Universe

12 pages, 445 KiB

Open AccessArticle

by Bijan Saha

Universe 2023, 9(5), 243; https://doi.org/10.3390/universe9050243 - 22 May 2023

Cited by 1 | Viewed by 873

Within the scope of a Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model we study the role of a nonlinear spinor field in the evolution of the universe. In doing so, we exploit the FLRW models given in both Cartesian and spherical coordinates. It is found that [...] Read more.

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

(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)

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20 pages, 1107 KiB

Open AccessReview

Measurements of the Cross-Section for the \({{\rm t}{\bar{\rm t}}}\) Heavy-Flavor Production at the LHC

by Jorgen D’Hondt and Tae Jeong Kim

Universe 2023, 9(5), 242; https://doi.org/10.3390/universe9050242 - 21 May 2023

Viewed by 1088

Abstract

At the LHC, the process of a Higgs boson decaying into bottom or charm quarks produced in association with a pair of top quarks,

t \bar{t} H

, allows for an empirical exploration of the heavy-flavor quark Yukawa couplings to the Higgs [...] Read more.

At the LHC, the process of a Higgs boson decaying into bottom or charm quarks produced in association with a pair of top quarks,

t \bar{t} H

, allows for an empirical exploration of the heavy-flavor quark Yukawa couplings to the Higgs boson. Accordingly, the cross-sections for the

t \bar{t}

+ heavy-flavor production without the appearance of the Higgs boson have been measured at the LHC in various phase spaces using data samples collected in pp collisions at

\sqrt{s}

= 7, 8 and 13 TeV with the ATLAS and CMS experiments. Flavor ratios of cross-sections of

t \bar{t}

+ heavy-flavors to

t \bar{t}

+ additional jets processes are also measured. In this paper, the measured cross-sections and ratios are reviewed and the prospects with more data are presented. Full article

(This article belongs to the Special Issue Top Quark at the New Physics Frontier)

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24 pages, 492 KiB

Open AccessArticle

Bosonic Casimir Effect in an Aether-like Lorentz-Violating Scenario with Higher Order Derivatives

by Robson A. Dantas, Herondy F. Santana Mota and Eugênio R. Bezerra de Mello

Universe 2023, 9(5), 241; https://doi.org/10.3390/universe9050241 - 20 May 2023

Cited by 3 | Viewed by 715

Abstract

In this paper, we investigate the bosonic Casimir effect in a Lorentz-violating symmetry scenario. The theoretical model adopted consists of a real massive scalar quantum field confined in a region between two large parallel plates, having its dynamics governed by a modified Klein–Gordon [...] Read more.

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

(This article belongs to the Special Issue Quantum Field Theory)

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21 pages, 680 KiB

Open AccessArticle

Weak Neutrino (Antineutrino) Charged-Current Responses and Scaling for Nuclear Matter in the Relativistic Mean Field

by Sara Cruz-Barrios, Guillermo D. Megias and Juan A. Caballero

Universe 2023, 9(5), 240; https://doi.org/10.3390/universe9050240 - 19 May 2023

Viewed by 737

Abstract

A systematic analysis of the weak responses for charged-current quasielastic neutrino-nucleus reactions is presented within the scheme of a fully relativistic microscopic model considering momentum-dependent scalar and vector mean field potentials in both the initial and final nucleon states. The responses obtained are [...] Read more.

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

(This article belongs to the Special Issue Many Body Theory)

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30 pages, 4164 KiB

Open AccessArticle

Analysis of Resonant Periodic Orbits in the Framework of the Perturbed Restricted Three Bodies Problem

by Bhavika M. Patel, Niraj M. Pathak and Elbaz I. Abouelmagd

Universe 2023, 9(5), 239; https://doi.org/10.3390/universe9050239 - 18 May 2023

Cited by 2 | Viewed by 749

Abstract

In this work, the perturbed equations of motion of the infinitesimal body are constructed in the framework of the circular restricted three-body problem when the main two bodies are oblate and radiating. Under the perturbations effects of the oblateness and the radiation pressure [...] Read more.

