Next Issue
Volume 8, May
Previous Issue
Volume 8, March
 
 

Universe, Volume 8, Issue 4 (April 2022) – 53 articles

Cover Story (view full-size image): Neutrino propagation in curved spacetime backgrounds has always attracted considerable attention, as it can provide a valuable insight into both the particle’s intrinsic features and the underlying gravitational field with which it interacts. By virtue of the above premise, one can study this phenomenon in the presence of a Schwarzschild spacetime with the addition of quantum corrections evaluated in the framework of perturbative quantum gravity at lowest order. The ensuing neutrino oscillations and decoherence mechanism can then be described by relying on the non-covariant Gaussian wave packet description, finding that quantum gravity corrections significantly affect the properties of mixed particles and induce potentially measurable physical effects. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Select all
Export citation of selected articles as:
12 pages, 1307 KiB  
Article
GRB 181110A: Constraining the Jet Structure, Circumburst Medium and the Initial Lorentz Factor
by Song Han, Xinyu Li, Luyao Jiang, Zhiping Jin, Haoning He, Yuanzhu Wang and Daming Wei
Universe 2022, 8(4), 248; https://doi.org/10.3390/universe8040248 - 18 Apr 2022
Cited by 2 | Viewed by 1852
Abstract
The afterglow data of gamma ray bursts (GRBs) can be used to constrain the physical properties of the fireball (e.g., the jet structure and opening angle) and the circumburst medium. With the peak time of the early afterglow light curve being taken as [...] Read more.
The afterglow data of gamma ray bursts (GRBs) can be used to constrain the physical properties of the fireball (e.g., the jet structure and opening angle) and the circumburst medium. With the peak time of the early afterglow light curve being taken as the deceleration time, one can estimate the initial Lorentz factor of the fireball. In this work, we perform a comprehensive analysis on the prompt emission and the afterglow data of GRB 181110A, where a clear peak is detected by Swift UVOT and XRT in optical to X-ray bands. Prompt emission spectral analysis shows that the spectrum of GRB 181110A is soft, and both hard-to-soft and intensity-tracking spectral evolution are found. By fitting the afterglow light curve and building spectral energy distribution, we find that the standard external forward shock model with a constant circumburst medium is favored, and the jet structure of GRB 181110A tends to be uniform rather than structured. With the peak time of early afterglow emission, we estimate the initial fireball Lorentz factor of GRB 181110A to be Γ0=16940+92. We also compare GRB 181110A with other typical long GRBs in a statistical context. Full article
(This article belongs to the Special Issue Advances in Astrophysics and Cosmology – in Memory of Prof. Tan Lu)
Show Figures

Figure 1

27 pages, 397 KiB  
Article
Einstein Field Equation, Recursion Operators, Noether and Master Symmetries in Conformable Poisson Manifolds
by Mahouton Norbert Hounkonnou, Mahougnon Justin Landalidji and Melanija Mitrović
Universe 2022, 8(4), 247; https://doi.org/10.3390/universe8040247 - 17 Apr 2022
Cited by 2 | Viewed by 1726
Abstract
We show that a Minkowski phase space endowed with a bracket relatively to a conformable differential realizes a Poisson algebra, confering a bi-Hamiltonian structure to the resulting manifold. We infer that the related Hamiltonian vector field is an infinitesimal Noether symmetry, and compute [...] Read more.
We show that a Minkowski phase space endowed with a bracket relatively to a conformable differential realizes a Poisson algebra, confering a bi-Hamiltonian structure to the resulting manifold. We infer that the related Hamiltonian vector field is an infinitesimal Noether symmetry, and compute the corresponding deformed recursion operator. Besides, using the Hamiltonian–Jacobi separability, we construct recursion operators for Hamiltonian vector fields in conformable Poisson–Schwarzschild and Friedmann–Lemaître–Robertson–Walker (FLRW) manifolds, and derive the related constants of motion, Christoffel symbols, components of Riemann and Ricci tensors, Ricci constant and components of Einstein tensor. We highlight the existence of a hierarchy of bi-Hamiltonian structures in both the manifolds, and compute a family of recursion operators and master symmetries generating the constants of motion. Full article
(This article belongs to the Special Issue Selected Topics in Gravity, Field Theory and Quantum Mechanics)
Show Figures

Figure 1

25 pages, 2434 KiB  
Article
Multipomeron Model with Collective Effects for High-Energy Hadron Collisions
by Vladimir Kovalenko, Grigorii Feofilov, Andrei Puchkov and Farkhat Valiev
Universe 2022, 8(4), 246; https://doi.org/10.3390/universe8040246 - 16 Apr 2022
Cited by 9 | Viewed by 1987
Abstract
We propose the generalized multipomeron exchange model for multiparticle production in high-energy proton–proton, proton–nucleus and heavy-ion collisions. For all of these systems, we consider collectivity effects based on the quark–gluon string fusion concept, where new types of particle-emitting sources—strings with higher tension—are produced. [...] Read more.
We propose the generalized multipomeron exchange model for multiparticle production in high-energy proton–proton, proton–nucleus and heavy-ion collisions. For all of these systems, we consider collectivity effects based on the quark–gluon string fusion concept, where new types of particle-emitting sources—strings with higher tension—are produced. We obtained the model parameters using the data on the multiplicity dependence of the mean transverse momentum of charged particles in pp and pp¯ collisions over a wide energy range (from ISR to LHC). We calculated the yields of strange, multi-strange and charm particles as a function of multiplicity for pp, p-Pb and Pb-Pb collisions at the LHC energy and compared the results with the experimental data. Full article
(This article belongs to the Special Issue Universe: Feature Papers–High Energy Nuclear and Particle Physics)
Show Figures

