these accurate data gives a much smaller expansion rate of the Universe than is currently assumed by modern cosmology, the major part of the cosmological redshift being gravitational by its nature. The estimated age of the Universe within the discussed model is 1.48&middot;1012 yr, which is more than two orders of magnitude larger than the age assumed by using the standard cosmological model parameters.

]]>Universe doi: 10.3390/universe10040164

Authors: Alessandro Granelli

This review provides a succinct overview of the basic aspects of neutrino physics. The topics covered include neutrinos in the standard model and the three-neutrino mixing scheme; the current status of neutrino oscillation measurements and what remains to be determined; the seesaw mechanisms for neutrino mass generation and the associated phenomenology, including the leptogenesis mechanism to explain the observed matter&ndash;antimatter asymmetry of the Universe; and models for the origin of the pattern of neutrino mixing and lepton masses based on discrete flavour symmetries and modular invariance.

]]>Universe doi: 10.3390/universe10040163

Authors: Alessandro Carosi Alicia López-Oramas

The development of the latest generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) over recent decades has led to the discovery of new extreme astrophysical phenomena in the very-high-energy (VHE, E &gt; 100 GeV) gamma-ray regime. Time-domain and multi-messenger astronomy are inevitably connected to the physics of transient VHE emitters, which show unexpected (and mostly unpredictable) flaring or exploding episodes at different timescales. These transients often share the physical processes responsible for the production of the gamma-ray emission, through cosmic-ray acceleration, magnetic reconnection, jet production and/or outflows, and shocks interactions. In this review, we present an up-to-date overview of the VHE transients field, spanning from novae to supernovae, neutrino counterparts or fast radio bursts, among others, and we outline the expectations for future facilities.

]]>Universe doi: 10.3390/universe10040162

Authors: Francisco S. N. Lobo José Pedro Mimoso Jessica Santiago Matt Visser

Redshift drift is the phenomenon whereby the observed redshift between an emitter and observer comoving with the Hubble flow in an expanding FLRW universe will slowly evolve&mdash;on a timescale comparable to the Hubble time. In a previous article, three of the current authors performed a cosmographic analysis of the redshift drift in an FLRW universe, temporarily putting aside the issue of dynamics (the Friedmann equations). In the current article, we add dynamics while still remaining within the framework of an exact FLRW universe. We developed a suitable generic matter model and applied it to both standard FLRW and various dark energy models. Furthermore, we present an analysis of the utility of alternative cosmographic variables to describe the redshift drift data.

]]>Universe doi: 10.3390/universe10040161

Authors: L. P. Csernai T. Csörgő I. Papp K. Tamosiunas M. Csete A. Szenes D. Vass T. S. Biró N. Kroó

Hanbury-Brown and Twiss analysis is used to determine the size and timespan of emitted particles. Here, we propose to adapt this method for laser-induced nanoplasmonic inertial confinement fusion to determine the parameters of emitted Deuterium and Helium4 nuclei. This communication is a short article that presents part of a larger study over multiple years. It presents a cutting edge method that is new in the field of Inertial Confinement Fusion.

]]>Universe doi: 10.3390/universe10040160

Authors: Huanchen Hu Paulo C. C. Freire

Neutron stars (NSs) are compact objects that host the densest forms of matter in the observable universe, providing unique opportunities to study the behaviour of matter at extreme densities. While precision measurements of NS masses through pulsar timing have imposed effective constraints on the equation of state (EoS) of dense matter, accurately determining the radius or moment of inertia (MoI) of an NS remains a major challenge. This article presents a detailed review on measuring the Lense&ndash;Thirring (LT) precession effect in the orbit of binary pulsars, which would give access to the MoI of NSs and offer further constraints on the EoS. We discuss the suitability of certain classes of binary pulsars for measuring the LT precession from the perspective of binary star evolution and highlight five pulsars that exhibit properties promising to realise these goals in the near future. Finally, discoveries of compact binaries with shorter orbital periods hold the potential to greatly enhance measurements of the MoI of NSs. The MoI measurements of binary pulsars are pivotal to advancing our understanding of matter at supranuclear densities, as well as improving the precision of gravity tests, such as the orbital decay due to gravitational wave emission, and of tests of alternative gravity theories.

]]>Universe doi: 10.3390/universe10040159

Authors: Sebastian Schuster Matt Visser

Analogue space-times (and in particular metamaterial analogue space-times) have a long varied and rather complex history. Much of the previous related work to this field has focused on spherically symmetric models; however, axial symmetry is much more relevant for mimicking astrophysically interesting systems that are typically subject to rotation. Now it is well known that physically reasonable stationary axisymmetric space-times can, under very mild technical conditions, be put into Boyer&ndash;Lindquist form. Unfortunately, a metric presented in Boyer&ndash;Lindquist form is not well adapted to the &ldquo;quasi-Cartesian&rdquo; metamaterial analysis that we developed in our previous articles on &ldquo;bespoke analogue space-times&rdquo;. In the current article, we shall first focus specifically on various space-time metrics presented in Boyer&ndash;Lindquist form, and subsequently determine a suitable set of equivalent metamaterial susceptibility tensors in a laboratory setting. We shall then turn to analyzing generic space-times, not even necessarily stationary, again determining a suitable set of equivalent metamaterial susceptibility tensors. Perhaps surprisingly, we find that the well-known ADM formalism proves to be not particularly useful, and that it is instead the dual &ldquo;threaded&rdquo; (Kaluza&ndash;Klein&ndash;inspired) formalism that provides much more tractable results. While the background laboratory metric is (for mathematical simplicity and physical plausibility) always taken to be Riemann flat, we will allow for arbitrary curvilinear coordinate systems on the flat background space-time. Finally, for completeness, we shall reconsider spherically symmetric space-times, but now in general spherical polar coordinates rather than quasi-Cartesian coordinates. In summary, this article provides a set of general-purpose calculational tools that can readily be adapted for mimicking various interesting (curved) space-times by using nontrivial susceptibility tensors in general (background-flat) laboratory settings.

]]>Universe doi: 10.3390/universe10040158

Authors: Kaustubh Rajwade Joeri van Leeuwen

Ephemeral Fast Radio Bursts (FRBs) must be powered by some of the most energetic processes in the Universe. That makes them highly interesting in their own right, and as precise probes for estimating cosmological parameters. This field thus poses a unique challenge: FRBs must be detected promptly and immediately localised and studied based only on that single millisecond-duration flash. The problem is that the burst occurrence is highly unpredictable and that their distance strongly suppresses their brightness. Since the discovery of FRBs in single-dish archival data in 2007, detection software has evolved tremendously. Pipelines now detect bursts in real time within a matter of seconds, operate on interferometers, buffer high-time and frequency resolution data, and issue real-time alerts to other observatories for rapid multi-wavelength follow-up. In this paper, we review the components that comprise a FRB search software pipeline, we discuss the proven techniques that were adopted from pulsar searches, we highlight newer, more efficient techniques for detecting FRBs, and we conclude by discussing the proposed novel future methodologies that may power the search for FRBs in the era of big data astronomy.

]]>Universe doi: 10.3390/universe10040157

Authors: Hong-Bo Li Yong Gao Lijing Shao Ren-Xin Xu

Compact stars have been perceived as natural laboratories of matter at an extremely high density. The uncertainties of the equation of state (EOS) of matter can be constrained by observing compact stars. In this review, we investigate the EOSs, global structure, and elastic properties of compact stars. We focus in detail on how to constrain the above properties of compact stars via asteroseismology. Observations that include studies of quasi-periodic oscillations from giant flares of soft gamma-ray repeaters and gravitational waves provide information about the elastic properties and internal compositions of compact stars.

]]>Universe doi: 10.3390/universe10040156

Authors: Luigi Foschini Benedetta Dalla Barba Merja Tornikoski Heinz Andernach Paola Marziani Alan P. Marscher Svetlana G. Jorstad Emilia Järvelä Sonia Antón Elena Dalla Bontà

We present the results of a comparison between different methods to estimate the power of relativistic jets from active galactic nuclei (AGN). We selected a sample of 32 objects (21 flat-spectrum radio quasars, 7 BL Lacertae objects, 2 misaligned AGN, and 2 changing-look AGN) from the very large baseline array (VLBA) observations at 43 GHz of the Boston University blazar program. We then calculated the total, radiative, and kinetic jet power from both radio and high-energy gamma-ray observations, and compared the values. We found an excellent agreement between the radiative power calculated by using the Blandford and K&ouml;nigl model with 37 or 43 GHz data and the values derived from the high-energy &gamma;-ray luminosity. The agreement is still acceptable if 15 GHz data are used, although with a larger dispersion, but it improves if we use a constant fraction of the &gamma;-ray luminosity. We found a good agreement also for the kinetic power calculated with the Blandford and K&ouml;nigl model with 15 GHz data and the value from the extended radio emission. We also propose some easy-to-use equations to estimate the jet power.

