Universe

17 pages, 723 KiB

Open AccessReview

Flavour-Changing Neutral Scalar Interactions of the Top Quark

by Nuno Filipe Castro and Kirill Skovpen

Universe 2022, 8(11), 609; https://doi.org/10.3390/universe8110609 - 21 Nov 2022

Cited by 7 | Viewed by 2164

A study of the top-quark interactions via flavour-changing neutral current (FCNC) processes provides an intriguing connection between the heaviest elementary particle of the standard model (SM) of particle physics and the new scalar bosons that are predicted in several notable SM extensions. The [...] Read more.

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

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

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9 pages, 318 KiB

Open AccessArticle

Impact of Lorentz Violation Models on Exoplanets’ Dynamics

by Antonio Gallerati, Matteo Luca Ruggiero and Lorenzo Iorio

Universe 2022, 8(11), 608; https://doi.org/10.3390/universe8110608 - 18 Nov 2022

Cited by 2 | Viewed by 1410

Abstract

Many exoplanets have been detected by the radial velocity method, according to which the motion of a binary system around its center of mass can produce a periodical variation of the Doppler effect of the light emitted by the host star. These variations [...] Read more.

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

(This article belongs to the Section Gravitation)

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26 pages, 6180 KiB

Open AccessReview

Active Galactic Nuclei as Potential Sources of Ultra-High Energy Cosmic Rays

by Frank M. Rieger

Universe 2022, 8(11), 607; https://doi.org/10.3390/universe8110607 - 17 Nov 2022

Cited by 15 | Viewed by 2593

Abstract

Active Galactic Nuclei (AGNs) and their relativistic jets belong to the most promising class of ultra-high-energy cosmic ray (UHECR) accelerators. This compact review summarises basic experimental findings by recent instruments, and discusses possible interpretations and astrophysical constraints on source energetics. Particular attention is [...] Read more.

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

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

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3 pages, 165 KiB

Open AccessEditorial

Editorial for the Special Issue “Neutrinoless Double Beta Decay”

by Fabio Bellini and Claudia Tomei

Universe 2022, 8(11), 606; https://doi.org/10.3390/universe8110606 - 17 Nov 2022

Viewed by 1252

Abstract

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

(This article belongs to the Special Issue Neutrinoless Double Beta Decay)

9 pages, 970 KiB

Open AccessArticle

N-S Asymmetry and Solar Cycle Distribution of Superactive Regions from 1976 to 2017

by Ming-Xian Zhao, Gui-Ming Le and Yong-Hua Liu

Universe 2022, 8(11), 605; https://doi.org/10.3390/universe8110605 - 17 Nov 2022

Cited by 2 | Viewed by 1366

Abstract

There were 51 superactive regions (SARs) during solar cycles (SCs) 21–24. We divided the SARs into SARs₁, which produced extreme space weather events including ≥X5.0 flares, ground level events (GLEs), and super geomagnetic storms (SGSs, Dst < −250 nT), and SARs [...] Read more.

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

(This article belongs to the Special Issue Small-Scale Eruptions on the Sun)

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10 pages, 306 KiB

Open AccessArticle

Connections between the Shadow Radius and the Quasinormal Modes of Kerr-Sen Black Hole

by Xianglong Wu and Xiangdong Zhang

Universe 2022, 8(11), 604; https://doi.org/10.3390/universe8110604 - 17 Nov 2022

Cited by 5 | Viewed by 1230

Abstract

The correspondence between the shadow radius and the real part of the quasinormal modes (QNMs) of a Kerr–Sen black hole is studied. By using the equation of the shadow radius of Kerr–Sen black hole and the angular separation constant of the QNMs, the [...] Read more.

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

(This article belongs to the Section Cosmology)

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25 pages, 472 KiB

Open AccessArticle

Effective Field Theory Description of Horizon-Fluid Determines the Scrambling Time

by Swastik Bhattacharya and S. Shankaranarayanan

Universe 2022, 8(11), 603; https://doi.org/10.3390/universe8110603 - 17 Nov 2022

Viewed by 1354

Abstract

Black hole horizons interact with external fields when matter or energy falls through them. Such non-stationary black hole horizons can be described using viscous fluid equations. This work attempts to describe this process using effective field theory methods. Such a description can provide [...] Read more.