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

(This article belongs to the Special Issue Testing General Relativity from the Solar System, Black Holes to Cosmology)

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9 pages, 276 KiB

Open AccessArticle

Nontrivial Topology Dynamical Corrections and the Magnetic Monopole-like Effect in Minkowski Spacetime

by Julio Marny Hoff da Silva and Rogerio Teixeira Cavalcanti

Universe 2023, 9(5), 238; https://doi.org/10.3390/universe9050238 - 18 May 2023

Viewed by 671

Abstract

We investigate two physical systems within a spacetime region affected by the nontrivial topology. The set-up for our analysis is a Minkowski metric perturbed by elements reflecting the topological nontriviality. These elements arise when exploring Cartan’s spinorial approach along with the exotic spinors [...] Read more.

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

(This article belongs to the Section Mathematical Physics)

13 pages, 1455 KiB

Open AccessArticle

Cosmological Neutrino N-Body Simulations of Dark Matter Halo

by Yu Chen, Chang-Zhi Lu, Juan Li, Siqi Liu, Tong-Jie Zhang and Tingting Zhang

Universe 2023, 9(5), 237; https://doi.org/10.3390/universe9050237 - 18 May 2023

Viewed by 834

Abstract

The study of massive neutrinos and their interactions is a critical aspect of contemporary cosmology. Recent advances in parallel computation and high-performance computing provide new opportunities for accurately constraining Large-Scale Structures (LSS). In this paper, we introduce the TianNu cosmological N-body simulation during [...] Read more.

The study of massive neutrinos and their interactions is a critical aspect of contemporary cosmology. Recent advances in parallel computation and high-performance computing provide new opportunities for accurately constraining Large-Scale Structures (LSS). In this paper, we introduce the TianNu cosmological N-body simulation during the co-evolution of massive neutrino and cold dark matter components via the CUBEP

^{3}

M code running on the supercomputer Tianhe-2 and TianNu’s connected works. We start by analyzing

2.537 \times 10^{7}

dark halos from the scientific data of TianNu simulation, and compare their angular momentum with the matched halos from neutrino-free TianZero, revealing a dependence of angular momentum modulus on neutrino injection at scales below 50 Mpc and around 10 Mpc. Full article

(This article belongs to the Section Cosmology)

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67 pages, 2758 KiB

Open AccessReview

Sp(2N) Lattice Gauge Theories and Extensions of the Standard Model of Particle Physics

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

Universe 2023, 9(5), 236; https://doi.org/10.3390/universe9050236 - 17 May 2023

Cited by 7 | Viewed by 1339

Abstract

We review the current status of the long-term programme of numerical investigation of

S p (2 N)

gauge theories with and without fermionic matter content. We start by introducing the phenomenological as well as theoretical motivations for this research programme, which [...] Read more.

We review the current status of the long-term programme of numerical investigation of

S p (2 N)

gauge theories with and without fermionic matter content. We start by introducing the phenomenological as well as theoretical motivations for this research programme, which are related to composite Higgs models, models of partial top compositeness, dark matter models, and in general to the physics of strongly coupled theories and their approach to the large-N limit. We summarise the results of lattice studies conducted so far in the

S p (2 N)

Yang–Mills theories, measuring the string tension, the mass spectrum of glueballs and the topological susceptibility, and discuss their large-N extrapolation. We then focus our discussion on

S p (4)

, and summarise the numerical measurements of mass and decay constant of mesons in the theories with fermion matter in either the fundamental or the antisymmetric representation, first in the quenched approximation, and then with dynamical fermions. We finally discuss the case of dynamical fermions in mixed representations, and exotic composite fermion states such as the chimera baryons. We conclude by sketching the future stages of the programme. We also describe our approach to open access. Full article

(This article belongs to the Special Issue Numerical Studies of Strongly Coupled Gauge Theories (SCGTs) in the Search of New Physics)

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20 pages, 2428 KiB

Open AccessArticle

Simulations on Synchrotron Radiation Intensity and Rotation Measure of Relativistic Magnetized Jet PKS 1502+106

by Che-Jui Chang and Jean-Fu Kiang

Universe 2023, 9(5), 235; https://doi.org/10.3390/universe9050235 - 17 May 2023

Viewed by 988

Abstract

Strong γ-ray outbursts have been observed to emanate from PKS 1502+106, followed by highly variable fluxes in radio, visual, ultraviolet and X-ray bands. Numerical simulations have been conducted to relate the observations to potential theoretical models. The plasma attributes, such as mass [...] Read more.