Figure 1

15 pages, 274 KiB  
Article
Maxwell’s Equations in Homogeneous Spaces for Admissible Electromagnetic Fields
by Valery V. Obukhov
Universe 2022, 8(4), 245; https://doi.org/10.3390/universe8040245 - 15 Apr 2022
Cited by 13 | Viewed by 1718
Abstract
Maxwell’s vacuum equations are integrated for admissible electromagnetic fields in homogeneous spaces. Admissible electromagnetic fields are those for which the space group generates an algebra of symmetry operators (integrals of motion) that is isomorphic to the algebra of group operators. Two frames associated [...] Read more.
Maxwell’s vacuum equations are integrated for admissible electromagnetic fields in homogeneous spaces. Admissible electromagnetic fields are those for which the space group generates an algebra of symmetry operators (integrals of motion) that is isomorphic to the algebra of group operators. Two frames associated with the group of motions are used to obtain systems of ordinary differential equations to which Maxwell’s equations reduce. The solutions are obtained in quadratures. The potentials of the admissible electromagnetic fields and the metrics of the spaces contained in the obtained solutions depend on six arbitrary time functions, so it is possible to use them to integrate field equations in the theory of gravity. Full article
(This article belongs to the Special Issue Selected Topics in Gravity, Field Theory and Quantum Mechanics)
16 pages, 630 KiB  
Article
Nonsingular Black Holes in 4D Einstein–Gauss–Bonnet Gravity
by Arun Kumar, Dharmanand Baboolal and Sushant G. Ghosh
Universe 2022, 8(4), 244; https://doi.org/10.3390/universe8040244 - 14 Apr 2022
Cited by 10 | Viewed by 1976
Abstract
Recently, several methods have been proposed to regularize a D4 limit of Einstein–Gauss–Bonnet (EGB), leading to nontrivial gravitational dynamics in 4D. We present an exact nonsingular black hole solution in the 4D EGB gravity coupled to non-linear electrodynamics [...] Read more.
Recently, several methods have been proposed to regularize a D4 limit of Einstein–Gauss–Bonnet (EGB), leading to nontrivial gravitational dynamics in 4D. We present an exact nonsingular black hole solution in the 4D EGB gravity coupled to non-linear electrodynamics and analyze their thermodynamic properties to calculate precise expressions for the black hole mass, temperature, and entropy. Because of the magnetic charge, the thermodynamic quantities are corrected, and the Hawking–Page phase transition is achievable with diverges of the heat capacity at a larger critical radius r=r+C in comparison to the 5D counterpart where the temperature is maximum. Thus, we have a black hole with Cauchy and event horizons, and its evaporation leads to a thermodynamically stable extremal black hole remnant with vanishing temperature, and its size is larger than the 5D counterpart. The entropy does not satisfy the usual exact horizon Bekenstein–Hawking area law of general relativity with a logarithmic area correction term. Full article
Show Figures

Figure 1

11 pages, 1560 KiB  
Article
The Initial-Final Mass Relation of White Dwarfs: A Tool to Calibrate the Third Dredge-Up
by Paola Marigo
Universe 2022, 8(4), 243; https://doi.org/10.3390/universe8040243 - 14 Apr 2022
Cited by 7 | Viewed by 1472
Abstract
The initial mass-final mass relationship (IFMR) of white dwarfs (WD) represents a crucial benchmark for stellar evolution models, especially for the efficiency of mixing episodes and mass loss during the asymptotic giant branch (AGB) phase. In this study, we argue that this relation [...] Read more.
The initial mass-final mass relationship (IFMR) of white dwarfs (WD) represents a crucial benchmark for stellar evolution models, especially for the efficiency of mixing episodes and mass loss during the asymptotic giant branch (AGB) phase. In this study, we argue that this relation offers the opportunity to constrain the third dredge-up (3DU), with important consequences for chemical yields. The results are discussed in light of recent studies that have identified a kink in the IFMR for initial masses close to 2M. Adopting a physically-sound approach in which the efficiency λ of the 3DU varies as a function of core and envelope masses, we calibrate λ in solar-metallicity TP-AGB models in order to reproduce the final masses of their WD progeny, over the range of initial masses 0.9Mi/M6. In particular, we find that in low-mass stars with 1.4Mi/M2.0 the efficiency is small, λ0.3, it steeply rises to about λ0.65 in intermediate-mass stars with 2.0Mi/M4.0, and then it drops in massive TP-AGB stars with 4.0Mi/M6.0. Our study also suggests that a second kink may show up in the IFMR at the transition between the most massive carbon stars and those that are dominated by hot-bottom burning. Full article
Show Figures