]]>Universe doi: 10.3390/universe10040155

Authors: Svyatoslav Dedikov Evgenii Vasiliev

The destructionof clouds by strong shocks and hot winds is the key process responsible for the transporting of metals and dust from the ISM to the ICM/IGM, and establishing the multiphase structure in and around galaxies. In this work, we perform a detailed analysis of this process using two different approaches for tracking the cloud material (gas and dust): the so-called &lsquo;colored&rsquo; fluid, and the Lagrangian (trace) particles. We find that for the clouds in the hot phase (T&gt;105 K), the two methods produce significantly different mass fractions and velocities of the cloud material. In contrast, the two methods produce similar results for the clouds that are in the warm/cold phases (T&lt;105 K). We find that the Kelvin&ndash;Helmholtz instability is suppressed in the warm clouds of size &sim;100 pc and metallicity Z&gt; 0.1Zduetoeffectivegascooling.ThiscausesadelayinthedestructionofsuchcloudsthatareinteractingwiththehotICMflow.Wedemonstratethatthedustparticlesthatareevacuatedfromtheir&lsquo;parent&rsquo;cloudstothehotmediumshowdifferentdynamicswhencomparedtothatoftheLagrangian(trace)particles.Ourresultsindicatethatthedustgrainssweptouttothehotgasaredestroyed.

]]>Universe doi: 10.3390/universe10040154

Authors: M. A. Mahmoud Somaia Hamdi A. Radi M. A. El-Borie E. A. Tayel

The present work presents a study of jet production in the central region (|&eta;| &lt; 2.5) and the forward region (3 &lt; |&eta;| &lt; 5) in proton&ndash;proton collisions at different energies: s = 13.6 TeV, s = 20 TeV, and s = 27 TeV. These energies are the present and expected future energies of the Large Hadron Collider. In addition, the measurement of dijets&mdash;where the dijet selected is the one leading the jet in the central region and the second jet is the one with the sub-leading role in the forward region&mdash;was investigated with the same collision energies. Jets are reconstructed with the anti-kT (R = 0.5) algorithm in the transverse momentum range pT = 15&ndash;1000 GeV/c. Different Monte Carlo event generators were used: PYTHIA, HERWIG, and EPOS-LHC. The momentum, multiplicity, energy, pseudorapidity, and azimuthal angle of the jets were measured. In addition, the dijet multiplicity and the difference in the azimuthal angle were measured. The generation of events was carried out using the Rivet analysis framework. It is observed that, when the energy of the collision increases, the production of the jets in the central and forward regions and the dijets multiplicity increase; overall an agreement is observed between the three event generators. The disagreement between the different generators points to potential areas for development or additional study.

]]>Universe doi: 10.3390/universe10040153

Authors: Stefano Vercellone Carlotta Pittori Marco Tavani

The &gamma;-ray sky above a few tens of megaelectronvolts (MeV) reveals some of the most powerful and energetic phenomena of our Universe. The Astrorivelatore Gamma ad Immagini LEggero (AGILE) Gamma-ray Mission was launched in 2007 with the aim of observing celestial sources by means of three instruments covering a wide range of energies, from hard X-rays up to 30 GeV. Thanks to its wide field of view, AGILE set to observe and detect emission from pulsars, pulsar wind nebulae, gamma-ray bursts, active galactic nuclei, fast radio bursts, terrestrial gamma-ray flashes, and the electromagnetic counterparts of neutrinos and gravitational waves. In particular, the fast on-ground processing and analysis chain allowed the AGILE team to promptly respond to transient events, and activate or participate in multiwavelength observing campaigns. Eventually, after 17 years of operations, the AGILE Italian scientific satellite re-entered the atmosphere on 14 February 2024, ending its intense activity as a hunter of some of the most energetic cosmic sources in the Universe that emit X and &gamma;-rays. We will review the most relevant AGILE results to date and their impact on the advancements of theoretical models.

]]>Universe doi: 10.3390/universe10040152

Authors: Orhan Donmez Fatih Dogan

To explain the observed X-ray data in a black hole&ndash;accreting matter system and understand the physical mechanisms behind QPOs, we have numerically modeled the dynamical and oscillation properties of the shock cone formed around both slowly and rapidly rotating Hartle&ndash;Thorne black holes, resulting from the mechanism of Bondi&ndash;Hoyle&ndash;Lyttleton (BHL). According to the numerical simulations, an increase in the quadrupole parameter leads to a decrease in the shock cone opening angle around the black hole. A larger quadrupole parameter results in more matter falling into the black hole within the cone. The combination of the quadrupole parameter and black hole rotation causes the matter inside the cone to exhibit chaotic motion. These dynamical changes and chaotic behavior of the shock cones excite the fundamental oscillation modes. Moreover, new frequencies have been formed due to the nonlinear coupling of the fundamental modes. Conversely, we have numerically studied the behavior of cones formed around rapidly rotating Hartle&ndash;Thorne black holes and found differences and similarities to those obtained from slowly rotating cases. Finally, comparing the outcomes obtained fromHartle&ndash;Thorne gravity with the results fromKerr and Einstein&ndash;Gauss&ndash;Bonnet (EGB) gravities reveals the impact of the quadrupole parameter on the shock cone and QPOs.

]]>Universe doi: 10.3390/universe10030151

Authors: Gianni Pascoli

Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the &kappa;-model. An additional connection, between the &kappa;-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter, a0, appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and &kappa;-model) and/or to the dimension of the object under consideration (NFDG and &kappa;-model). We then confer to parameter a0 a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the &kappa;-model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The &kappa;-model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database.

]]>Universe doi: 10.3390/universe10030150

Authors: Hyun Seok Yang

We present a novel background-independent framework for cosmic inflation, starting with a matrix model. In this framework, inflation is portrayed as a dynamic process responsible for the generation of both space and time. This stands in contrast to conventional inflation, which is characterized as a mere (exponential) expansion of an already existing spacetime, driven by the vacuum energy associated with an inflaton field. We observe that the cosmic inflation is triggered by the condensate of Planck energy into a vacuum and responsible for the dynamical emergence of spacetime. The emergent spacetime picture admits a background-independent formulation so that the inflation is described by a conformal Hamiltonian system which requires neither an inflaton field nor an ad hoc inflation potential. This implies that the emergent spacetime may incapacitate all the rationales to introduce the multiverse hypothesis.

]]>Universe doi: 10.3390/universe10030149

Authors: Damiano F. G. Fiorillo

The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a diffuse flux of astrophysical neutrinos in the TeV-PeV energy range, likely produced in astrophysical sources accelerating cosmic rays, and more recently it has reported on a few candidate individual neutrino sources. Future experiments will be able to improve on these measurements quantitatively, by the detection of more events, and qualitatively, by extending the measurement into the EeV energy range. In this paper, we review the main features of the neutrino emission and sources observed by IceCube, as well as the main candidate sources that could contribute to the diffuse neutrino flux. As a parallel question, we review the status of high-energy neutrinos as a probe of Beyond the Standard Model physics coupling to the neutrino sector.

]]>Universe doi: 10.3390/universe10030148

Authors: Luca Boccioli Lorenzo Roberti

Recent developments in multi-dimensional simulations of core-collapse supernovae have considerably improved our understanding of this complex phenomenon. In addition to that, one-dimensional (1D) studies have been employed to study the explosion mechanism and its causal connection to the pre-collapse structure of the star, as well as to explore the vast parameter space of supernovae. Nonetheless, many uncertainties still affect the late stages of the evolution of massive stars, their collapse, and the subsequent shock propagation. In this review, we will briefly summarize the state-of-the-art of both 1D and 3D simulations and how they can be employed to study the evolution of massive stars, supernova explosions, and shock propagation, focusing on the uncertainties that affect each of these phases. Finally, we will illustrate the typical nucleosynthesis products that emerge from the explosion.

]]>Universe doi: 10.3390/universe10030147

Authors: Victor Berezin Inna Ivanova

The action of an ideal fluid in Euler variables with a variable number of particles is used for the phenomenological description of the processes of particle creation in strong external fields. It has been demonstrated that the conformal invariance of the creation law imposes quite strict restrictions on the possible types of sources. It is shown that combinations with the particle number density in the creation law can be interpreted as dark matter within the framework of this model.

]]>Universe doi: 10.3390/universe10030146

Authors: Salvatore Scuderi

The ASTRI Mini-Array is an Istituto Nazionale di Astrofisica (INAF) project to build and operate an array of nine Imaging Atmospheric Cherenkov Telescopes (IACTs) at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias in Tenerife (Spain) based on a host agreement with INAF and, as such, it will be the largest IACT array until the Cherenkov Telescope Array Observatory starts operations. Implementing the ASTRI Mini-Array poses several challenges from technical, logistic, and management points of view. Starting from the description of the innovative technologies adopted to build the telescopes, we will discuss the solutions adopted to overcome these challenges, making the ASTRI Mini-Array a great instrument to perform deep observations of the galactic and extra-galactic sky at very high energies.

]]>Universe doi: 10.3390/universe10030145

Authors: Siyang Zhang Shuquan Wang

This paper investigates the trajectory design problem in the scenario of a multiple Sun-synchronous Orbit (SSO) space debris flyby mission from a DRO space station. At first, the characteristics of non-planar transfer from DRO to SSO in the Earth&ndash;Moon system are analyzed. The methods of large-scale ergodicity and pruning are utilized to investigate single-impulse and two-impulse DRO&ndash;Earth transfers. Using a powered lunar flyby, the two-impulse DRO&ndash;Earth transfer is able to fly by SSO debris while satisfying the requirements of the mission. After the local optimization, the optimal result of two-impulse DRO&ndash;Earth transfer and flyby is obtained. A multi-objective evolutionary algorithm is used to design the Pareto-optimal trajectories of multiple flybys. The semi-analytical optimization method is developed to provide the estimations of the transfer parameters in order to reduce the computations caused by the evolutionary algorithm. Simulations show that transferring from the 3:2 resonant DRO to a near-coplanar flyby of a SSO target debris using a powered lunar gravity assist needs a 0.47 km/s velocity increment. The mission&rsquo;s total velocity increment is 1.39 km/s, and the total transfer time is 2.23 years.