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

(This article belongs to the Special Issue Black Holes and Relativistic Jets)

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12 pages, 300 KiB

Open AccessArticle

Derivation of Emergent Spacetime Metric, Gravitational Potential and Speed of Light in Superfluid Vacuum Theory

by Konstantin G. Zloshchastiev

Universe 2023, 9(5), 234; https://doi.org/10.3390/universe9050234 - 17 May 2023

Viewed by 730

Abstract

Within the frameworks of the logarithmic superfluid model of physical vacuum, we demonstrate the emergence of four-dimensional curved spacetime from the dynamics of quantum Bose liquid in three-dimensional Euclidean space. We derive the metric tensor of this spacetime and study its special cases [...] Read more.

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

(This article belongs to the Section Gravitation)

6 pages, 1450 KiB

Open AccessCommunication

With Nanoplasmonics towards Fusion

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

Universe 2023, 9(5), 233; https://doi.org/10.3390/universe9050233 - 17 May 2023

Cited by 1 | Viewed by 1030

Abstract

A status report is presented about the Nanoplasmonic Laser Induced Fusion Experiment (NAPLIFE). The goal is to investigate and verify plasmonically enhanced phenomena on the surfaces of nanoantennas embedded in a polymer target at laser intensities up to a few times

10^{16}

[...] Read more.

A status report is presented about the Nanoplasmonic Laser Induced Fusion Experiment (NAPLIFE). The goal is to investigate and verify plasmonically enhanced phenomena on the surfaces of nanoantennas embedded in a polymer target at laser intensities up to a few times

10^{16}

W/cm

^{2}

and pulse durations of 40–120 fs. The first results on enhanced crater formation for Au-doped polymer targets are shown, and SERS signals typical for

{CD}_{2}

and

ND

bound vibrations are cited. Trials to detect

D / H

ratio by means of LIBS measurments are reported. Plasmonics has the potential to work at these intensities, enhancing the energy and deuterium production, due to thus far unknown mechanisms. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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27 pages, 407 KiB

Open AccessArticle

Teleparallel Minkowski Spacetime with Perturbative Approach for Teleparallel Gravity on a Proper Frame

by Alexandre Landry and Robert J. van den Hoogen

Universe 2023, 9(5), 232; https://doi.org/10.3390/universe9050232 - 15 May 2023

Cited by 1 | Viewed by 778

Abstract

A complete perturbation theory suitable for teleparallel gravity is developed. The proposed perturbation scheme takes into account perturbations of the coframe, the metric, and the spin-connection, while ensuring that the resulting perturbed system continues to describe a teleparallel gravity situation. The resulting perturbation [...] Read more.

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

f (T)

teleparallel gravity and discuss the stability of the teleparallel Minkowski geometry within

f (T)

teleparallel gravity. Full article

(This article belongs to the Special Issue Mathematical Cosmology)

13 pages, 293 KiB

Open AccessArticle

Functional Integrals in Geometric Approach to Quantum Theory

by Igor Frolov and Albert Schwarz

Universe 2023, 9(5), 231; https://doi.org/10.3390/universe9050231 - 15 May 2023

Viewed by 668

Abstract

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

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

(This article belongs to the Special Issue Universe: Feature Papers 2023—Field Theory)

12 pages, 1106 KiB

Open AccessArticle

Aurora Classification in All-Sky Images via CNN–Transformer

by Jian Lian, Tianyu Liu and Yanan Zhou

Universe 2023, 9(5), 230; https://doi.org/10.3390/universe9050230 - 15 May 2023

Cited by 4 | Viewed by 1367

Abstract

An aurora is a unique geophysical phenomenon with polar characteristics that can be directly observed with the naked eye. It is the most concentrated manifestation of solar–terrestrial physical processes (especially magnetospheric–ionospheric interactions) in polar regions and is also the best window for studying [...] Read more.