Figure 1

8 pages, 1202 KiB  
Communication
Analogue Quantum Gravity in Hyperbolic Metamaterials
by Igor I. Smolyaninov and Vera N. Smolyaninova
Universe 2022, 8(4), 242; https://doi.org/10.3390/universe8040242 - 14 Apr 2022
Cited by 3 | Viewed by 1987
Abstract
It is well known that extraordinary photons in hyperbolic metamaterials may be described as living in an effective Minkowski spacetime, which is defined by the peculiar form of the strongly anisotropic dielectric tensor in these metamaterials. Here, we demonstrate that within the scope [...] Read more.
It is well known that extraordinary photons in hyperbolic metamaterials may be described as living in an effective Minkowski spacetime, which is defined by the peculiar form of the strongly anisotropic dielectric tensor in these metamaterials. Here, we demonstrate that within the scope of this approximation, the sound waves in hyperbolic metamaterials look similar to gravitational waves, and therefore the quantized sound waves (phonons) look similar to gravitons. Such an analogue model of quantum gravity looks especially interesting near the phase transitions in hyperbolic metamaterials where it becomes possible to switch quantum gravity effects on and off as a function of metamaterial temperature. We also predict strong enhancement of sonoluminescence in ferrofluid-based hyperbolic metamaterials, which looks analogous to particle creation in strong gravitational fields. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Show Figures

Figure 1

16 pages, 5578 KiB  
Article
Directional-Sensitive X-ray/Gamma-ray Imager on Board the VZLUSAT-2 CubeSat for Wide Field-of-View Observation of GRBs in Low Earth Orbit
by Carlos Granja, Rene Hudec, Veronika Maršíková, Adolf Inneman, Ladislav Pína, Daniela Doubravova, Zdenek Matej, Vladimir Daniel and Peter Oberta
Universe 2022, 8(4), 241; https://doi.org/10.3390/universe8040241 - 13 Apr 2022
Cited by 4 | Viewed by 2107
Abstract
We present a miniaturized and wide field-of-view X-ray and Gamma-ray imager consisting of a segmented 2D optics-collimator coupled to the high-sensitivity semiconductor pixel detector Timepix equipped with a high-Z sensor (CdTe 2000 μm thick). The compact payload has been deployed in low-Earth [...] Read more.
We present a miniaturized and wide field-of-view X-ray and Gamma-ray imager consisting of a segmented 2D optics-collimator coupled to the high-sensitivity semiconductor pixel detector Timepix equipped with a high-Z sensor (CdTe 2000 μm thick). The compact payload has been deployed in low-Earth orbit (LEO) onboard the 3U Cubesat VZLUSAT-2 which was launched on 13 January 2022. The instrument is designed to verify small spacecraft borne observation in open space of hard X-ray and Gamma-ray sources both of celestial and atmospheric origin. High-resolution spectral-sensitive X-ray and Gamma-ray images are provided with enhanced event discrimination and wide field-of-view up to 60°. Description of the instrument together with response evaluation and tests in ground with well-defined sources are presented. The intended observational plan for in-orbit measurements is outlined along with astrophysical goals and issues. Full article
Show Figures

Figure 1

14 pages, 2041 KiB  
Article
Observational Constraints and Some Toy Models in f(Q) Gravity with Bulk Viscous Fluid
by Sanjay Mandal, Abhishek Parida and Pradyumn Kumar Sahoo
Universe 2022, 8(4), 240; https://doi.org/10.3390/universe8040240 - 13 Apr 2022
Cited by 21 | Viewed by 2090
Abstract
The standard formulation of general relativity fails to describe some recent interests in the universe. It impels us to go beyond the standard formulation of gravity. The f(Q) gravity theory is an interesting modified theory of gravity, where the gravitational [...] Read more.
The standard formulation of general relativity fails to describe some recent interests in the universe. It impels us to go beyond the standard formulation of gravity. The f(Q) gravity theory is an interesting modified theory of gravity, where the gravitational interaction is driven by the nonmetricity Q. This study aims to examine the cosmological models with the presence of bulk viscosity effect in the cosmological fluid within the framework of f(Q) gravity. We construct three bulk viscous fluid models, i.e., (i) for the first model, we assuming the Lagrangian f(Q) as linear dependence on Q, (ii) for the second model the Lagrangian f(Q) as a polynomial functional form, and (iii) the Lagrangian f(Q) as a logarithmic dependence on Q. Furthermore, we use 57 points of Hubble data and 1048 Pantheon dataset to constrain the model parameters. Then, we discuss all the energy conditions for each model, which helps us to test the self-consistency of our models. Finally, we present the profiles of the equation of state parameters to test the models’ present status. Full article
Show Figures

Figure 1

5 pages, 697 KiB  
Editorial
Editorial to the Special Issue “Advances in the Physics of Stars—In Memory of Prof. Yuri N. Gnedin”
by Nazar R. Ikhsanov, Galina L. Klimchitskaya and Vladimir M. Mostepanenko
Universe 2022, 8(4), 239; https://doi.org/10.3390/universe8040239 - 13 Apr 2022
Viewed by 1740
Abstract
This Special Issue collects articles devoted to various aspects of astrophysics which can be understood as a science investigating stars, galaxies, their types and properties, stages of their evolution, distribution in the Universe and the interstellar and intergalactic media [...] Full article
(This article belongs to the Special Issue Advances in the Physics of Stars - in Memory of Prof. Yuri N. Gnedin)
Show Figures