]]>Universe doi: 10.3390/universe10030144

Authors: Kazuharu Bamba

Various precise cosmological observations, e [...]

]]>Universe doi: 10.3390/universe10030143

Authors: Wolfgang Oehm Pavel Kroupa

Simulations of structure formation in the standard cold dark matter cosmological model quantify the dark matter halos of galaxies. Taking into account dynamical friction between dark matter halos, we investigate the past orbital dynamical evolution of the Magellanic Clouds in the presence of the Galaxy. Our calculations are based on a three-body model of rigid Navarro&ndash;Frenk&ndash;White profiles for dark matter halos but were verified in a previous publication by comparison to high-resolution N-body simulations of live self-consistent systems. Under the requirement that the LMC and SMC had an encounter within 20 kpc between 1 and 4 Gyr ago in order to allow the development of the Magellanic Stream, using the latest astrometric data, the dynamical evolution of the MW/LMC/SMC system is calculated backwards in time. With the employment of the genetic algorithm and a Markov-Chain Monte-Carlo method, the present state of this system is unlikely, with a probability of &lt;10&minus;9 (6&sigma; complement), because the solutions found do not fit into the error bars for the observed plane-of-sky velocity components of the Magellanic Clouds. This implies that orbital solutions that assume dark matter halos, according to cosmological structure formation theory, to exist around the Magellanic Clouds and the Milky Way are not possible with a confidence of more than 6 sigma.

]]>Universe doi: 10.3390/universe10030142

Authors: Jaume Giné Giuseppe Gaetano Luciano

The emergence of a minimal observable length of order of the Planck scale is a prediction of many quantum theories of gravity. However, the question arises as to whether this is a real fundamental length affecting nature in all of its facets, including spacetime. In this work, we show that the quantum measurement process implies the existence of a minimal measurable length and consequently the apparent discretization of spacetime. The obtained result is used to infer the value of zero-point energy in the universe, which is found to be in good agreement with the observed cosmological constant. This potentially offers some hints towards the resolution of the cosmological constant problem.

]]>Universe doi: 10.3390/universe10030141

Authors: Andrea Lapi Giovanni Gandolfi Lumen Boco Francesco Gabrielli Marcella Massardi Balakrishna S. Haridasu Carlo Baccigalupi Alessandro Bressan Luigi Danese

We aim to constrain the stellar initial mass function (IMF) during the epoch of reionization. To this purpose, we build up a semi-empirical model for the reionization history of the Universe based on various ingredients: the latest determination of the UV galaxy luminosity function from JWST out to redshift z&#8818;12; data-inferred and simulation-driven assumptions on the redshift-dependent escape fraction of ionizing photons from primordial galaxies; a simple yet flexible parameterization of the IMF &#981;(m&#8902;)&sim;m&#8902;&xi;e&minus;m&#8902;,c/m&#8902; in terms of a high-mass end slope &xi;&lt;0 and a characteristic mass m&#8902;,c, below which a flattening or a bending sets in (allowing description of a variety of IMF shapes from the classic Salpeter to top-heavy ones); the PARSEC stellar evolution code to compute the UV and ionizing emission from different stars&rsquo; masses as a function of age and metallicity; and a few physical constraints related to stellar and galaxy formation in faint galaxies at the reionization redshifts. We then compare our model outcomes with the reionization observables from different astrophysical and cosmological probes and perform Bayesian inference on the IMF parameters via a standard MCMC technique. We find that the IMF slope &xi; is within the range from &minus;2.8 to &minus;2.3, consistent with direct determination from star counts in the Milky Way, while appreciably flatter slopes are excluded at great significance. However, the bestfit value of the IMF characteristic mass m&#8902;,c&sim;a few M&#8857; implies a suppression in the formation of small stellar masses at variance with the IMF in the local Universe. This may be induced by the thermal background of &sim;20&ndash;30 K provided by CMB photons at the reionization redshifts. We check that our results are robust against different parameterizations for the redshift evolution of the escape fraction. Finally, we investigate the implications of our reconstructed IMF for the recent JWST detections of massive galaxies at and beyond the reionization epoch, showing that any putative tension with the standard cosmological framework is substantially alleviated.

]]>Universe doi: 10.3390/universe10030140

Authors: Salvatore Capozziello Giuseppe Sarracino Giulia De Somma

A critical discussion on the H0 Hubble constant tension is presented by considering both early and late-type observations. From recent precise measurements, discrepancies emerge when comparing results for some cosmological quantities obtained at different redshifts. We highlight the most relevant measurements of H0 and propose potential ideas to solve its tension. These solutions concern the exploration of new physics beyond the &Lambda;CDM model or the evaluation of H0 by other methods. In particular, we focus on the role of the look-back time.

]]>Universe doi: 10.3390/universe10030139

Authors: Alisher Aitbayev

The Beam Energy Scan (BES) program at RHIC aims to explore the QCD phase diagram, including the search for the evidence of the 1st order phase transition from hadronic matter to Quark-Gluon Plasma (QGP) and the location of the QCD critical point. One of the features previously observed in the study of QGP is the effect of suppression of particle production with high transverse momenta pT (&gt;2 GeV/c) at energies sNN = 62.4&ndash;200 GeV, which was deduced from the charged-particle nuclear modification factor (RCP) measured using the data from Beam Energy Scan Program Phase I (BES-I) of STAR experiment. In 2018, STAR has collected over 500 million events from Au+Au collisions at sNN = 27 GeV as a part of the STAR BES-II program, which is about a factor of 10 higher than BES-I 27 GeV data size. In this report, we present new measurements of charged particle production and the nuclear modification factor RCP, from this new 27 GeV data set and compare them with the BES-I results. The new measurements extend the previous BES-I results to higher transverse momentum range, which allows better exploration of the jet quenching effects at low RHIC energies, and may help to understand the effects of the formation and properties of QGP at these energies.

]]>Universe doi: 10.3390/universe10030138

Authors: Euaggelos E. Zotos Eman M. Moneer Tobias C. Hinse

We investigate the orbital dynamics of an exosystem consisting of a solar-mass host star, a transiting body, and an Earth-size exoplanet within the framework of the generalized three-body problem. Depending on its mass, the transiting body can either be a super-Jupiter or a brown dwarf. To determine the final states of the Earth-size exoplanet, we conduct a systematic and detailed classification of the available phase space trajectories. Our classification scheme distinguishes between the bounded, escape, and collisional motions of the Earth-size exoplanet. Additionally, for cases of ordered (regular) motion, we further categorize the associated initial conditions based on the geometry of their respective trajectories. These bounded regular trajectories hold significant importance as they provide insights into the regions of phase space where the motion of the Earth-size exoplanet can be dynamically stable. Of particular interest is the identification of initial conditions that result in a bounded exomoon-like orbit of the Earth-size exoplanet around the transiting body.

]]>Universe doi: 10.3390/universe10030137

Authors: Alexander Kamenshchik Polina Petriakova

We apply a very simple procedure to construct non-singular cosmological models for flat Friedmann universes filled with minimally coupled scalar fields or by tachyon Born&ndash;Infeld-type fields. Remarkably, for the minimally coupled scalar field and the tachyon field, the regularity of the cosmological evolution, or in other words, the existence of bounce, implies the necessity of the transition between scalar fields with standard kinetic terms to those with phantom ones. In both cases, the potentials in the vicinity of the point of the transition have a non-analyticity of the cusp form that is characterized by the same exponent and is equal to 23. If, in the tachyon model&rsquo;s evolution, the pressure changes its sign, then another transformation of the Born&ndash;Infeld-type field occurs: the tachyon transforms into a pseudotachyon, and vice versa. We also undertake an analysis of the stability of the cosmological evolution in our models; we rely on the study of the speed of sound squared.

]]>Universe doi: 10.3390/universe10030136

Authors: Alexandre Landry Fayçal Hammad Reza Saadati

The quantum Hall effect under the influence of gravity and inertia is studied in a unified way. We make use of an algebraic approach, as opposed to an analytic approach. We examine how both the integer and the fractional quantum Hall effects behave under a combined influence of gravity and inertia using a unified Hamiltonian. For that purpose, we first re-derive, using the purely algebraic method, the energy spectrum of charged particles moving in a plane perpendicular to a constant and uniform magnetic field either (i) under the influence of a nonlinear gravitational potential or (ii) under the influence of a constant rotation. The general Hamiltonian for describing the combined effect of gravity, rotation and inertia on the electrons of a Hall sample is then built and the eigenstates are obtained. The electrons mutual Coulomb interaction that gives rise to the familiar fractional quantum Hall effect is also discussed within such a combination.