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

(This article belongs to the Special Issue Auroral Physics)

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16 pages, 8461 KiB

Open AccessArticle

Analysis of Pre-Earthquake Ionospheric Anomalies in the Japanese Region Based on DEMETER Satellite Data

by Jingming Lu, Yaogai Hu, Chunhua Jiang, Zhengyu Zhao, Yuannong Zhang and Zhengzheng Ma

Universe 2023, 9(5), 229; https://doi.org/10.3390/universe9050229 - 14 May 2023

Cited by 1 | Viewed by 1157

Abstract

The electron density (N_e), ion density (N_i), and electron temperature (T_e) statistics recorded by the DEMETER satellite payload ISL (Instrument Sonde de Langmuir) were used to study the disturbance characteristics of the ionosphere before [...] Read more.

The electron density (N_e), ion density (N_i), and electron temperature (T_e) statistics recorded by the DEMETER satellite payload ISL (Instrument Sonde de Langmuir) were used to study the disturbance characteristics of the ionosphere before solid earthquakes of magnitude 6 or higher in Japan during the summer of

2005 - 2009

, to provide more information and methods for the coupling mechanism and short-range earthquake prediction. In this paper, the region of

\pm 10 °

of the epicenter is divided into

1 ° \times 1 °

pixels, and the background field of each parameter is constructed using data without earthquakes and relatively calm space weather. We also define a measure of the perturbation intensity of ionospheric parameters relative to the background field during the occurrence of earthquakes. The analysis results of the four Japanese earthquakes from space and time show an excellent synchronization in the time and area of the anomalies in ionospheric parameters of the four cases. All four instances showed N_e abnormalities, and three showed N_i and T_e anomalies, in which

N_{e}

and N_i increased or decreased abnormally, while T_e increased abnormally every time, and the anomalies mainly occurred about 9–12 days before the earthquake. This paper eliminates the influence of solar, geomagnetic, and satellite data defects on the experimental results as much as possible in data screening and method selection. The results partially agree with the conclusions reported in the existing literature, and the obtained anomalies are somewhat related to the ionospheric precursors of earthquakes. Full article

(This article belongs to the Section Space Science)

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12 pages, 461 KiB

Open AccessArticle

The Hawking Radiation in Massive Gravity: Path Integral and the Bogoliubov Method

by Ivan Arraut, Carlos Segovia and Wilson Rosado

Universe 2023, 9(5), 228; https://doi.org/10.3390/universe9050228 - 13 May 2023

Viewed by 698

Abstract

We prove the consistency of the different approaches for deriving the black hole radiation for the spherically symmetric case inside the theory of Massive Gravity. By comparing the results obtained by using the Bogoliubov transformations with those obtained by using the Path Integral [...] Read more.

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

(This article belongs to the Section Gravitation)

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24 pages, 6125 KiB

Open AccessArticle

Magnetic Activity of Different Types of Variable Stars Observed by TESS Mission

by Ming Zhong, Liyun Zhang, Zilu Yang and Tianhao Su

Universe 2023, 9(5), 227; https://doi.org/10.3390/universe9050227 - 13 May 2023

Cited by 1 | Viewed by 826

Abstract

The investigation of the magnetic activity of different types of variable stars holds significant implications for our understanding of the physical processes and evolution of stars. This study’s International Variable Star Index (VSX) variable star catalog was cross-matched with Transiting Exoplanet Survey Satellite [...] Read more.

The investigation of the magnetic activity of different types of variable stars holds significant implications for our understanding of the physical processes and evolution of stars. This study’s International Variable Star Index (VSX) variable star catalog was cross-matched with Transiting Exoplanet Survey Satellite (TESS) data, resulting in 26,276 labeled targets from 76,187 light curves. A total of 25,327 stellar flare events were detected, including 245 eclipsing binaries, 2324 rotating stars, 111 pulsating stars, and 629 eruptive stars. The results showed that flares from eclipsing binaries, rotating stars, eruptive stars, and pulsating stars have durations such that 90% are less than 2 h, and 91% of their amplitudes are less than 0.3. Flare events mainly occurred in the temperature range of 2000 K to 3000 K. The power-law indices of different types of variable stars were

1.72 \pm 0.025

(eclipsing binaries),

1.82 \pm 0.062

(rotating stars),

1.80 \pm 0.0116

(eruptive stars), and

1.73 \pm 0.060

(pulsating stars). Among them, the flare energy of pulsating stars is more concentrated in the high-energy range. In all samples, flare energies were distributed from