Figure 1

9 pages, 587 KiB  
Article
Non-Unitary Neutrino Mixing in the NOνA Near Detector Data
by Ushak Rahaman and Soebur Razzaque
Universe 2022, 8(4), 238; https://doi.org/10.3390/universe8040238 - 13 Apr 2022
Cited by 3 | Viewed by 1615
Abstract
The νμνe oscillation probability over a short baseline (≲1 km) would be negligible for the case when the mixing matrix for three active neutrinos is unitary. However, in the case of a non-unitary mixing of three neutrinos, this probability [...] Read more.
The νμνe oscillation probability over a short baseline (≲1 km) would be negligible for the case when the mixing matrix for three active neutrinos is unitary. However, in the case of a non-unitary mixing of three neutrinos, this probability would be non-negligible due to the so-called “zero distance” effect. Hence, the near detector of accelerator experiments such as NOνA can provide strong constraints on the parameters of the non-unitary mixing with very large statistics. By analyzing the NOνA near-detector data, we find that the non-unitary mixing does not improve fits to the νe or νμ events over the standard unitary mixing. This leads to constraints on the non-unitary parameters: α00>0.911, |α10|<0.020, and α11>0.952 at 90% C.L. A combined analysis with the near- and far-detector data does not change these constraints significantly. Full article
(This article belongs to the Special Issue Recent Advances in Neutrino Physics: From Theory to Experiments)
Show Figures

Figure 1

19 pages, 454 KiB  
Article
Lorentzian Vacuum Transitions in Hořava–Lifshitz Gravity
by Hugo García-Compeán and Daniel Mata-Pacheco
Universe 2022, 8(4), 237; https://doi.org/10.3390/universe8040237 - 12 Apr 2022
Cited by 10 | Viewed by 1446
Abstract
The vacuum transition probabilities for a Friedmann–Lemaître–Robertson–Walker universe with positive curvature in Hořava–Lifshitz gravity in the presence of a scalar field potential in the Wentzel–Kramers–Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to [...] Read more.
The vacuum transition probabilities for a Friedmann–Lemaître–Robertson–Walker universe with positive curvature in Hořava–Lifshitz gravity in the presence of a scalar field potential in the Wentzel–Kramers–Brillouin approximation are studied. We use a general procedure to compute such transition probabilities using a Hamiltonian approach to the Wheeler–DeWitt equation presented in a previous work. We consider two situations of scalar fields, one in which the scalar field depends on all the spacetime variables and another in which the scalar field depends only on the time variable. In both cases, analytic expressions for the vacuum transition probabilities are obtained, and the infrared and ultraviolet limits are discussed for comparison with the result obtained by using general relativity. For the case in which the scalar field depends on all spacetime variables, we observe that in the infrared limit it is possible to obtain a similar behavior as in general relativity, however, in the ultraviolet limit the behavior found is completely opposite. Some few comments about possible phenomenological implications of our results are given. One of them is a plausible resolution of the initial singularity. On the other hand, for the case in which the scalar field depends only on the time variable, the behavior coincides with that of general relativity in both limits, although in the intermediate region the probability is slightly altered. Full article
(This article belongs to the Special Issue Quantum Gravity Phenomenology)
Show Figures

Figure 1

12 pages, 3816 KiB  
Article
Significant Variations of Thermospheric Nitric Oxide Cooling during the Minor Geomagnetic Storm on 6 May 2015
by Zheng Li, Meng Sun, Jingyuan Li, Kedeng Zhang, Hua Zhang, Xiaojun Xu and Xinhua Zhao
Universe 2022, 8(4), 236; https://doi.org/10.3390/universe8040236 - 12 Apr 2022
Cited by 7 | Viewed by 2028
Abstract
Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling [...] Read more.
Using observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics) satellite and simulations by the TIEGCM (Thermosphere-Ionosphere-Electrodynamics General Circulation Model), we investigate the daytime variations of thermospheric nitric oxide (NO) cooling during the geomagnetic storm on 6 May 2015. The geomagnetic storm was minor, as the minimum Dst was −28 nT, the maximum Kp was 5+ and the maximum AE was 1259 nT. However, significant enhancements of peak NO cooling rate and prominent decreases in the peak NO cooling altitude were observed from high latitudes to low latitudes in both hemispheres on the dayside by the SABER instrument. The model simulations underestimate the response of peak NO cooling and have no significant variation of the altitude of peak NO cooling rate on the dayside during this minor geomagnetic storm. By investigating the temporal and latitudinal variations of vertical NO cooling profiles inferred from SABER data, we suggest that the horizontal equatorward winds caused by the minor geomagnetic storm were unexpectedly strong and thus play an important role in inducing these significant daytime NO cooling variations. Full article
(This article belongs to the Special Issue Space Weather in the Sun–Earth System)
Show Figures

Figure 1

18 pages, 644 KiB  
Article
Search for Dark Higgs Inflation with Curvature Corrections at LHC Experiments
by Lucia Aurelia Popa
Universe 2022, 8(4), 235; https://doi.org/10.3390/universe8040235 - 12 Apr 2022
Cited by 2 | Viewed by 1855
Abstract
We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological [...] Read more.
We analyse the dark Higgs inflation model with curvature corrections and explore the possibility to test its predictions by the particle physics experiments at LHC. We show that the dark Higgs inflation model with curvature corrections is strongly favoured by the present cosmological observation. The cosmological predictions of this model, including the quantum corrections of dark Higgs coupling constants and the uncertainty in estimation of the reheating temperature, lead to the dark Higgs mass mφ=0.919± 0.211 GeV and the mixing angle (at 68% CL). We evaluate the FASER and MAPP-1 experiments reach for dark Higgs inflation mass and mixing angle in the 95% CL cosmological confidence region for an integrated luminosity of 3ab1 at 13 TeV LHC, assuming 100% detection efficiency. We conclude that the dark Higgs inflation model with curvature corrections is a compelling inflation scenario based on particle physics theory favoured by the present cosmological measurements that can leave imprints in the dark Higgs boson searchers at LHC. Full article
(This article belongs to the Collection Women Physicists in Astrophysics, Cosmology and Particle Physics)
Show Figures