]]>Universe doi: 10.3390/universe10030135

Authors: Rajan Gupta

A survey of the calculations of the isovector axial vector form factor of the nucleon using lattice QCD is presented. Attention is paid to statistical and systematic uncertainties, in particular those due to excited state contributions. Based on a comparison of results from various collaborations, a case is made that lattice results are consistent within 10%. A similar level of uncertainty is in the axial charge gAu&minus;d, the mean squared axial charge radius &#10216;rA2&#10217;, the induced pseudoscalar charge gP&lowast;, and the pion&ndash;nucleon coupling g&pi;NN. Even with the current methodology, a significant reduction in errors is expected over the next few years with higher statistics data on more ensembles closer to the physical point. Lattice QCD results for the form factor GA(Q2) are compatible with those obtained from the recent MINER&nu;A experiment but lie 2&ndash;3&sigma; higher than the phenomenological extraction from the old &nu;&ndash;deuterium bubble chamber scattering data for Q2&gt;0.3 GeV2. Current data show that the dipole ansatz does not have enough parameters to fit the form factor over the range 0&le;Q2&le;1 GeV2, whereas even a z2 truncation of the z expansion or a low order Pad&eacute; are sufficient. Looking ahead, lattice QCD calculations will provide increasingly precise results over the range 0&le;Q2&le;1 GeV2, and MINER&nu;A-like experiments will extend the range to Q2&sim;2 GeV2 or higher. Nevertheless, improvements in lattice methods to (i) further control excited state contributions and (ii) extend the range of Q2 are needed.

]]>Universe doi: 10.3390/universe10030134

Authors: Francisco A. Brito Carlos H. A. B. Borges José A. V. Campos Francisco G. Costa

We consider f(R,T) modified theories of gravity in the context of string-theory-inspired dilaton gravity. We deal with a specific model that under certain conditions describes the late time Universe in accord with observational data in modern cosmology and addresses the H0 tension. This is done by exploring the space of parameters made out of those coming from the modified gravity and dilatonic charge sectors. We employ numerical methods to obtain several important observable quantities.

]]>Universe doi: 10.3390/universe10030133

Authors: Ziqiang Cai Ming Liu Wen-Qian Wang Tong-Yu He Zhan-Wen Han Rong-Jia Yang

We consider geodesic motions in Kerr&ndash;Sen&ndash;AdS4 spacetime. We obtain equations of motion for light rays and test particles. Using parametric diagrams, we show some regions where radial and latitudinal geodesic motions are allowed. We analyze the impact of parameters related to the dilatonic scalar on the orbit and find that it will result in more rich and complex orbital types.

]]>Universe doi: 10.3390/universe10030132

Authors: Ashutosh Dwibedi Nandita Padhan Arghya Chatterjee Sabyasachi Ghosh

The present review article has attempted a compact formalism description of transport coefficient calculations for relativistic fluid, which is expected in heavy ion collision experiments. Here, we first address the macroscopic description of relativistic fluid dynamics and then its microscopic description based on the kinetic theory framework. We also address different relaxation time approximation-based models in Boltzmann transport equations, which make a sandwich between Macro and Micro frameworks of relativistic fluid dynamics and finally provide different microscopic expressions of transport coefficients like the fluid&rsquo;s shear viscosity and bulk viscosity. In the numeric part of this review article, we put stress on the two gross components of transport coefficient expressions: relaxation time and thermodynamic phase-space part. Then, we try to tune the relaxation time component to cover earlier theoretical estimations and experimental data-driven estimations for RHIC and LHC matter. By this way of numerical understanding, we provide the final comments on the values of transport coefficients and relaxation time in the context of the (nearly) perfect fluid nature of the RHIC or LHC matter.

]]>Universe doi: 10.3390/universe10030131

Authors: Andrey A. Grib Yuri V. Pavlov

During particle collisions in the vicinity of the horizon of black holes, it is possible to achieve energies and temperatures corresponding to phase transitions in particle physics. It is shown that the sizes of the regions of the new phase are of the order of the Compton length for the corresponding mass scale. The lifetime is also on the order of the Compton time. It is shown that the inverse influence of the energy density in the electro-weak phase transition in collisions on the space&ndash;time metric can be neglected.

]]>Universe doi: 10.3390/universe10030130

Authors: Gang Cao Xiongbang Yang Li Zhang

We review the recent advances in the pulsar high-energy &gamma;-ray observation and the electrodynamics of the pulsar magnetospheres from the early vacuum model to the recent plasma-filled models by numerical simulations. The numerical simulations have made significant progress toward the self-consistent modeling of the plasma-filled magnetosphere by including the particle acceleration and radiation. The current numerical simulations confirm a near force-free magnetosphere with the particle acceleration in the separatrix near the light cylinder and the current sheet outside the light cylinder, which can provide a good match to the recent high-energy &gamma;-ray observations. The modeling of the combined multi-wavelength light curves, spectra, and polarization are expected to provide a stronger constrain on the geometry of the magnetic field lines, the location of the particle acceleration and the emission region, and the emission mechanism in the pulsar magnetospheres.

]]>Universe doi: 10.3390/universe10030129

Authors: Lior Shamir

Recent puzzling observations, such as the H0 tension, large-scale anisotropies, and massive disk galaxies at high redshifts, have been challenging the standard cosmological model. While one possible explanation is that the standard model is incomplete, other theories are based on the contention that the redshift model as a distance indicator might be biased. These theories can explain the recent observations, but they are challenged by the absence of a direct empirical reproducible observation that the redshift model can indeed be inconsistent. Here, I describe a simple experiment that shows that the spectra of galaxies depend on their rotational velocity relative to the rotational velocity of the Milky Way. Moreover, it shows that the redshift of galaxies that rotate in the opposite direction relative to the Milky Way is significantly smaller compared with the redshift of galaxies that rotate in the same direction relative to the Milky Way (p &lt; 0.006). Three different datasets were used independently, each one was prepared in a different manner, and all of them showed similar redshift bias. A fourth dataset of galaxies from the Southern Galactic pole was also analyzed and shows similar results. All four datasets are publicly available. While a maximum average z difference of &sim;0.012 observed with galaxies of relatively low redshift (z &lt; 0.25) is not extreme, the bias is consistent and canpotentially lead to explanations to puzzling observations such as the H0 tension.

]]>Universe doi: 10.3390/universe10030128

Authors: Jameel-Un Nabi Muhammad Riaz Arslan Mehmood

&beta;-decay is one of the key factors for understanding the r-process and evolution of massive stars. The Gamow&ndash;Teller (GT) transitions drive the &beta;-decay process. We employ the proton&ndash;neutron quasiparticle random phase approximation (pn-QRPA) model to calculate terrestrial and stellar &beta;-decay rates for 50 top-ranked nuclei possessing astrophysical significance according to a recent survey. The model parameters of the pn-QRPA model affect the predicted results of &beta;-decay. The current study investigates the effect of nucleon&ndash;nucleon pairing gaps on charge-changing transitions and the associated &beta; decay rates. Three different values of pairing gaps, namely TF, 3TF, and 5TF, were used in our investigation. It was concluded that both GT strength distributions and half-lives are sensitive to pairing gap values. The 3TF pairing gap scheme, in our chosen nuclear model, resulted in the best prediction with around 80% of the calculated half-lives within a factor 10 of the measured ones. The 3TF pairing scheme also led to the calculation of the biggest &beta;-decay rates in stellar matter.

]]>Universe doi: 10.3390/universe10030127

Authors: Tamás Csörgő Sándor Hegyi István Szanyi

A simple L&eacute;vy &alpha;-stable (SL) model is used to describe the data on elastic pp and pp&macr; scattering at low-|t| from SPS energies up to LHC energies. The SL model is demonstrated to describe the data with a strong non-exponential feature in a statistically acceptable manner. The energy dependence of the parameters of the model is determined and analyzed. The L&eacute;vy &alpha; parameter of the model has an energy-independent value of 1.959 &plusmn; 0.002 following from the strong non-exponential behavior of the data. We strengthen the conclusion that the discrepancy between TOTEM and ATLAS elastic pp differential cross section measurements arises only in the normalization and not in the shape of the distribution of the data as a function of t. We find that the slope parameter has different values for pp and pp&macr; elastic scattering at LHC energies. This may be the effect of the odderon exchange or the jump in the energy dependence of the slope parameter in the energy interval 3 GeV &#8818;s&#8818; 4 GeV.

]]>Universe doi: 10.3390/universe10030126

Authors: Zhaozhong Shi

The sPHENIX experiment is a state-of-the-art jet and heavy flavor physics detector, which successfully recorded its first Au + Au collision data at 200 GeV at the Relativistic Heavy Ion Collider (RHIC). sPHENIX will provide heavy flavor physics measurements at RHIC, covering an unexplored kinematic region and unprecedented precision, to probe the parton energy loss mechanism, parton transport coefficients in quark&ndash;gluon plasma, and the hadronization process under various medium conditions. At the center of sPHENIX, the monolithic active pixel sensor (MAPS)-based VerTeX detector (MVTX) is a high-precision silicon pixel detector. The MVTX provides excellent position resolution and the capability of operating in continuous streaming readout mode, allowing precise vertex determination and recording a large data sample, both of which are particularly crucial for heavy flavor physics measurements. In this work, we will show the general performance of heavy-flavor hadron reconstruction. In addition, we will discuss the commissioning experience with sPHENIX. Finally, we will provide the projection of b-hadron and jet observables and discuss the estimated constraints on theoretical models.

]]>Universe doi: 10.3390/universe10030125

Authors: Jaydeep Kumar Basak Vinay Malvimat Himanshu Parihar Boudhayan Paul Gautam Sengupta

We demonstrate the equivalence of two different conjectures in the literature for the holographic entanglement negativity in AdS3/CFT2, modulo certain constants. These proposals involve certain algebraic sums of bulk geodesics homologous to specific combinations of subsystems, and the entanglement wedge cross section (EWCS) backreacted by a cosmic brane for the conical defect geometry in the bulk gravitational path integral. It is observed that the former conjectures reproduce the field theory replica technique results in the large central charge limit whereas the latter involves constants related to the Markov gap. In this context, we establish an alternative construction for the EWCS of a single interval in a CFT2 at a finite temperature to resolve an issue for the latter proposal involving thermal entropy elimination for holographic entanglement negativity. Our construction for the EWCS correctly reproduces the corresponding field theory results modulo the Markov gap constant in the large central charge limit.