3.99 \times 10^{31}

erg to

6.18 \times 10^{38}

erg. The LAMOST DR9 low-resolution spectral survey has provided H

α

equivalent widths for 398 variable stars. By utilizing these H

α

equivalent widths, we have determined the stellar activity of the variable stars and confirmed a positive correlation between the flare energy and H

α

equivalent width. Full article

(This article belongs to the Section Stellar Astronomy)

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19 pages, 528 KiB

Open AccessArticle

Modelling Neutron-Star Ocean Dynamics

by Fabian Gittins, Thomas Celora, Aru Beri and Nils Andersson

Universe 2023, 9(5), 226; https://doi.org/10.3390/universe9050226 - 12 May 2023

Cited by 1 | Viewed by 808

Abstract

We revisit the calculation of mode oscillations in the ocean of a rotating neutron star, which may be excited during thermonuclear X-ray bursts. Our present theoretical understanding of ocean modes relies heavily on the traditional approximation commonly employed in geophysics. The approximation elegantly [...] Read more.

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

(This article belongs to the Section Compact Objects)

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21 pages, 3926 KiB

Open AccessArticle

Probing the Lorentz Invariance Violation via Gravitational Lensing and Analytical Eigenmodes of Perturbed Slowly Rotating Bumblebee Black Holes

by Mert Mangut, Huriye Gürsel, Sara Kanzi and İzzet Sakallı

Universe 2023, 9(5), 225; https://doi.org/10.3390/universe9050225 - 12 May 2023

Cited by 12 | Viewed by 969

Abstract

The ability of bumblebee gravity models to explain dark energy, which is the phenomenon responsible for the universe’s observed accelerated expansion, is one of their most significant applications. An effect that causes faster expansion can be linked to how much the Lorentz symmetry [...] Read more.

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

(This article belongs to the Special Issue Advances in Gravitational Lensing and Gravitational Waves Research)

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17 pages, 950 KiB

Open AccessArticle

Traveling Wave Solutions and Conservation Laws of a Generalized Chaffee–Infante Equation in (1+3) Dimensions

by Motshidisi Charity Sebogodi, Ben Muatjetjeja and Abdullahi Rashid Adem

Universe 2023, 9(5), 224; https://doi.org/10.3390/universe9050224 - 08 May 2023

Cited by 4 | Viewed by 926

Abstract

This paper aims to analyze a generalized Chaffee–Infante equation with power-law nonlinearity in (1+3) dimensions. Ansatz methods are utilized to provide topological and non-topological soliton solutions. Soliton solutions to nonlinear evolution equations have several practical applications, including plasma physics and the diffusion process, [...] Read more.

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

(This article belongs to the Special Issue Mathematical Cosmology)

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17 pages, 349 KiB

Open AccessArticle

Killing Horizons and Surface Gravities for a Well-Behaved Three-Function Generalization of the Kerr Spacetime

by Joshua Baines and Matt Visser

Universe 2023, 9(5), 223; https://doi.org/10.3390/universe9050223 - 08 May 2023

Cited by 6 | Viewed by 1312

Abstract

Thanks to the recent advent of the event horizon telescope (EHT), we now have the opportunity to test the physical ramifications of the strong-field near-horizon regime for astrophysical black holes. Herein, emphasizing the trade-off between tractability and generality, the authors discuss a particularly [...] Read more.

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

(This article belongs to the Collection Open Questions in Black Hole Physics)

25 pages, 473 KiB

Open AccessArticle

Octonion Internal Space Algebra for the Standard Model

by Ivan Todorov

Universe 2023, 9(5), 222; https://doi.org/10.3390/universe9050222 - 06 May 2023

Cited by 4 | Viewed by 926

Abstract

This paper surveys recent progress in our search for an appropriate internal space algebra for the standard model (SM) of particle physics. After a brief review of the existing approaches, we start with the Clifford algebras involving operators of left multiplication by octonions. [...] Read more.