Black hole horizons interact with external fields when matter or energy falls through them. Such non-stationary black hole horizons can be described using viscous fluid equations. This work attempts to describe this process using effective field theory methods. Such a description can provide important insights beyond classical black hole physics. In this work, we construct a low-energy effective field theory description for the horizon-fluid of a 4-dimensional, asymptotically flat, Einstein black hole. The effective field theory of the dynamical horizon has two ingredients: degrees of freedom involved in the interaction with external fields and symmetry. The dual requirements of incorporating near-horizon symmetries (

S 1

diffeomorphism) and possessing length scales due to external perturbations are naturally satisfied if the theory on the non-stationary black hole horizon is a deformed Conformal Field Theory (CFT). For the homogeneous external perturbations, at the lowest order, this leads to a

(2 + 1)

-dimensional massive scalar field where the mass is related to the extent of the deformation of the CFT. We determine the mass by obtaining the correlation function corresponding to the effective field and relating it to the bulk viscosity of the horizon-fluid. Additionally, we show that the coefficient of bulk viscosity of the horizon-fluid determines the time required for black holes to scramble. Furthermore, we argue that matter-field modes with energy less than

m_{eff}

falling into the horizon thermalize more slowly. Finally, we construct a microscopic toy model for the horizon-fluid that reduces to the effective field theory with a single scalar degree of freedom. We then discuss the usefulness of the effective field model in understanding how information escapes from a black hole at late times. Full article

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

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14 pages, 5127 KiB

Open AccessArticle

Transient Flashes in Saturn’s UV Aurora: An Analysis of Hubble Space Telescope 2013–2017 Campaigns and Cassini Magnetic Field Measurements

by Tianshu Qin, Sarah V. Badman, Joe Kinrade and Alexander Bader

Universe 2022, 8(11), 602; https://doi.org/10.3390/universe8110602 - 17 Nov 2022

Viewed by 1721

Abstract

We examined Hubble Space Telescope images of Saturn’s northern UV aurora in 2013–2017, identified 29 short-lived flashes, and examined simultaneous magnetometer data collected by the Cassini orbiter. When observation cadence permitted, a flash lifetime of 4–17 min (subject to exposure time-related uncertainties), and [...] Read more.

We examined Hubble Space Telescope images of Saturn’s northern UV aurora in 2013–2017, identified 29 short-lived flashes, and examined simultaneous magnetometer data collected by the Cassini orbiter. When observation cadence permitted, a flash lifetime of 4–17 min (subject to exposure time-related uncertainties), and a 40–70 min recurrence period were found. An occurrence map shows a strong preference in both local time (14–19 LT) and latitude (75–85

^{°}

). These transient flashes are identified in both the presence and absence of Saturn’s main auroral oval, indicating the lack of dependence on the main emission power. The concurrent magnetic field pulsations generally form a sawtooth shape, and the local field strength experiences a change of 0.2 to 2.0 nT (depending on the distance of Cassini). The quasiperiodic pulsation events were all detected when the spacecraft was in the southern hemisphere with conjugate flashes in northern aurora, suggesting these events occur on closed field lines, and typically showing a sudden transition to a less lagging, more southward magnetic field configuration. We also found the ionospheric footprint of the spacecraft must be close to the region of flashes for magnetic field pulsations to be detected, implying a localised rather than global driving process. Full article

(This article belongs to the Special Issue Auroral Physics)

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16 pages, 347 KiB

Open AccessArticle

Density Matrix Formalism for Interacting Quantum Fields

by Christian Käding and Mario Pitschmann

Universe 2022, 8(11), 601; https://doi.org/10.3390/universe8110601 - 16 Nov 2022

Cited by 4 | Viewed by 1645

Abstract

We provide a description of interacting quantum fields in terms of density matrices for any occupation numbers in Fock space in a momentum basis. As a simple example, we focus on a real scalar field interacting with another real scalar field, and present [...] Read more.