]]>Universe doi: 10.3390/universe10030124

Authors: Efe Yazgan Pedro Silva

This Special Issue of Universe is devoted to the most massive fundamental elementary particle known, the top quark [...]

]]>Universe doi: 10.3390/universe10030123

Authors: Felix Finster José M. Isidro Claudio F. Paganini Tejinder P. Singh

The present paper is a modest attempt to initiate the research program outlined in this abstract. We propose that general relativity and relativistic MOND (RelMOND) are analogues of broken electroweak symmetry. That is, SU(2)R&times;U(1)YDEM&rarr;U(1)DEM (DEM stands for dark electromagnetism), and GR is assumed to arise from the broken SU(2)R symmetry and is analogous to the weak force. RelMOND is identified with dark electromagnetism U(1)DEM, which is the remaining unbroken symmetry after the spontaneous symmetry breaking of the dark electro-grav sector SU(2)R&times;U(1)YDEM. This sector, as well as the electroweak sector, arises from the breaking of an E8&times;E8 symmetry in a recently proposed model of unification of the standard model with pre-gravitation, with the latter based on an SU(2)R gauge theory. The source charge for the dark electromagnetic force is the square root of mass, motivated by the experimental fact that the ratio of the square roots of the masses of the electron, up-quark, and down-quark is 1:2:3, which is the opposite of the ratio of their electric charges at 3:2:1. The introduction of the dark electromagnetic force helps us understand the peculiar mass ratios of the second and third generations of charged fermions. We also note that in the deep MOND regime, acceleration is proportional to the square root of mass, which motivates us to propose the relativistic U(1)DEM gauge symmetry as the origin of MOND. We explain why the dark electromagnetic force falls inversely with distance, as in MOND, rather than following the inverse square of distance. We conclude that dark electromagnetism effectively mimics cold dark matter, and the two are essentially indistinguishable in cosmological situations where CDM successfully explains observations, such as CMB anisotropies and gravitational lensing.

]]>Universe doi: 10.3390/universe10030122

Authors: Olga Avsajanishvili Gennady Y. Chitov Tina Kahniashvili Sayan Mandal Lado Samushia

Scalar field &#981;CDM models provide an alternative to the standard &Lambda;CDM paradigm, while being physically better motivated. Dynamical scalar field &#981;CDM models are divided into two classes: the quintessence (minimally and non-minimally interacting with gravity) and phantom models. These models explain the phenomenology of late-time dark energy. In these models, energy density and pressure are time-dependent functions under the assumption that the scalar field is described by the ideal barotropic fluid model. As a consequence of this, the equation of state parameter of the &#981;CDM models is also a time-dependent function. The interaction between dark energy and dark matter, namely their transformation into each other, is considered in the interacting dark energy models. The evolution of the universe from the inflationary epoch to the present dark energy epoch is investigated in quintessential inflation models, in which a single scalar field plays a role of both the inflaton field at the inflationary epoch and of the quintessence scalar field at the present epoch. We start with an overview of the motivation behind these classes of models, the basic mathematical formalism, and the different classes of models. We then present a compilation of recent results of applying different observational probes to constraining &#981;CDM model parameters. Over the last two decades, the precision of observational data has increased immensely, leading to ever tighter constraints. A combination of the recent measurements favors the spatially flat &Lambda;CDM model but a large class of &#981;CDM models is still not ruled out.

]]>Universe doi: 10.3390/universe10030121

Authors: Rafel Jaume Rodrigo Tenorio Alicia M. Sintes

Continuous gravitational-wave (CW) signals are long-lasting quasi-monochromatic gravitational-wave signals expected to be emitted by rapidly rotating non-axisymmetric neutron stars. Depending on the rotational frequency and sky location of the source, certain CW signals may behave in a similar manner to narrow-band artifacts present in ground-based interferometric detectors. Part of the detector characterization tasks in the current generation of interferometric detectors (Advanced LIGO, Advanced Virgo, and KAGRA) aim at understanding the origin of these narrow artifacts, commonly known as "spectral lines". It is expected that similar tasks will continue after the arrival of next-generation detectors (e.g., Einstein Telescope and Cosmic Explorer). Typically, a fraction of the observed lines in a given detector can be associated to one or more instrumental causes; others, however, have an unknown origin. In this work, we assess the similarity of CW signals to spectral lines in order to understand whether a CW signal may be mistaken for a noise artifact. Albeit astrophysically unlikely, our results do not rule out the possibility of a CW signal being visible in the detector&rsquo;s power spectrum.

]]>Universe doi: 10.3390/universe10030120

Authors: Nicolás Cuello Mario Sucerquia

In the original publication [...]

]]>Universe doi: 10.3390/universe10030119

Authors: Galina L. Klimchitskaya Vladimir M. Mostepanenko

This review considers the theoretical approaches to the understanding of dark energy, which comprises approximately 68% of the energy of our Universe and explains the acceleration in its expansion. Following a discussion of the main approach based on Einstein&rsquo;s equations with the cosmological term, the explanations of dark energy using the concept of some kind of scalar field are elucidated. These include the concept of a quintessence and modifications of the general theory of relativity by means of the scalar&ndash;tensor gravity exploiting the chameleon, symmetron and environment-dependent dilaton fields and corresponding particles. After mentioning several laboratory experiments allowing us to constrain the hypothetical scalar fields modeling the dark energy, special attention is devoted to the possibility of constraining the parameters of chameleon, symmetron and environment-dependent dilaton fields from measuring the Casimir force. It is concluded that the parameters of each of these fields can be significantly strengthened in near future by using the next-generation setups in preparation suitable for measuring the Casimir force at larger separations.

]]>Universe doi: 10.3390/universe10030118

Authors: Sharang Rav Sharma

We report the measurement of first-order event plane-correlated directed flow (v1) and triangular flow (v3) for identified hadrons (&pi;&plusmn;, K&plusmn;, and p), net particle (net-K, net-p), and light nuclei (d and t) in Au + Au collisions at sNN = 3.2, 3.5, and 3.9 GeV in the fixed-target mode from the second phase of the beam energy scan (BES-II) program at RHIC-STAR. The v1 slopes at mid-rapidity for identified hadrons and net particles except &pi;+ are found to be positive, implying the effect of dominant repulsive baryonic interactions. The slope of v1 for net-kaon undergoes a sign change from negative to positive at a lower collision energy compared to net-proton. An approximate atomic mass number scaling is observed in the measured v1 slopes of light nuclei at mid-rapidity, which favors the nucleon coalescence mechanism for the production of light nuclei. The v3 slope for all particles decreases in magnitude with increasing collision energy, suggesting a notable integrated impact of the mean-field, baryon stopping, and collision geometry at lower collision energies.

]]>Universe doi: 10.3390/universe10030117

Authors: Jean-Pierre Gazeau

Physical laws manifest themselves through the amalgamation of mathematical symbols, numbers, functions, geometries, and relationships. These intricate combinations unfold within a mathematical model devised to capture and represent the &ldquo;objective reality&rdquo; of the system under examination. In this symbiotic relationship between physics and mathematics, the language of mathematics becomes a powerful tool for describing and predicting the behavior of the physical world. The language used and the associated concepts are in a perpetual state of evolution, mirroring the ongoing expansion of the phenomena accessible to our scientific understanding. In this contribution, written in honor of Richard Kerner, we delve into fundamental, at times seemingly elementary, elements of the mathematical language inherent to the physical sciences, guided by the overarching principles of symmetry and group theory. Our focus turns to the captivating realm of spheres, those strikingly symmetric entities that manifest prominently within our geometric landscape. By exploring the interplay between mathematical abstraction and the tangible beauty of symmetry, we seek to deepen our understanding of the underlying structures that govern our interpretation of the physical world.

]]>Universe doi: 10.3390/universe10030116

Authors: Andrzej Góźdź Marek Góźdź

Using the projection evolution (PEv) approach, time can be included in quantum mechanics as an observable. Having the time operator, it is possible to explore the temporal structure of various quantum events. In the present paper, we discuss the possibility of constructing a quantum clock which advances in time during its quantum evolution, in each step having some probability to localize itself on the time axis in the new position. We propose a working two-state model as the simplest example of such a clock.