Figure 1

22 pages, 1035 KiB  
Article
CP Violation for the Heavens and the Earth
by George Wei-Shu Hou
Universe 2022, 8(4), 234; https://doi.org/10.3390/universe8040234 - 11 Apr 2022
Viewed by 1563
Abstract
Electroweak baryogenesis can be driven by the top quark in a general two Higgs doublet model with extra Yukawa couplings. Higgs quartics provide the first order phase transition, while extra top Yukawa coupling ρtt can fuel the cosmic baryon asymmetry through [...] Read more.
Electroweak baryogenesis can be driven by the top quark in a general two Higgs doublet model with extra Yukawa couplings. Higgs quartics provide the first order phase transition, while extra top Yukawa coupling ρtt can fuel the cosmic baryon asymmetry through the λtImρtt product, with flavor-changing ρtc coupling as backup. The impressive ACME 2018 bound on the electron electric dipole moment calls for an extra electron coupling ρee for exquisite cancellation among dangerous diagrams, broadening the baryogenesis solution space. The mechanism suggests that extra Yukawa couplings echo the hierarchical structure of standard Yukawa couplings. Phenomenological consequences in the Higgs search and flavor physics are discussed, with μ and τ EDM touched upon. Full article
(This article belongs to the Special Issue Universe: Feature Papers–High Energy Nuclear and Particle Physics)
Show Figures

Figure 1

12 pages, 841 KiB  
Review
Post-AGB Stars as Tracers of AGB Nucleosynthesis: An Update
by Devika Kamath and Hans Van Winckel
Universe 2022, 8(4), 233; https://doi.org/10.3390/universe8040233 - 11 Apr 2022
Cited by 6 | Viewed by 2259
Abstract
The chemical evolution of galaxies is governed by the chemical yields from stars, and here we focus on the important contributions from asymptotic giant branch (AGB) stars. AGB nucleosynthesis is, however, still riddled with complexities. Observations from post-asymptotic giant branch (post-AGB) stars serve [...] Read more.
The chemical evolution of galaxies is governed by the chemical yields from stars, and here we focus on the important contributions from asymptotic giant branch (AGB) stars. AGB nucleosynthesis is, however, still riddled with complexities. Observations from post-asymptotic giant branch (post-AGB) stars serve as exquisite tools to quantify and understand AGB nucleosynthesis. In this contribution, we review the invaluable constraints provided by post-AGB stars with which to study AGB nucleosynthesis, especially the slow neutron capture nucleosynthesis (i.e., the s-process). Full article
Show Figures

Figure 1

14 pages, 539 KiB  
Article
Bardeen Black Holes in the Regularized 4D Einstein–Gauss–Bonnet Gravity
by Arun Kumar, Rahul Kumar Walia and Sushant G. Ghosh
Universe 2022, 8(4), 232; https://doi.org/10.3390/universe8040232 - 10 Apr 2022
Cited by 18 | Viewed by 1860
Abstract
We obtain exact Bardeen black holes to the regularized 4D Einstein–Gauss–Bonnet (EGB) gravity minimally coupled with the nonlinear electrodynamics (NED). In turn, we analyze the horizon structure to determine the effect of GB parameter α on the minimum cutoff values of mass, [...] Read more.
We obtain exact Bardeen black holes to the regularized 4D Einstein–Gauss–Bonnet (EGB) gravity minimally coupled with the nonlinear electrodynamics (NED). In turn, we analyze the horizon structure to determine the effect of GB parameter α on the minimum cutoff values of mass, M0, and magnetic monopole charge, g0, for the existence of a black hole horizon. We obtain an exact expression for thermodynamic quantities, namely, Hawking temperature T+, entropy S+, Helmholtz free energy F+, and specific heat C+ associated with the black hole horizon, and they show significant deviations from the 4D EGB case owing to NED. Interestingly, there exists a critical value of horizon radius, r+c, corresponding to the local maximum of Hawking temperature, at which heat capacity diverges, confirming the second-order phase transition. A discussion on the black holes of alternate regularized 4D EGB gravity belonging to the scalar-tensor theory is appended. Full article
Show Figures

Figure 1

8 pages, 629 KiB  
Communication
Modeling of Magnetospheres of Terrestrial Exoplanets in the Habitable Zone around G-Type Stars
by Elena S. Belenkaya, Igor I. Alexeev and Marina S. Blokhina
Universe 2022, 8(4), 231; https://doi.org/10.3390/universe8040231 - 8 Apr 2022
Cited by 3 | Viewed by 1661
Abstract
Using a paraboloid model of an Earth-like exoplanetary magnetospheric magnetic field, developed from a model of the Earth, we investigate the magnetospheric structure of planets located in the habitable zone around G-type stars. Different directions of the stellar wind magnetic field are considered [...] Read more.
Using a paraboloid model of an Earth-like exoplanetary magnetospheric magnetic field, developed from a model of the Earth, we investigate the magnetospheric structure of planets located in the habitable zone around G-type stars. Different directions of the stellar wind magnetic field are considered and the corresponding variations in the magnetospheric structure are obtained. It is shown that the exoplanetary environment significantly depends on stellar wind magnetic field orientation and that the parameters of magnetospheric current systems depend on the distance to the stand-off magnetopause point. Full article
(This article belongs to the Special Issue Planetary Plasma Environment)
Show Figures