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

(This article belongs to the Section Field Theory)

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6 pages, 214 KiB

Open AccessArticle

Discretely Charged Dark Matter in Inflation Models Based on Holographic Space-Time

by Tom Banks and Willy Fischler

Universe 2022, 8(11), 600; https://doi.org/10.3390/universe8110600 - 14 Nov 2022

Cited by 7 | Viewed by 1574

Abstract

The holographic space-time (HST) model of inflation has a potential explanation for dark matter as tiny primordial black holes. Motivated by a recent paper of Barrau, we propose a version of this model where some of the inflationary black holes (IBHs), whose decay [...] Read more.

The holographic space-time (HST) model of inflation has a potential explanation for dark matter as tiny primordial black holes. Motivated by a recent paper of Barrau, we propose a version of this model where some of the inflationary black holes (IBHs), whose decay gives rise to the Hot Big Bang, carry the smallest value of a discrete symmetry charge. The fraction f of IBHs carrying this charge is difficult to estimate from first principles, but we determine it by requiring that the crossover between radiation and matter domination occurs at the correct temperature

T_{e q} \sim 1 eV = 10^{- 28} M_{P}

. The fraction is small,

f \sim 2 \times 10^{- 9}

, so we believe this gives an extremely plausible model of dark matter. Full article

(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy)

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13 pages, 483 KiB

Open AccessArticle

Weak Deflection Angle by Kalb–Ramond Traversable Wormhole in Plasma and Dark Matter Mediums

by Wajiha Javed, Hafsa Irshad, Reggie C. Pantig and Ali Övgün

Universe 2022, 8(11), 599; https://doi.org/10.3390/universe8110599 - 13 Nov 2022

Cited by 24 | Viewed by 1539

Abstract

This paper is devoted to computing the weak deflection angle for the Kalb–Ramond traversable wormhole solution in plasma and dark matter mediums by using the method of Gibbons and Werner. To acquire our results, we evaluate Gaussian optical curvature by utilizing the Gauss–Bonnet [...] Read more.

This paper is devoted to computing the weak deflection angle for the Kalb–Ramond traversable wormhole solution in plasma and dark matter mediums by using the method of Gibbons and Werner. To acquire our results, we evaluate Gaussian optical curvature by utilizing the Gauss–Bonnet theorem in the weak field limits. We also investigate the graphical influence of the deflection angle

\tilde{α}

with respect to the impact parameter

σ

and the minimal radius

r_{0}

in the plasma medium. Moreover, we derive the deflection angle by using a different method known as the Keeton and Petters method. We also examine that if we remove the effects of plasma and dark matter, the results become identical to that of the non-plasma case. Full article

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

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16 pages, 328 KiB

Open AccessArticle

Equivalence Principle in Classical and Quantum Gravity

by Nikola Paunković and Marko Vojinović

Universe 2022, 8(11), 598; https://doi.org/10.3390/universe8110598 - 12 Nov 2022

Cited by 5 | Viewed by 1949

Abstract

We give a general overview of various flavours of the equivalence principle in classical and quantum physics, with special emphasis on the so-called weak equivalence principle, and contrast its validity in mechanics versus field theory. We also discuss its generalisation to a theory [...] Read more.

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

(This article belongs to the Special Issue Quantum Gravity Phenomenology II)

13 pages, 317 KiB

Open AccessArticle

Thermal Casimir Effect in the Einstein Universe with a Spherical Boundary

by Herondy F. S. Mota, Celio R. Muniz and Valdir B. Bezerra

Universe 2022, 8(11), 597; https://doi.org/10.3390/universe8110597 - 12 Nov 2022

Cited by 4 | Viewed by 1216

Abstract

In the present paper, we investigate thermal fluctuation corrections to the vacuum energy at zero temperature of a conformally coupled massless scalar field, whose modes propagate in the Einstein universe with a spherical boundary, characterized by both Dirichlet and Neumann boundary conditions. Thus, [...] Read more.