]]>Universe doi: 10.3390/universe10030115

Authors: Rachid Ouyed Denis Leahy Nico Koning Prashanth Jaikumar

We propose a non-exotic electromagnetic solution (within the standard model of particle physics) to the cosmological 7Li problem based upon a narrow 2 MeV photo-emission line from the decay of light glueballs (LGBs). These LGBs form within color superconducting quark clusters (SQCs), which are tens of Fermi in size, in the radiation-dominated post-BBN epoch. The mono-chromatic line from the LGB&rarr;&gamma;+&gamma; decay reduces Big Bang nucleosynthesis (BBN) 7Be by 2/3 without affecting other abundances or the cosmic microwave background (CMB) physics, provided the combined mass of the SQCs is greater than the total baryonic mass in the universe. Following the LGB emission, the in-SQC Quantum ChromoDynamics (QCD) vacuum becomes unstable and &ldquo;leaks&rdquo; (via quantum tunneling) into the external space-time (trivial) vacuum, inducing a decoupling of SQCs from hadrons. In seeking a solution to the 7Li problem, we uncovered a solution that also addresses the Dark Energy (DE) and dark matter (DM) problem, making these critical problems intertwined in our model. Being colorless, charge-neutral, optically thin, and transparent to hadrons, SQCs interact only gravitationally, making them a viable cold DM (CDM) candidate. The leakage (i.e., quantum tunneling) of the in-SQC QCD vacuum to the trivial vacuum offers an explanation of DE in our model and allows for a cosmology that evolves into a &Lambda;CDM universe at a low redshift with a possible resolution of the Hubble tension. Our model distinguishes itself by proposing that the QCD vacuum within SQCs possesses the ability to tunnel into the exterior trivial vacuum, resulting in the generation of DE. This implies the possibility that DM and hadrons might represent distinct phases of quark matter within the framework of QCD, characterized by different vacuum properties. We discuss SQC formation in heavy-ion collision experiments at moderate temperatures and the possibility of detection of MeV photons from the LGB&rarr;&gamma;+&gamma; decay.

]]>Universe doi: 10.3390/universe10030114

Authors: Lizhi Liu Yunguo Jiang Junhao Deng Zhaohao Chen Chenli Ma

Variability study at multi-frequency provides us with rich information of the emission and variation mechanism for blazars. In this work, we present a comprehensive multi-frequency analysis of the high-synchrotron-peaked (HSP) blazar Mrk 501, using &gamma;-ray, X-ray, optical, optical polarization, and radio data. The multiple-wavelength light curves are analyzed by using the localized cross-correlation function to derive locations of their emitting regions. The X-ray, &gamma;-ray, and optical emitting regions are found to be upstream of the radio core region, while the X-ray and &gamma;-ray emitting regions likely coincide. We studied the variation behaviors for three long-term (years), five relatively short-term (months) periods. We find a positive correlation between the optical and X-ray fluxes, and conclude that the variable of Doppler factor is not favored for the one-zone SSC scenario. The study also identifies the existence of a soft &gamma;-ray background in the low-activity state, which could be explained by the spine/layer jet model. Our study on Mrk 501 provides valuable insights to understand the emission processes and variation mechanism for HSP blazars.

]]>Universe doi: 10.3390/universe10030113

Authors: Michael L. Walker

We claim that quantum collapse, as per the Copenhagen interpretation of quantum mechanics, follows naturally from the energetics of measurement. We argue that a realistic device generates an interaction energy that drives a random walk in Hilbert space and generates the probabilistic interpretation of Born.

]]>Universe doi: 10.3390/universe10030112

Authors: Kishora Nayak Shu-Su Shi Zi-Wei Lin

Recently, the rapidity-odd directed flow (v1) of produced hadrons (K&minus;, &#981;, p&macr;, &Lambda;&macr;, &Xi;&macr;+, &Omega;&minus;, and &Omega;&macr;+) has been studied. Several combinations of these produced hadrons, with very small mass differences but differences in the net electric charge (&Delta;q) and net strangeness (&Delta;S) on the two sides, have been considered. A difference in v1 between the two sides of these combinations (&Delta;v1) has been proposed as a consequence of the electromagnetic field produced in relativistic heavy-ion collisions, especially if &Delta;v1 increases with &Delta;q. Our study is performed to understand the effect of the coalescence sum rule (CSR) on &Delta;v1. We point out that the CSR leads to &Delta;v1=cq&Delta;q+cS&Delta;S, where the coefficients cq and cS reflect the &Delta;v1 of produced quarks. Equivalently, one can write &Delta;v1=cq&Delta;q+cB&Delta;B, involving the difference in the net baryon number &Delta;B, where the CSR gives cB=&minus;3cS. We then propose two methods to extract the coefficients for the &Delta;q and &Delta;S dependences of &Delta;v1.

]]>Universe doi: 10.3390/universe10030111

Authors: Paolo Cea

An attempt is made to describe from first principles the large-scale structure of the confining vacuum in quantum chromodynamics. Starting from our previous variational studies of the SU(2) pure gauge theory in an external Abelian chromomagnetic field and extending Feynman&rsquo;s qualitative analysis in (2+1)-dimensional SU(2) gauge theory, we show that the SU(3) vacuum in three-space and one-time dimensions behaves like a disordered chromomagnetic condensate. Color confinement is assured by the presence of a mass gap together with the absence of color long-range correlations. We offer a clear physical picture for the formation of the flux tube between static quark charges that allows us to determine the color structure and the transverse profile of the flux-tube chromoelectric field. The transverse profile of the flux-tube chromoelectric field turns out to be in reasonable agreement with lattice data. We, also, show that our quantum vacuum allows for both the color and ordinary Meissner effect. We find that for massless quarks, the quantum vacuum can accommodate a finite non-zero density of fermion zero modes leading to the dynamical breaking of the chiral symmetry.

]]>Universe doi: 10.3390/universe10030110

Authors: Gyula M. Szabó Jean Schneider Zoltán Dencs Szilárd Kálmán

After 25 years of the prediction of the possibility of observations, and despite the many hundreds of well-studied transiting exoplanet systems, we are still waiting for the announcement of the first confirmed exomoon. We follow the &ldquo;cascade&rdquo; structure of the Drake equation but apply it to the chain of events leading to a successful detection of an exomoon. The scope of this paper is to reveal the structure of the problem, rather than to give a quantitative solution. We identify three important steps that can lead us to discovery. The steps are the formation, the orbital dynamics and long-term stability, and the observability of a given exomoon in a given system. This way, the question will be closely related to questions of star formation, planet formation, five possible pathways of moon formation; long-term dynamics of evolved planet systems involving stellar and planetary rotation and internal structure; and the proper evaluation of the observed data, taking the correlated noise of stellar and instrumental origin and the sampling function also into account. We highlight how a successful exomoon observation and the interpretations of the expected further measurements prove to be among the most complex and interdisciplinary questions in astrophysics.

]]>Universe doi: 10.3390/universe10030109

Authors: Deepa Thomas Fabio Colamaria

The study of angular correlations of heavy-flavor particles in hadronic collisions can provide crucial insight into the heavy quark production, showering, and hadronization processes. The comparison with model predictions allows us to discriminate among different approaches for heavy quark production and hadronization, as well as different treatments of the underlying event employed by the models to reproduce correlation observables. In ultra-relativistic heavy-ion collisions, where a deconfined state of matter, the quark&ndash;gluon plasma (QGP), is created, heavy-flavor correlations can shed light on the modification of the heavy quark fragmentation due to the interaction between charm and beauty quarks with the QGP constituents, as well as characterize their energy loss processes while traversing the medium. Insight into the possible emergence of collective-like mechanisms in smaller systems, resembling those observed in heavy-ion collisions, can also be obtained by performing correlation studies in high-multiplicity proton&ndash;proton and proton&ndash;nucleus collisions. In this review, the most recent and relevant measurements of heavy-flavor correlations performed in all collision systems at the LHC and RHIC will be presented, and the new understandings that they provide will be discussed.

]]>Universe doi: 10.3390/universe10030108

Authors: Mikhail Piotrovich Serguei Krasnikov Stanislava Buliga Tinatin Natsvlishvili

The existence of even the simplest magnetized wormholes may lead to observable consequences. In the case where both the wormhole and the magnetic field around its mouths are static and spherically symmetric, and gas in the region near the wormhole falls radially into it, the former&rsquo;s spectrum contains bright cyclotron or synchrotron lines due to the interaction of charged plasma particles with the magnetic field. At the same time, due to spherical symmetry, the radiation is non-polarized. The emission of this just-described exotic type (non-thermal, but non-polarized) may be a wormhole signature. Also, in this scenario, the formation of an accretion disk is still quite possible at some distance from the wormhole, but a monopole magnetic field could complicate this process and lead to the emergence of asymmetrical and one-sided relativistic jets.

]]>Universe doi: 10.3390/universe10030107

Authors: Ali Kilcik Jean-Pierre Rozelot Atila Ozguc

In this study, we performed periodicity analyses of selected daily solar (flare index, coronal index, number of coronal mass ejections), geomagnetic (planetary equivalent range index, disturbance storm time index, interplanetary magnetic field) and cosmic ray indices for the last Solar Cycle 24 (from December 2008 to December 2019). To study the periodic variation of the above-listed datasets, the following analysis methods were applied; multi-taper method, Morlet wavelet, cross-wavelet transform and wavelet coherence analysis. The outcome of our analyses revealed the following. (i) The 25&ndash;33 days solar rotation periodicities exist in all datasets without any exception in the MTM power spectra. (ii) Except for the solar rotation periodicity, all periods show data preference, and they appear around the investigated cycle&rsquo;s maximum phase. (iii) When comparing the phase relations between periodicities in the used datasets, they exhibit a gradual transition from small to large periods. For short-term periodicities, there are no phase relations but a mixed phase, whereas for high periodicities, there are complete phase/antiphase transitions. (iv) All identified flare index periodicities are common to all other datasets examined in this investigation.

]]>Universe doi: 10.3390/universe10030106

Authors: Andreas Jung

Recent measurements of the properties of the top quark at the CERN Large Hadron Collider are discussed. The results were measured for single and top quark pair production in their final states, including jets with either one or two leptons or only in hadronic final states. Top quark properties include angular correlations, top quark spin correlations, mass, and width. When looking towards the future, top quark properties open new and even interdisciplinary avenues for probing quantum information science.