Figure 1

21 pages, 432 KiB  
Article
Polyadic Analogs of Direct Product
by Steven Duplij
Universe 2022, 8(4), 230; https://doi.org/10.3390/universe8040230 - 8 Apr 2022
Cited by 3 | Viewed by 1458
Abstract
We propose a generalization of the external direct product concept to polyadic algebraic structures which introduces novel properties in two ways: the arity of the product can differ from that of the constituents, and the elements from different multipliers can be “entangled” such [...] Read more.
We propose a generalization of the external direct product concept to polyadic algebraic structures which introduces novel properties in two ways: the arity of the product can differ from that of the constituents, and the elements from different multipliers can be “entangled” such that the product is no longer componentwise. The main property which we want to preserve is associativity, which is gained by using the associativity quiver technique, which was provided previously. For polyadic semigroups and groups we introduce two external products: (1) the iterated direct product, which is componentwise but can have an arity that is different from the multipliers and (2) the hetero product (power), which is noncomponentwise and constructed by analogy with the heteromorphism concept introduced earlier. We show in which cases the product of polyadic groups can itself be a polyadic group. In the same way, the external product of polyadic rings and fields is generalized. The most exotic case is the external product of polyadic fields, which can be a polyadic field (as opposed to the binary fields), in which all multipliers are zeroless fields. Many illustrative concrete examples are presented. Full article
(This article belongs to the Special Issue Selected Topics in Gravity, Field Theory and Quantum Mechanics)
30 pages, 405 KiB  
Article
Ultraviolet Finiteness or Asymptotic Safety in Higher Derivative Gravitational Theories
by Lesław Rachwał
Universe 2022, 8(4), 229; https://doi.org/10.3390/universe8040229 - 8 Apr 2022
Viewed by 1470
Abstract
We present and discuss well known conditions for ultraviolet finiteness and asymptotic safety. The requirements for complete absence of ultraviolet divergences in quantum field theories and existence of a non-trivial fixed point for renormalization group flow in the ultraviolet regime are compared based [...] Read more.
We present and discuss well known conditions for ultraviolet finiteness and asymptotic safety. The requirements for complete absence of ultraviolet divergences in quantum field theories and existence of a non-trivial fixed point for renormalization group flow in the ultraviolet regime are compared based on the example of a six-derivative quantum gravitational theory in d=4 spacetime dimensions. In this model, it is possible for the first time to have fully UV-finite quantum theory without adding matter or special symmetry, but by inclusion of additional terms cubic in curvatures. We comment on similarities and some apparent differences between the two approaches, but we show that they are both compatible to each other. Finally, we motivate the claim that actually asymptotic safety needs UV-finite models for providing explicit form of the ultraviolet limit of Wilsonian effective actions describing special situations at fixed points. Full article
(This article belongs to the Special Issue Alternative Gravities and Fundamental Cosmology)
32 pages, 4087 KiB  
Article
Superconducting Phases in Neutron Star Cores
by Toby S. Wood and Vanessa Graber
Universe 2022, 8(4), 228; https://doi.org/10.3390/universe8040228 - 8 Apr 2022
Cited by 12 | Viewed by 1933
Abstract
Using a phenomenological Ginzburg–Landau model that includes entrainment, we identify the possible ground states for the neutron and proton condensates in the core of a neutron star, as a function of magnetic field strength. Combining analytical and numerical techniques, we find that much [...] Read more.
Using a phenomenological Ginzburg–Landau model that includes entrainment, we identify the possible ground states for the neutron and proton condensates in the core of a neutron star, as a function of magnetic field strength. Combining analytical and numerical techniques, we find that much of the outer core is likely to be a “type-1.5” superconductor (instead of a type-II superconductor as often assumed), in which magnetic flux is distributed inhomogeneously, with bundles of magnetic fluxtubes separated by flux-free Meissner regions. We provide an approximate criterion to determine the transition between this type-1.5 phase and the type-I region in the inner core. We also show that bundles of fluxtubes can coexist with non-superconducting regions, but only in a small part of the parameter space. Full article
(This article belongs to the Special Issue Superfluidity and Superconductivity in Neutron Stars)
Show Figures

Figure 1

16 pages, 964 KiB  
Review
Muon to Positron Conversion
by MyeongJae Lee and Michael MacKenzie
Universe 2022, 8(4), 227; https://doi.org/10.3390/universe8040227 - 7 Apr 2022
Cited by 5 | Viewed by 2032
Abstract
Lepton-flavor violation (LFV) has been discovered in the neutrino sector by neutrino oscillation experiments. The minimal extension of the Standard Model (SM) to include neutrino masses allows LFV in the charged sector (CLFV) at the loop level, but at rates that are too [...] Read more.
Lepton-flavor violation (LFV) has been discovered in the neutrino sector by neutrino oscillation experiments. The minimal extension of the Standard Model (SM) to include neutrino masses allows LFV in the charged sector (CLFV) at the loop level, but at rates that are too small to be experimentally observed. Lepton-number violation (LNV) is explicitly forbidden even in the minimally extended SM, so the observation of an LNV process would be unambiguous evidence of physics beyond the SM. The search for the LNV and CLFV process μ+N(A,Z)e++N(A,Z2) (referred to as μe+) complements 0νββ decay searches, and is sensitive to potential flavor effects in the neutrino mass-generation mechanism. A theoretical motivation for μe+ is presented along with a review of the status of past μe+ experiments and future prospects. Special attention is paid to an uncertain and potentially dominant background for these searches, namely, radiative muon capture (RMC). The RMC high energy photon spectrum is theoretically understudied and existing measurements insufficiently constrain this portion of the spectrum, leading to potentially significant impacts on current and future μe+ work. Full article
(This article belongs to the Special Issue Charged Lepton Flavor Violation)
Show Figures