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

(This article belongs to the Section High Energy Nuclear and Particle Physics)

18 pages, 1072 KiB

Open AccessArticle

The Barium Odd Isotope Fractions in Seven Ba Stars

by Fang Wen, Wenyuan Cui, Miao Tian, Xiaoxiao Zhang, Jianrong Shi and Bo Zhang

Universe 2022, 8(11), 596; https://doi.org/10.3390/universe8110596 - 12 Nov 2022

Viewed by 1270

Abstract

Based on the spectra with high resolution and a high signal-to-noise ratio, we investigate the enrichment history of the s-process element in seven barium (Ba) stars by measuring their Ba odd isotope fraction. It is found that the relative contributions of the s-process [...] Read more.

Based on the spectra with high resolution and a high signal-to-noise ratio, we investigate the enrichment history of the s-process element in seven barium (Ba) stars by measuring their Ba odd isotope fraction. It is found that the relative contributions of the s-process to their Ba abundance are

91.4 \pm 25.7 %

,

91.4 \pm 34.3 %

,

82.9 \pm 28.5 %

,

77.1 \pm 31.4 %

, and

71.4 \pm 37.1 %

for REJ 0702+129, HD 13611, BD+

80^{°} 670

, HR 5692, and HD 202109, respectively. Our results suggest that these five Ba stars have a prominent s-process signature, which indicates that their heavy elements mainly come from their former AGB companions (now WDs) by mass transfer, while the r-process contribution can naturally be explained by the evolution of the Milky Way. The s-process contribution of BD+

80^{°} 670

is

51.4 \pm 31.4 %

, which is the lowest among our seven sample stars. Considering its lower values of both [Ba/Nd] and [Ba/Eu], we suspect that BD+

68^{°} 1027

is likely to be a r-rich Ba star and has similar origins to the CEMP-r/s stars. HD 218356 has an unreasonable s-process contribution over

100 %

. Combining its stellar atmospheric parameters and the evolutionary stage, we speculate that HD 218356 is a more evolved extrinsic Ba star, and its massive companion should have the largest s-process efficiency in our samples. Full article

(This article belongs to the Section Solar and Stellar Physics)

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13 pages, 311 KiB

Open AccessArticle

Ricci Soliton and Certain Related Metrics on a Three-Dimensional Trans-Sasakian Manifold

by Zhizhi Chen, Yanlin Li, Sumanjit Sarkar, Santu Dey and Arindam Bhattacharyya

Universe 2022, 8(11), 595; https://doi.org/10.3390/universe8110595 - 11 Nov 2022

Cited by 8 | Viewed by 1570

Abstract

In this article, a Ricci soliton and *-conformal Ricci soliton are examined in the framework of trans-Sasakian three-manifold. In the beginning of the paper, it is shown that a three-dimensional trans-Sasakian manifold of type

(α, β)

admits a Ricci soliton [...] Read more.

In this article, a Ricci soliton and *-conformal Ricci soliton are examined in the framework of trans-Sasakian three-manifold. In the beginning of the paper, it is shown that a three-dimensional trans-Sasakian manifold of type

(α, β)

admits a Ricci soliton where the covariant derivative of potential vector field V in the direction of unit vector field

ξ

is orthogonal to

ξ

. It is also demonstrated that if the structure functions meet

α^{2} = β^{2}

, then the covariant derivative of V in the direction of

ξ

is a constant multiple of

ξ

. Furthermore, the nature of scalar curvature is evolved when the manifold of type

(α, β)

satisfies *-conformal Ricci soliton, provided

α \neq 0

. Finally, an example is presented to verify the findings. Full article

(This article belongs to the Special Issue Research on Optical Soliton Perturbation)

28 pages, 848 KiB

Open AccessArticle

The Primordial Particle Accelerator of the Cosmos

by Asher Yahalom

Universe 2022, 8(11), 594; https://doi.org/10.3390/universe8110594 - 11 Nov 2022

Cited by 3 | Viewed by 1732

Abstract

In a previous paper we have shown that superluminal particles are allowed by the general relativistic theory of gravity provided that the metric is locally Euclidean. Here we calculate the probability density function of a canonical ensemble of superluminal particles as function of [...] Read more.