]]>Universe doi: 10.3390/universe10030105

Authors: Jianping Yuan Na Wang Shijun Dang Lin Li Feifei Kou Wenming Yan Zhigang Wen Zhiyong Liu Rai Yuen Jingbo Wang Zurong Zhou Peng Liu Dalin He

We present a decade of observations of pulse arrival times for 85 pulsars using the Nanshan radio telescope from July 2002 to March 2014. The Cholesky method can accurately estimate the covariance function of the timing residuals, significantly improving the parameter&rsquo;s estimation accuracy when red noise is prominent. We utilize the Cholesky method to determine positions and basic timing parameters of these pulsars, as well as to obtain timing residuals. Most of these sources showed evidence of significant timing irregularities, which are described. The spectral analyses of timing residuals are presented for pulsars showing obvious red noise. Our results show that timing residuals in half of these pulsars are attributed to rotational irregularities. The red noise in normal pulsars may originate from a random walk in spin frequency or spin-down rate.

]]>Universe doi: 10.3390/universe10030104

Authors: Nicolas Chamel

By compressing matter to densities up to several times the density of atomic nuclei, the catastrophic gravitational collapse of the core of stars with a mass M&#8819;8M&#8857; during supernova explosions and the neutron star left behind (see, e [...]

]]>Universe doi: 10.3390/universe10030103

Authors: Luis Cancino Arancibia Carlos Contreras

We study the interaction of two discrete pomeron fields while considering mass mixing and the general structure of the interaction potential for pomerons within the framework for a functional renormalization group analysis of Reggeon field theory. We find fixed points from the zeros of the beta function establishing the existence of three groups of solutions: the first corresponds to two uncoupled pomerons, the second is a solution known as a &ldquo;pomeron&ndash;odderon&rdquo; interaction, and the final is a real general solution with an interaction potential. We also study its universal properties around this fixed point. This analysis allows for a discussion for the first time on the mixing of two pomerons through renormalization flow paths from the ultraviolet to the non-perturbative infrared regions. Finally, we comment on its role in high-energy scattering.

]]>Universe doi: 10.3390/universe10030102

Authors: Dániel Kincses

Measurements of femtoscopic correlations in high-energy heavy-ion collisions are used to unravel the space&ndash;time structure of the particle-emitting source (the quark&ndash;gluon plasma). Recent results indicate that the pion pair source exhibits a power law behavior and can be described well by a L&eacute;vy distribution. In this study, L&eacute;vy fits were applied to the measured one-dimensional two-pion correlation functions in Au + Au collisions at sNN = 200 GeV. The three extracted source parameters are the L&eacute;vy scale parameter, R, which relates to the size of the source; the correlation strength parameter, &lambda;; and the L&eacute;vy exponent, &alpha;, which characterizes the power law tail of the source. In this paper, we report the current status of the analysis of the extracted L&eacute;vy source parameters and present their dependence on average transverse mass, mT, and on centrality.

]]>Universe doi: 10.3390/universe10020101

Authors: Natalia Gorobey Alexander Lukyanenko Alexander V. Goltsev

An alternative formulation of the no-boundary initial state of the universe in the Euclidean quantum theory of gravity is proposed. Unlike the no-boundary Hartle&ndash;Hawking wave function, in which time appears together with macroscopic space&ndash;time in the semiclassical approximation, in the proposed formalism, time is present from the very beginning on an equal footing with spatial coordinates. The main element of the formalism is the wave functional, which is defined based on the world histories of the universe. This ensures formal 4D covariance of the theory. The wave functional is defined independently of the wave function as an eigenvector of the action operator. The shape of the Origin region, together with the boundary conditions, is determined by the structure of the total energy of the universe, which includes a 3D-invariant contribution of the expansion energy. The own mass of the universe arises as a non-zero value of the expansion energy in the Origin.

]]>Universe doi: 10.3390/universe10020100

Authors: Jinrui Liu Hanxun Wu Qi Liu Yujie Ji Rui Xu Feng Zhang Hu Liu

Angular resolution is crucial for the detailed study of gamma-ray sources and current Cherenkov telescopes (e.g., HESS, MAGIC, and VERITAS) that operate below tens of TeV. Several gamma-ray sources with a photon energy larger than 100 TeV have been revealed by the LHAASO in recent years; the angular resolution of the LHAASO is around&nbsp;0.3&#8728;. A gamma-ray detector with an angular resolution of less than&nbsp;0.1&#8728;&nbsp;operating beyond 100 TeV is needed to study the detailed morphology of ultra-high-energy gamma-ray sources further. The cost-effectiveness is crucial for such large-area detectors. In this paper, the impact of telescope aperture, field of view, pixel size, optical point spread function, and signal integration time window on angular resolution is studied. These results can provide essential elements for the design of telescope arrays.

]]>Universe doi: 10.3390/universe10020099

Authors: Antal Jevicki Xianlong Liu Junjie Zheng

We discuss the large N expansion in backgrounds of extended states with a focus on the implementation of Goldstone symmetries and the construction of the associated Hilbert space. The formulation is given in the general framework of collective field theory. The case of translational symmetry is described first as a basic example. The large N thermofield represents the main topics, with the emergent dynamics of left&ndash;right bulk fields and collective symmetry coordinates. These give the basis for a 1/N expansion.

]]>Universe doi: 10.3390/universe10020098

Authors: Ovidiu Niţescu Stefan Ghinescu Sabin Stoica Fedor Šimkovic

In this paper, we update the phase-space factors for all two-neutrino double electron capture processes. The Dirac&ndash;Hartree&ndash;Fock&ndash;Slater self-consistent method is employed to describe the bound states of captured electrons, enabling a more realistic treatment of atomic screening and more precise binding energies of the captured electrons compared to previous investigations. Additionally, we consider all s-wave electrons available for capture, expanding beyond the K and L1 orbitals considered in prior studies. For light atoms, the increase associated with additional captures compensates for the decrease in decay rate caused by the more precise atomic screening. However, for medium and heavy atoms, an increase in the decay rate, up to 10% for the heaviest atoms, is observed due to the combination of these two effects. In the systematic analysis, we also include capture fractions for the first few dominant partial captures. Our precise model enables a close examination of low Q-value double electron capture in 152Gd, 164Er, and 242Cm, where partial KK captures are energetically forbidden. Finally, with the updated phase-space values, we recalculate the effective nuclear matrix elements and compare their spread with those associated with 2&nu;&beta;&minus;&beta;&minus; decay.

]]>Universe doi: 10.3390/universe10020097

Authors: Sándor Frey Judit Fogasy Krisztina Perger Kateryna Kulish Petra Benke Dávid Koller Krisztina Éva Gabányi

The prominent radio quasar PKS 2215+020 (J2217+0220) was once labelled as a new laboratory for core&ndash;jet physics at redshift z=3.572 because of its exceptionally extended jet structure traceable with very long baseline interferometric (VLBI) observations up to a &sim;600 pc projected distance from the compact core and a hint of an arcsec-scale radio and an X-ray jet. While the presence of an X-ray jet could not be confirmed later, this active galactic nucleus is still unique at high redshift with its long VLBI jet. Here, we analyse archival multi-epoch VLBI imaging data at five frequency bands from 1.7 to 15.4 GHz covering a period of more than 25 years from 1995 to 2020. We constrain apparent proper motions of jet components in PKS 2215+020 for the first time. Brightness distribution modeling at 8 GHz reveals a nearly 0.02 mas yr&minus;1 proper motion (moderately superluminal with apparently two times the speed of light), and provides &delta;=11.5 for the Doppler-boosting factor in the inner relativistic jet that is inclined within 2&#8728; to the line of sight and has a &Gamma;=6 bulk Lorentz factor. These values qualify PKS 2215+020 as a blazar, with rather typical jet properties in a small sample of only about 20 objects at z&gt;3.5 that have similar measurements to date. According to the 2-GHz VLBI data, the diffuse and extended outer emission feature at &sim;60 mas from the core, probably a place where the jet interacts with and decelerated by the ambient galactic medium, is consistent with being stationary, albeit slow motion cannot be excluded based on the presently available data.

]]>Universe doi: 10.3390/universe10020096

Authors: Xiao-Bo Zou Soumya D. Mohanty Hong-Gang Luo Yu-Xiao Liu

Swarm intelligence (SI) methods are nature-inspired metaheuristics for global optimization that exploit a coordinated stochastic search strategy by a group of agents. Particle swarm optimization (PSO) is an established SI method that has been applied successfully to the optimization of rugged high-dimensional likelihood functions, a problem that represents the main bottleneck across a variety of gravitational wave (GW) data analysis challenges. We present results from the first application of PSO to one of the most difficult of these challenges, namely the search for the Extreme Mass Ratio Inspiral (EMRI) in data from future spaceborne GW detectors such as LISA, Taiji, or Tianqin. We use the standard Generalized Likelihood Ratio Test formalism, with the minimal use of restrictive approximations, to search 6 months of simulated LISA data and quantify the search depth, signal-to-noise ratio (SNR), and breadth, within the ranges of the EMRI parameters, that PSO can handle. Our results demonstrate that a PSO-based EMRI search is successful for a search region ranging over &#8819;10&sigma; for the majority of parameters and &#8819;200&sigma; for one, with &sigma; being the SNR-dependent Cramer&ndash;Rao lower bound on the parameter estimation error and 30&le;SNR&le;50. This is in the vicinity of the search ranges that the current hierarchical schemes can identify. Directions for future improvement, including computational bottlenecks to be overcome, are identified.