Figure 1

18 pages, 1037 KiB  
Article
Concurrent Effects between Geomagnetic Storms and Magnetospheric Substorms
by Tommaso Alberti, Davide Faranda, Giuseppe Consolini, Paola De Michelis, Reik V. Donner and Vincenzo Carbone
Universe 2022, 8(4), 226; https://doi.org/10.3390/universe8040226 - 6 Apr 2022
Cited by 8 | Viewed by 1790
Abstract
An accurate understanding of dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve space weather diagnosis. In this work, we exploit some recently developed methods of dynamical system theory to provide new insights and conceptual ideas in [...] Read more.
An accurate understanding of dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve space weather diagnosis. In this work, we exploit some recently developed methods of dynamical system theory to provide new insights and conceptual ideas in space weather science. In particular, we study the co-variation and recurrence statistics of two geomagnetic indices, SYM-H and AL, that measure the intensity of the globally symmetric component of the equatorial electrojet and that of the westward auroral electrojet, respectively. We find that the number of active degrees of freedom, required to describe the phase space dynamics of both indices, depends on the geomagnetic activity level. When the magnetospheric substorm activity, as monitored by the AL index, increases, the active number of degrees of freedom increases at high latitudes above the dimension obtained through classical time delay embedding methods. Conversely, a reduced number of degrees of freedom is observed during geomagnetic storms at low latitude by analysing the SYM-H index. By investigating time-dependent relations between both indices we find that a significant amount of information is shared between high and low latitude current systems originating from coupling mechanisms within the magnetosphere–ionosphere system as the result of a complex interplay between processes and phenomena of internal origin activated by the triggering of external source processes. Our observations support the idea that the near-Earth electromagnetic environment is a complex system far from an equilibrium. Full article
(This article belongs to the Section Space Science)
Show Figures

Figure 1

50 pages, 545 KiB  
Review
Introduction to Quantization of Conformal Gravity
by Lesław Rachwał
Universe 2022, 8(4), 225; https://doi.org/10.3390/universe8040225 - 6 Apr 2022
Cited by 4 | Viewed by 1720
Abstract
A method for consistent quantization of conformal gravity treating conformal symmetry in a very controllable way is presented. First, we discuss local conformal symmetry in the framework of gravitational interactions, where we view it as an example of a general gauge theory. We [...] Read more.
A method for consistent quantization of conformal gravity treating conformal symmetry in a very controllable way is presented. First, we discuss local conformal symmetry in the framework of gravitational interactions, where we view it as an example of a general gauge theory. We also present some early attempts at quantization of conformal gravity and use the generalized framework of covariant quantization due to Faddeev and Popov. Some salient issues such as the need for conformal gauge-fixing, an issue with conformal third ghosts, and discontinuities in conformal gravity are studied as well. Finally, we provide some explanations of the original ad hoc methods of computation valid at the first quantum loop level in conformal gravity. Full article
(This article belongs to the Special Issue The Quantum & The Gravity)
12 pages, 331 KiB  
Review
Scattered Radiation of Protoplanetary Disks
by Vladimir P. Grinin and Larisa V. Tambovtseva
Universe 2022, 8(4), 224; https://doi.org/10.3390/universe8040224 - 2 Apr 2022
Cited by 3 | Viewed by 1651
Abstract
Scattered radiation of circumstellar (CS) dust plays an important role in the physics of young stars. Its observational manifestations are various but more often they are connected with the appearance of intrinsic polarization in young stars and their CS disks. In our brief [...] Read more.
Scattered radiation of circumstellar (CS) dust plays an important role in the physics of young stars. Its observational manifestations are various but more often they are connected with the appearance of intrinsic polarization in young stars and their CS disks. In our brief review we consider two classes of astrophysical objects in which the participation of scattered radiation is key for understanding their nature. First of all, these are irregular variables (UX Ori type stars). The modern idea of their nature and the mechanism of their variability has been formed thanks to synchronous observations of their linear polarization and brightness. The second class of objects is the CS disks themselves. Their detailed investigation became possible due to observations in polarized light using a coronographic technique and large telescopes. Full article
(This article belongs to the Special Issue Advances in the Physics of Stars - in Memory of Prof. Yuri N. Gnedin)
Show Figures