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

(This article belongs to the Section Cosmology)

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14 pages, 1334 KiB

Open AccessArticle

A Correction Algorithm of the Sampling Effect and Its Application in High-Precision Astrometry

by Yunqi Sun and Jianfeng Zhou

Universe 2022, 8(11), 593; https://doi.org/10.3390/universe8110593 - 11 Nov 2022

Viewed by 1262

Abstract

The sampling effect of the imaging acquisition device is an integration of the input signal within the pixel, resulting in an additional error in the pixel value. Additionally, a sampler with asymmetric intra-pixel quantum efficiency leads to position errors in high-precision astrometry. This [...] Read more.

The sampling effect of the imaging acquisition device is an integration of the input signal within the pixel, resulting in an additional error in the pixel value. Additionally, a sampler with asymmetric intra-pixel quantum efficiency leads to position errors in high-precision astrometry. This paper proposes a model for the integral sampling process. An algorithm that solves the sampling effect, as well as the position error with high accuracy, is also provided. This algorithm provides an accuracy increase of

10^{6}

for Gaussian images with a uniform integral sampler. The accuracy limit of the Gaussian image comes from the truncation error. Also, this algorithm provides about 4 times accuracy improvement by eliminating the systematic error caused by the integral sampler with asymmetric intra-pixel quantum efficiency. Full article

(This article belongs to the Section Space Science)

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19 pages, 650 KiB

Open AccessArticle

Construction of Exact Solutions for Gilson–Pickering Model Using Two Different Approaches

by Hamood Ur Rehman, Aziz Ullah Awan, ElSayed M. Tag-ElDin, Uzma Bashir and Seham Ayesh Allahyani

Universe 2022, 8(11), 592; https://doi.org/10.3390/universe8110592 - 8 Nov 2022

Cited by 11 | Viewed by 1721

Abstract

In this paper, the extended simple equation method (ESEM) and the generalized Riccati equation mapping (GREM) method are applied to the nonlinear third-order Gilson–Pickering (GP) model to obtain a variety of new exact wave solutions. With the suitable selection of parameters involved in [...] Read more.

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

(This article belongs to the Special Issue Research on Optical Soliton Perturbation)

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16 pages, 4234 KiB

Open AccessArticle

Modeling of the Wind/Disk Outflow from Be Stars II: Formation of the Keplerian Disk

by Sergey Bogovalov and Maxim Petrov

Universe 2022, 8(11), 591; https://doi.org/10.3390/universe8110591 - 7 Nov 2022

Viewed by 1476

Abstract

Computer modeling of the outflow from Be stars is performed. In our approach, processes of turbulence excitation and turbulent viscosity are added to the conventional model of the radiation driven winds. The objective of our study is to reproduce from the first principles [...] Read more.

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

(This article belongs to the Section Solar and Stellar Physics)

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19 pages, 1168 KiB

Open AccessArticle

Strangeness Production from Proton–Proton Collisions at Different Energies by Using Monte Carlo Simulation

by Ahmed Hussein, M. A. Mahmoud, Ayman A. Aly, M. N. El-Hammamy and Yasser Mohammed

Universe 2022, 8(11), 590; https://doi.org/10.3390/universe8110590 - 7 Nov 2022

Cited by 1 | Viewed by 1567

Abstract

Nuclear matter, at sufficiently energy density and high temperature, undergoes a transition to a state of strongly interacting QCD matter in which quarks and gluons are not confined known as the Quark–Gluon Plasma (QGP). QGP is usually produced in high-energy collisions of heavy [...] Read more.