This paper surveys recent progress in our search for an appropriate internal space algebra for the standard model (SM) of particle physics. After a brief review of the existing approaches, we start with the Clifford algebras involving operators of left multiplication by octonions. A central role is played by a distinguished complex structure that implements the splitting of the octonions

O = C \oplus C^{3}

, which reflect the lepton-quark symmetry. Such a complex structure on the 32-dimensional space

S

of

C ℓ_{10}

Majorana spinors is generated by the

C ℓ_{6} (\subset C ℓ_{10})

volume form,

ω_{6} = γ_{1} \dots γ_{6}

, and is left invariant by the Pati–Salam subgroup of

S p i n (10)

,

G_{PS} = S p i n (4) \times S p i n (6) / Z_{2}

. While the

S p i n (10)

invariant volume form

ω_{10} = γ_{1} \dots γ_{10}

of

C ℓ_{10}

is known to split

S

on a complex basis into left and right chiral (semi)spinors,

P = \frac{1}{2} (1 - i ω_{6})

is interpreted as the projector on the 16-dimensional particle subspace (which annihilates the antiparticles).The standard model gauge group appears as the subgroup of

G_{PS}

that preserves the sterile neutrino (which is identified with the Fock vacuum). The

Z_{2}

-graded internal space algebra

A

is then included in the projected tensor product

A \subset P C ℓ_{10} P = C ℓ_{4} \otimes C ℓ_{6}^{0}

. The Higgs field appears as the scalar term of a superconnection, an element of the odd part

C ℓ_{4}^{1}

of the first factor. The fact that the projection of

C ℓ_{10}

only involves the even part

C ℓ_{6}^{0}

of the second factor guarantees that the color symmetry remains unbroken. As an application, we express the ratio

\frac{m_{H}}{m_{W}}

of the Higgs to the W boson masses in terms of the cosine of the theoretical Weinberg angle. Full article

(This article belongs to the Section Mathematical Physics)

14 pages, 705 KiB

Open AccessArticle

CMB Power Spectrum in the Emergent Universe with K-Essence

by Qihong Huang, Kaituo Zhang, He Huang, Bing Xu and Feiquan Tu

Universe 2023, 9(5), 221; https://doi.org/10.3390/universe9050221 - 06 May 2023

Cited by 3 | Viewed by 840

Abstract

The emergent universe provides a possible method to avoid the Big Bang singularity by considering that the universe stems from a stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in [...] Read more.

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

(This article belongs to the Special Issue Cosmic Microwave Background)

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11 pages, 490 KiB

Open AccessArticle

The Elasticity of the Neutron Star Mantle: The Improved Compressible Liquid Drop Model for Cylindrical Phases

by Nikita A. Zemlyakov and Andrey I. Chugunov

Universe 2023, 9(5), 220; https://doi.org/10.3390/universe9050220 - 04 May 2023

Cited by 1 | Viewed by 1113

Abstract

Neutron stars are the densest objects in the Universe. They have a microscopically homogeneous core and heterogeneous crust. In particular, there may be a specific layer inside neutron stars, the mantle, which consists of substantially non-spherical nuclei immersed in a background of relativistic [...] Read more.

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

(This article belongs to the Special Issue Advances in Magnetars)

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11 pages, 1711 KiB

Open AccessArticle

Coulomb Problem for Classical Spinning Particles

by Dmitry S. Kaparulin and Nikita A. Sinelnikov

Universe 2023, 9(5), 219; https://doi.org/10.3390/universe9050219 - 04 May 2023

Cited by 2 | Viewed by 1093

Abstract

We consider the motion of a weakly relativistic charged particle with an arbitrary spin in central potential

e / r

in terms of classical mechanics. We show that the spin–orbital interaction causes the precession of the plane of orbit around the vector of [...] Read more.

We consider the motion of a weakly relativistic charged particle with an arbitrary spin in central potential

e / r

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

(This article belongs to the Special Issue Elementary Particles in Astrophysics and Cosmology)

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18 pages, 2034 KiB

Open AccessArticle

A Swift Response to Newly Discovered, Nearby Transients

by Peter J. Brown, Macie Robertson, Yaswant Devarakonda, Emily Sarria, David Pooley and Maximilian D. Stritzinger

Universe 2023, 9(5), 218; https://doi.org/10.3390/universe9050218 - 03 May 2023

Cited by 1 | Viewed by 1181

Abstract

The Neil Gehrels Swift Observatory has proven to be an extraordinary supernova (SN) observatory. The clearest application of Swift’s unique strengths is obtaining very early UV and X-ray data of young SNe, which enables robust constraints on their progenitor systems. As part of [...] Read more.