Figure 1

15 pages, 320 KiB  
Article
The Poincaré Index and Its Applications
by Alexander G. Aleksandrov
Universe 2022, 8(4), 223; https://doi.org/10.3390/universe8040223 - 2 Apr 2022
Cited by 1 | Viewed by 5575
Abstract
We discuss an approach to the problem of calculating the local topological index of vector fields given on complex spaces or varieties with singularities developed by the author over the past few years. Our method is based on the study of the homology [...] Read more.
We discuss an approach to the problem of calculating the local topological index of vector fields given on complex spaces or varieties with singularities developed by the author over the past few years. Our method is based on the study of the homology of a contravariant version of the classical Poincaré–de Rham complex. This idea allows not only simplifying the calculations, but also clarifying the meaning of the basic constructions underlying many papers on the subject. In particular, in the graded case, the index can be expressed explicitly in terms of the elementary symmetric polynomials. We also considered some useful applications in physics, mechanics, control theory, the theory of bifurcations, etc. Full article
(This article belongs to the Special Issue Singularities in Spacetime)
11 pages, 292 KiB  
Article
From Hopf Algebra to Braided L-Algebra
by Clay James Grewcoe, Larisa Jonke, Toni Kodžoman and George Manolakos
Universe 2022, 8(4), 222; https://doi.org/10.3390/universe8040222 - 1 Apr 2022
Cited by 3 | Viewed by 1652
Abstract
We show that an L-algebra can be extended to a graded Hopf algebra with a codifferential. Then, we twist this extended L-algebra with a Drinfel’d twist, simultaneously twisting its modules. Taking the L-algebra as its own (Hopf) [...] Read more.
We show that an L-algebra can be extended to a graded Hopf algebra with a codifferential. Then, we twist this extended L-algebra with a Drinfel’d twist, simultaneously twisting its modules. Taking the L-algebra as its own (Hopf) module, we obtain the recently proposed braided L-algebra. The Hopf algebra morphisms are identified with the strict L-morphisms, whereas the braided L-morphisms define a more general L-action of twisted L-algebras. Full article
(This article belongs to the Special Issue Dualities and Geometry)
12 pages, 741 KiB  
Communication
Does the GRB Duration Depend on Redshift?
by Istvan Horvath, Istvan I. Racz, Zsolt Bagoly, Lajos G. Balázs and Sandor Pinter
Universe 2022, 8(4), 221; https://doi.org/10.3390/universe8040221 - 30 Mar 2022
Cited by 9 | Viewed by 2125
Abstract
Several hundred gamma-ray burst (GRB) redshifts have been determined to date. One of the other important properties—besides the distance—of the GRBs is the duration of the burst. In this paper, we analyse these two important quantities of the phenomena. In this paper, we [...] Read more.
Several hundred gamma-ray burst (GRB) redshifts have been determined to date. One of the other important properties—besides the distance—of the GRBs is the duration of the burst. In this paper, we analyse these two important quantities of the phenomena. In this paper, we map the two-dimensional distribution and explore some suspicious areas. As it is well known that the short GRBs are closer than the others, we search for parts in the Universe where the GRB duration is different from the others. We also analyse whether there are any ranges in the duration where the redshifts differ. We find some suspicious areas, however, no other significant region was found than the short GRB region. Full article
Show Figures

Figure 1

12 pages, 985 KiB  
Review
Insights into AGB Nucleosynthesis Thanks to Spectroscopic Abundance Measurements in Intrinsic and Extrinsic Stars
by Sophie Van Eck, Shreeya Shetye and Lionel Siess
Universe 2022, 8(4), 220; https://doi.org/10.3390/universe8040220 - 29 Mar 2022
Cited by 2 | Viewed by 1910
Abstract
The foundations of stellar nucleosynthesis have been established more than 70 years ago. Since then, much progress has been made, both on the theoretical side, with stellar evolution and nucleosynthesis models of increasing complexity, using more and more accurate nuclear data, and on [...] Read more.
The foundations of stellar nucleosynthesis have been established more than 70 years ago. Since then, much progress has been made, both on the theoretical side, with stellar evolution and nucleosynthesis models of increasing complexity, using more and more accurate nuclear data, and on the observational side, with the number of analyzed stars growing tremendously. In between, the complex machinery of abundance determination has been refined, taking into account model atmospheres of non-solar chemical composition, three-dimensional, non-LTE (non-local thermodynamic equilibrium) effects, and a growing number of atomic and molecular data. Neutron-capture nucleosynthesis processes, and in particular the s-process, have been scrutinized in various types of evolved stars, among which asymptotic giant branch stars, carbon-enhanced metal-poor stars and post-AGB stars. We review here some of the successes of the comparison between models and abundance measurements of heavy elements in stars, including in binaries, and outline some remaining unexplained features. Full article
Show Figures

Figure 1

24 pages, 2830 KiB  
Review
Technological Novelties of Ground-Based Very High Energy Gamma-Ray Astrophysics with the Imaging Atmospheric Cherenkov Telescopes
by Razmik Mirzoyan
Universe 2022, 8(4), 219; https://doi.org/10.3390/universe8040219 - 29 Mar 2022
Cited by 3 | Viewed by 2713
Abstract
In the past three decades, the ground-based technique of imaging atmospheric Cherenkov telescopes has established itself as a powerful discipline in science. Approximately 250 sources of very high gamma rays of both galactic and extra-galactic origin have been discovered largely due to this [...] Read more.
In the past three decades, the ground-based technique of imaging atmospheric Cherenkov telescopes has established itself as a powerful discipline in science. Approximately 250 sources of very high gamma rays of both galactic and extra-galactic origin have been discovered largely due to this technique. The study of these sources is providing clues to many basic questions in astrophysics, astro-particle physics, physics of cosmic rays and cosmology. The currently operational generation of telescopes offer a solid performance. Further improvements of this technique led to the next-generation large instrument known as the Cherenkov Telescope Array. In its final configuration, the sensitivity of CTA will be several times higher than that of the currently best instruments VERITAS, H.E.S.S., and MAGIC. This article is devoted to outlining the technological developments that shaped this technique and led to today’s success. Full article
Show Figures

Figure 1

Previous Issue
Next Issue
Back to TopTop