Nuclear matter, at sufficiently energy density and high temperature, undergoes a transition to a state of strongly interacting QCD matter in which quarks and gluons are not confined known as the Quark–Gluon Plasma (QGP). QGP is usually produced in high-energy collisions of heavy nuclei in the laboratory, where an enhancement of strange hadrons’ production is observed. Many of the effects which are typical of heavy ion phenomenology have been observed in high-multiplicity proton–proton (pp) collisions. The enhancement of strange particles’ production in pp collisions was reported at

\sqrt{s} = 7

TeV and

\sqrt{s} = 13

TeV in 2017 and 2020, respectively, and it was found that the integrated yields of strange particles, relative to pions, increase notably with the charged-particle multiplicity of events. Here, we report the multiplicity dependence of strange particles at

| y | < 0.5

in pp collisions at

\sqrt{s}

= 7 TeV, 13 TeV, 20 TeV, and 27 TeV from a Monte Carlo simulation using PYTHIA8, EPOS-LHC, and Herwig7. Full article

(This article belongs to the Special Issue Advance in Quark-Gluon-Plasma (QGP) Physics)

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17 pages, 2944 KiB

Open AccessArticle

Astroparticle Constraints from the Cosmic Star Formation Rate Density at High Redshift: Current Status and Forecasts for JWST

by Giovanni Gandolfi, Andrea Lapi, Tommaso Ronconi and Luigi Danese

Universe 2022, 8(11), 589; https://doi.org/10.3390/universe8110589 - 7 Nov 2022

Cited by 8 | Viewed by 1800

Abstract

We exploit the recent determination of the cosmic star formation rate (SFR) density at high redshifts

z ≳ 4

to derive astroparticle constraints on three common dark matter (DM) scenarios alternative to standard cold dark matter (CDM): warm dark matter (WDM), fuzzy dark [...] Read more.

We exploit the recent determination of the cosmic star formation rate (SFR) density at high redshifts

z ≳ 4

to derive astroparticle constraints on three common dark matter (DM) scenarios alternative to standard cold dark matter (CDM): warm dark matter (WDM), fuzzy dark matter (

ψ

DM) and self-interacting dark matter (SIDM). Our analysis relies on the ultraviolet (UV) luminosity functions measured from blank field surveys by the Hubble Space Telescope out to

z ≲ 10

and down to UV magnitudes

M_{UV} ≲ - 17

. We extrapolate these to fainter yet unexplored magnitude ranges and perform abundance matching with the halo mass functions in a given DM scenario, thus, obtaining a redshift-dependent relationship between the UV magnitude and the halo mass. We then computed the cosmic SFR density by integrating the extrapolated UV luminosity functions down to a faint magnitude limit

M_{UV}^{\lim}

, which is determined via the above abundance matching relationship by two free parameters: the minimum threshold halo mass

M_{H}^{GF}

for galaxy formation, and the astroparticle quantity X characterizing each DM scenario (namely, particle mass for WDM and

ψ

DM, and kinetic temperature at decoupling

T_{X}

for SIDM). We perform Bayesian inference on such parameters using a Monte Carlo Markov Chain (MCMC) technique by comparing the cosmic SFR density from our approach to the current observational estimates at

z ≳ 4

, constraining the WDM particle mass to

m_{X} \approx 1 . 2_{- 0.4 (- 0.5)}^{+ 0.3 (11.3)}

keV, the

ψ

DM particle mass to

m_{X} \approx 3 . 7_{- 0.4 (- 0.5)}^{+ 1.8 (+ 12.9 . 3)} \times 10^{- 22}

eV, and the SIDM temperature to

T_{X} \approx 0 . 21_{- 0.06 (- 0.07)}^{+ 0.04 (+ 1.8)}

keV at

68 %

(

95 %

) confidence level. Finally, we forecast how such constraints will be strengthened by upcoming refined estimates of the cosmic SFR density if the early data on the UV luminosity function at

z ≳ 10

from the James Webb Space Telescope (JWST) will be confirmed down to ultra-faint magnitudes. Full article

(This article belongs to the Section Cosmology)

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19 pages, 775 KiB

Open AccessArticle

Afterglow Light Curves from Off-Axis GRB Jets in Stratified Circumburst Medium

by Xiao-Hong Zhao and Kang-Fa Cheng

Universe 2022, 8(11), 588; https://doi.org/10.3390/universe8110588 - 7 Nov 2022

Cited by 1 | Viewed by 1599

Abstract

We study the gamma-ray burst (GRB) afterglow light curves produced by an off-axis jet in a stratified circumburst medium and summarize the temporal indices of the coasting phase, the deceleration phase, the Newtonian phase, and the deep Newtonian phase for various viewing angles [...] Read more.