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

(This article belongs to the Special Issue 18 Years of Science with the Neil Gehrels Swift Observatory's Ultra-Violet/Optical Telescope)

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10 pages, 312 KiB

Open AccessArticle

Particles of Negative and Zero Energy in Black Holes and Cosmological Models

by Andrey A. Grib and Yuri V. Pavlov

Universe 2023, 9(5), 217; https://doi.org/10.3390/universe9050217 - 01 May 2023

Viewed by 988

Abstract

Particles with negative energies are considered for three different cases: inside the horizon of a Schwarzschild black hole, Milne’s coordinates in flat Minkowski space–time (Milne’s universe using nonsynchronous coordinates) and in the cosmological Gödel model of the rotating universe. It is shown that, [...] Read more.

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

(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)

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15 pages, 5480 KiB

Open AccessArticle

The Casimir Effect between Parallel Plates Separated by Uniaxial Media: The Effects Due to the Orientation of the Optical Axis

by Gang Deng, Ye Xu, Ling Pei, Ni Hu and Hongjing Xu

Universe 2023, 9(5), 216; https://doi.org/10.3390/universe9050216 - 01 May 2023

Viewed by 938

Abstract

The Casimir force is calculated in the configuration of two parallel plates separated by an anisotropic media. The result exhibits a dependence on the orientation of the optical axis of the intervening media. It is possible that the Casimir force switches its direction [...] Read more.

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

(This article belongs to the Section Field Theory)

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13 pages, 1969 KiB

Open AccessArticle

Quasi-Periodic Pulsations in an M-Class Solar Flare

by Jun Xu, Zongjun Ning, Dong Li and Fanpeng Shi

Universe 2023, 9(5), 215; https://doi.org/10.3390/universe9050215 - 30 Apr 2023

Cited by 1 | Viewed by 839

Abstract

We have studied the quasi-periodic pulsations (QPPs) of the M2.3 flare that occurred in the active region NOAA 12172 on 23 September 2014. Through the fast Fourier transform (FFT) method, we decompose the flare light curves into fast- and slowly-varying components, and the [...] Read more.

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

(This article belongs to the Special Issue Solar Radio Emissions)

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16 pages, 5757 KiB

Open AccessArticle

Explaining the Muon g − 2 Anomaly in Deflected AMSB for NMSSM

by Lijun Jia, Zhuang Li and Fei Wang

Universe 2023, 9(5), 214; https://doi.org/10.3390/universe9050214 - 29 Apr 2023

Cited by 6 | Viewed by 1070

Abstract

We propose to embed the General NMSSM (Next-to-Minimal Supersymmetric Standard Model) into the deflected AMSB (Anomaly Mediated Supersymmetry Breaking) mechanism with Yukawa/gauge deflection contributions. After the integration of the heavy messenger fields, the analytical expressions of the relevant soft SUSY breaking spectrum for [...] Read more.

We propose to embed the General NMSSM (Next-to-Minimal Supersymmetric Standard Model) into the deflected AMSB (Anomaly Mediated Supersymmetry Breaking) mechanism with Yukawa/gauge deflection contributions. After the integration of the heavy messenger fields, the analytical expressions of the relevant soft SUSY breaking spectrum for General NMSSM at the messenger scale can be calculated. We find that successful EWSB (Electroweak Symmetry Breaking) and realistic low energy NMSSM spectrum can be obtained in some parameter regions. In addition, we find that the muon

g - 2

anomaly and electron

g - 2

anomaly (for positive central value electron

g - 2

experimental data) can be jointly explained to

1 σ

and

2 σ

range, respectively. The

Z_{3}

invariant NMSSM, which corresponds to

ξ_{F} = 0

in our case, can also jointly explain the muon and electron anomaly to

1 σ

and

2 σ

range, respectively. Full article

(This article belongs to the Special Issue Origin of the Flavor Structure in the Standard Model and Beyond)

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