]]>Universe doi: 10.3390/universe10020095

Authors: Colin MacLaurin Fabio Costa Timothy C. Ralph

We investigate timelike and null geodesics within the rotating &ldquo;time machine&rdquo; spacetime proposed by Ralph, T.C.; et al. Phys. Rev. D&nbsp;2020, 102, 124013. This is a rotating analogue of Alcubierre&rsquo;s warp drive spacetime. We obtain geodesics that begin and end in the surrounding flat space region, yet achieve time travel relative to static observers there. This is a global property, as the geodesics remain locally future-pointing, as well as timelike or null.

]]>Universe doi: 10.3390/universe10020093

Authors: Horst Lenske Jessica Bellone Maria Colonna Danilo Gambacurta José-Antonio Lay

The role of initial state (ISI) and final state (FSI) ion&ndash;ion interactions in heavy-ion double-charge-exchange (DCE) reactions A(Z,N)&rarr;A(Z&plusmn;2,N&#8723;2) are studied for double single-charge-exchange (DSCE) reactions given by sequential actions of the isovector nucleon&ndash;nucleon (NN) T-matrix. In momentum representation, the second-order DSCE reaction amplitude is shown to be given in factorized form by projectile and target nuclear matrix elements and a reaction kernel containing ISI and FSI. Expanding the intermediate propagator in a Taylor series with respect to auxiliary energy allows us to perform the summation in the leading-order term over intermediate nuclear states in closure approximation. The nuclear matrix element attains a form given by the products of two-body interactions directly exciting the n2p&minus;2 and p2n&minus;2 DCE transitions in the projectile and the target nucleus, respectively. A surprising result is that the intermediate propagation induces correlations between the transition vertices, showing that DSCE reactions are a two-nucleon process that resembles a system of interacting spin&ndash;isospin dipoles. Transformation of the DSCE NN T-matrix interactions from the reaction theoretical t-channel form to the s-channel operator structure required for spectroscopic purposes is elaborated in detail, showing that, in general, a rich spectrum of spin scalar, spin vector and higher-rank spin tensor multipole transitions will contribute to a DSCE reaction. Similarities (and differences) to two-neutrino double-beta decay (DBD) are discussed. ISI/FSI distortion and absorption effects are illustrated in black sphere approximation and in an illustrative application to data.

]]>Universe doi: 10.3390/universe10020094

Authors: Stefano Vercellone

Although celestial sources emitting in the few tens of GeV up to a few TeV are being investigated by imaging atmospheric &#268;erenkov telescope arrays such as H.E.S.S., MAGIC, and VERITAS, at higher energies, up to PeV, more suitable instrumentation is required to detect ultra-high-energy photons, such as extensive air shower arrays, as HAWC, LHAASO, Tibet AS-&gamma;. The Italian National Institute for Astrophysics has recently become the leader of an international project, the ASTRI Mini-Array, with the aim of installing and operating an array of nine dual-mirror &#268;erenkov telescopes at the Observatorio del Teide in Spain starting in 2025. The ASTRI Mini-Array is expected to span a wide range of energies (1&ndash;200 TeV), with a large field of view (about 10 degrees) and an angular and energy resolution of &sim;3 arcmin and &sim;10 %, respectively. The first four years of operations will be dedicated to the exploitation of Core Science, with a small and selected number of pointings with the goal of addressing some of the fundamental questions on the origin of cosmic rays, cosmology, and fundamental physics, the time-domain astrophysics and non &gamma;-ray studies (e.g., stellar intensity interferometry and direct measurements of cosmic rays). Subsequently, four more years will be dedicated to Observatory Science, open to the scientific community through the submission of observational proposals selected on a competitive basis. In this paper, I will review the Core Science topics and provide examples of possible Observatory Science cases, taking into account the synergies with current and upcoming observational facilities.

]]>Universe doi: 10.3390/universe10020092

Authors: Júlio C. Fabris Felipe T. Falciano Luiz F. Guimarães Nelson Pinto-Neto

After a century of cosmological observations, we have a solid standard model of cosmology. However, from a theoretical viewpoint, it is a compelling question if the cosmological data inevitably require an expanding universe independently of the theoretical framework. The possibility of obtaining a viable cosmological model with a constant scale-factor is discussed in the context of the Brans&ndash;Dicke class of scalar&ndash;tensor theories. It is shown that a flat spatial section requires the presence of a stiff matter fluid. However, some kinematical properties of the standard cosmological model can be reproduced. A realistic scenario may require a more complex class of scalar&ndash;tensor theories.

]]>Universe doi: 10.3390/universe10020091

Authors: Jaume de de Haro

Einstein presented the Hole Argument against General Covariance, understood as invariance with respect to a change in coordinates, as a consequence of his initial failure to obtain covariant equations that, in the weak static limit, contain Newton&rsquo;s law. Fortunately, about two years later, Einstein returned to General Covariance, and found these famous equations of gravity. However, the rejection of his Hole Argument carries a totally different vision of space-time. Its substantivalism notion, which is an essential ingredient in Newtonian theory and also in his special theory of relativity, has to be replaced, following Descartes and Leibniz&rsquo;s relationalism, by a set of &ldquo;point-coincidences&rdquo;.

]]>Universe doi: 10.3390/universe10020090

Authors: Costantino Sigismondi Paolo De Vincenzi

Solar and lunar eclipses are indeed the first astronomical phenomena which have been recorded since very early antiquity. Their periodicities gave birth to the first luni-solar calendars based on the Methonic cycle since the sixth century before Christ. The Saros cycle of 18.03 years is due to the Chaldean astronomical observations. Their eclipses&rsquo; observations reported by Ptolemy in the Almagest (Alexandria of Egypt, about 150 a.C.) enabled modern astronomers to recognize the irregular rotation rate of the Earth. The Earth&rsquo;s rotation is some hours in delay after the last three millenia if we use the present rotation to simulate the 721 b.C. total eclipse in Babylon. This is one of the most important issues in modern celestial mechanics, along with the Earth&rsquo;s axis nutation of 18 yr (discovered in 1737), precession of 25.7 Kyr (discovered by Ipparchus around 150 b.C.) and obliquity of 42 Kyr motions (discovered by Arabic astronomers and assessed from the Middle Ages to the modern era, IX to XVIII centuries). Newtonian and Einstenian gravitational theories explain fully these tiny motions, along with the Lense&ndash;Thirring gravitodynamic effect, which required great experimental accuracy. The most accurate lunar and solar theories, or their motion in analytical or numerical form, allow us to predict&mdash;along with the lunar limb profile recovered by a Japanese lunar orbiter&mdash;the appearance of total, annular solar eclipses or lunar occultations for a given place on Earth. The observation of these events, with precise timing, may permit us to verify the sphericity of the solar profile and its variability. The variation of the solar diameter on a global scale was claimed firstly by Angelo Secchi in the 1860s and more recently by Jack Eddy in 1978. In both cases, long and accurate observational campaigns started in Rome (1877&ndash;1937) and Greenwich Observatories, as well as at Yale University and the NASA and US Naval Observatory (1979&ndash;2011) with eclipses and balloon-borne heliometric observations. The IOTA/ES and US sections as well as the ICRA continued the eclipse campaigns. The global variations of the solar diameter over a decadal timescale, and at the millarcsecond level, may reflect some variation in solar energy output, which may explain some past climatic variations (such as the Aller&oslash;d and Dryas periods in Pleistocene), involving the outer layers of the Sun. &ldquo;An eclipse never comes alone&rdquo;; in the eclipse season, lasting about one month, we can have also lunar eclipses. Including the penumbral lunar eclipses, the probability of occurrence is equi-distributed amongst lunar and solar eclipses, but while the lunar eclipses are visible for a whole hemisphere at once, the solar eclipses are not. The color of the umbral shadow on the Moon was known since antiquity, and Galileo (1632, Dialogo sopra i Massimi Sistemi del Mondo) shows clearly these phenomena from copper color to a totally dark, eclipsed full Moon. Three centuries later, Andr&eacute; Danjon was able to correlate that umbral color with the 11-year cycle of solar activity. The forthcoming American total solar eclipse of 8 April 2024 will be probably the eclipse with the largest mediatic impact of the history; we wish that also the scientific impulse toward solar physics and astronomy will be relevant, and the measure of the solar diameter with Baily&rsquo;s beads is indeed one of the topics significantly related to the Sun&ndash;Earth connections.

]]>Universe doi: 10.3390/universe10020089

Authors: I. W. Bornhoeft R. G. Dias J. S. Engle

We introduce a notion of residual diffeomorphism covariance in quantum Kantowski&ndash;Sachs (KS) describing the interior of a Schwarzschild black hole. We solve for the family of Hamiltonian constraint operators satisfying the associated covariance condition, as well as parity invariance, preservation of the Bohr Hilbert space of the Loop Quantum KS and a correct (na&iuml;ve) classical limit. We further explore the imposition of minimality for the number of terms and compare the solution with those of other Hamiltonian constraints proposed for the Loop Quantum KS in the literature. In particular, we discuss a lapse that was recently commonly chosen due to the resulting decoupling of the evolution of the two degrees of freedom and the exact solubility of the model. We show that such a choice of lapse can indeed be quantized as an operator that is densely defined on the Bohr Hilbert space and that any such operator must include an infinite number of shift operators.

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