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

(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)

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222 pages, 2537 KiB

Open AccessEditor’s ChoiceArticle

A New Sample of Gamma-Ray Emitting Jetted Active Galactic Nuclei

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

Universe 2022, 8(11), 587; https://doi.org/10.3390/universe8110587 - 4 Nov 2022

Cited by 22 | Viewed by 3807

Abstract

We considered the fourth catalog of gamma-ray point sources produced by the Fermi Large Area Telescope (LAT) and selected only jetted active galactic nuclei (AGN) or sources with no specific classification, but with a low-frequency counterpart. Our final list is composed of 2980 [...] Read more.

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

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

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14 pages, 304 KiB

Open AccessReview

Covariant Derivative of Fermions and All That

by Ilya L. Shapiro

Universe 2022, 8(11), 586; https://doi.org/10.3390/universe8110586 - 4 Nov 2022

Cited by 26 | Viewed by 1463

Abstract

We present detailed pedagogical derivation of covariant derivative of fermions and some related expressions, including commutator of covariant derivatives and energy-momentum tensor of a free Dirac field. On top of that, local conformal transformations for a Dirac fermion in curved spacetime are considered [...] Read more.

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

(This article belongs to the Section High Energy Nuclear and Particle Physics)

17 pages, 1454 KiB

Open AccessArticle

Explaining the Multiwavelength Emission of γ-ray Bright Flat-Spectrum Radio Quasar 3C 454.3 in Different Activity States

by Yaru Feng, Shaoming Hu, Ruixin Zhou and Songbo Gao

Universe 2022, 8(11), 585; https://doi.org/10.3390/universe8110585 - 4 Nov 2022

Cited by 1 | Viewed by 1665

Abstract

The origin of gamma-ray flares of blazars is still an open issue in jet physics. In this work, we reproduce the multiwavelength spectral energy distribution (SED) of flat-spectrum radio quasars 3C 454.3 under a one-zone leptonic scenario, investigate the variation of the physical [...] Read more.

The origin of gamma-ray flares of blazars is still an open issue in jet physics. In this work, we reproduce the multiwavelength spectral energy distribution (SED) of flat-spectrum radio quasars 3C 454.3 under a one-zone leptonic scenario, investigate the variation of the physical parameters in different activity states, and analyze the possible origin of its

γ

-ray outburst. Based on the analysis of multiwavelength quasi-simultaneous observations of 3C 454.3 during MJD 55,400–56,000, we consider that the radiation includes synchrotron (Syn), synchrotron self-Compton (SSC), and external Compton (EC) radiations by the simulation, and the seed photons of the external Compton component mainly comes from the broad-line region and dusty molecular torus. The model results show that: (1) We can well reproduce the multiwavelength quasi-simultaneity SED of 3C 454.3 in various activity states by using a one-zone Syn+SSC+EC model. (2) By comparing the physical model parameters of the bright and the quiescent states, we suggest that this

γ

-ray flaring activity is more likely to be caused by the increase in the doppler factor. Full article

(This article belongs to the Special Issue Multi-Messengers of Black Hole Accretion and Emission)

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12 pages, 2299 KiB

Open AccessArticle

Two Analytical Schemes for the Optical Soliton Solution of the (2 + 1) Hirota–Maccari System Observed in Single-Mode Fibers

by Neslihan Ozdemir, Aydin Secer, Muslum Ozisik and Mustafa Bayram

Universe 2022, 8(11), 584; https://doi.org/10.3390/universe8110584 - 4 Nov 2022

Cited by 6 | Viewed by 1645

Abstract

In this scientific research article, the new Kudryashov method and the tanh-coth method, which have not been applied before, are employed to construct analytical and soliton solutions of the

(2 + 1)

-dimensional Hirota–Maccari system. The

(2 + 1)

[...] Read more.

In this scientific research article, the new Kudryashov method and the tanh-coth method, which have not been applied before, are employed to construct analytical and soliton solutions of the

(2 + 1)

-dimensional Hirota–Maccari system. The

(2 + 1)

-dimensional Hirota–Maccari system is a special kind of nonlinear Schrödinger equation (NLSEs) that models the motion of isolated waves localized in a small part of space, and is used in such various fields as fiber optics telecommunication systems, nonlinear optics, plasma physics, and hydrodynamics. In addition, the Hirota–Maccari system defines the dynamical characters of femtosecond soliton pulse propagation in single-mode fibers. Analytical solutions of the model are successfully acquired with the assistance of symbolic computation utilizing these methods. Finally, 3D, 2D, and contour graphs of solutions are depicted at specific values of parameters. It is shown that the new Kudryashov method and the tanh-coth method are uncomplicated, very effective, easily applicable, reliable, and indeed vital mathematical tools in solving nonlinear models. Full article

(This article belongs to the Special Issue Research on Optical Soliton Perturbation)

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24 pages, 2264 KiB

Open AccessReview

On General-Relativistic Lagrangian Perturbation Theory and Its Non-Perturbative Generalization

by Thomas Buchert, Ismael Delgado Gaspar and Jan Jakub Ostrowski

Universe 2022, 8(11), 583; https://doi.org/10.3390/universe8110583 - 4 Nov 2022

Cited by 5 | Viewed by 1972

Abstract

The Newtonian Lagrangian perturbation theory is a widely used framework to study structure formation in cosmology in the nonlinear regime. We review a general-relativistic formulation of such a perturbation approach, emphasizing results on an already developed extensive formalism including among other aspects: the [...] Read more.

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

(This article belongs to the Special Issue Cosmological Perturbations in Early and Late Cosmology-in Honor of Professor Maurizio Gasperini on the Occasion of His 70th Birthday)

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12 pages, 471 KiB

Open AccessArticle

Pasta Phases in Neutron Star Mantle: Extended Thomas–Fermi vs. Compressible Liquid Drop Approaches

by Nikolai N. Shchechilin, Nikita A. Zemlyakov, Andrey I. Chugunov and Mikhail E. Gusakov

Universe 2022, 8(11), 582; https://doi.org/10.3390/universe8110582 - 4 Nov 2022

Cited by 5 | Viewed by 1459

Abstract

Nuclear pasta phases in the neutron stars mantle can affect the mechanical and transport properties of superdense matter, thus playing an important role in the dynamics and evolution of neutron stars. In this paper, we compare results obtained by the Extended Thomas–Fermi (ETF) [...] Read more.

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

(This article belongs to the Section Compact Objects)

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16 pages, 591 KiB

Open AccessArticle

Galactic Wormhole under Lovelock Gravity

by Koushik Chakraborty, Farook Rahaman, Saibal Ray, Banashree Sen and Debabrata Deb

Universe 2022, 8(11), 581; https://doi.org/10.3390/universe8110581 - 3 Nov 2022

Cited by 9 | Viewed by 1786

Abstract

We explore wormhole geometry in spiral galaxies under the third order Lovelock gravity. Using the cubic spline interpolation technique, we find the rotational velocity of test particles in the halo region of our spiral galaxy from observed values of radial distances and rotational [...] Read more.

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

(This article belongs to the Collection Modified Theories of Gravity and Cosmological Applications)

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9 pages, 354 KiB

Open AccessCommunication

A Wheeler–DeWitt Equation with Time

by Marcello Rotondo

Universe 2022, 8(11), 580; https://doi.org/10.3390/universe8110580 - 3 Nov 2022

Cited by 2 | Viewed by 1682

Abstract

The equation for canonical gravity produced by Wheeler and DeWitt in the late 1960s still presents difficulties both in terms of its mathematical solution and its physical interpretation. One of these issues is, notoriously, the absence of an explicit time. In this short [...] Read more.

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

(This article belongs to the Section Foundations of Quantum Mechanics and Quantum Gravity)

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