Universe

20 pages, 360 KiB

Open AccessArticle

Significance of Charge on the Dynamics of Hyperbolically Distributed Fluids

by Z. Yousaf, G. G. L. Nashed, M. Z. Bhatti and H. Asad

Universe 2022, 8(6), 337; https://doi.org/10.3390/universe8060337 - 20 Jun 2022

Cited by 6 | Viewed by 1391

This manuscript is devoted to analyze hyperbolically symmetric non-static fluid distribution incorporated with heat flux and electromagnetic field. We have developed a general framework in order to examine the dynamic regime of the matter configuration which eventually results in the static spacetime. With [...] Read more.

This manuscript is devoted to analyze hyperbolically symmetric non-static fluid distribution incorporated with heat flux and electromagnetic field. We have developed a general framework in order to examine the dynamic regime of the matter configuration which eventually results in the static spacetime. With the aim of doing this, we constructed the Einstein-Maxwell (EM) field equations and obtained the conservation equation. Furthermore, the formulation of mass function indicates the presence of the negative energy density, which leads towards the significant quantum implications. Taking into account the transport equation, we have observed the thermodynamical attributes of the fluid. Additionally, quasi- homologous constraint has been utilized to construct several models. We have deduced the worthwhile applications of the astrophysical objects by evaluating several analytical solutions in terms of the kinematical variables. Full article

(This article belongs to the Section Mathematical Physics)

3 pages, 3039 KiB

Open AccessEditorial

Editorial to the Special Issue “Quantum Cosmology”

by Paulo Vargas Moniz

Universe 2022, 8(6), 336; https://doi.org/10.3390/universe8060336 - 20 Jun 2022

Cited by 1 | Viewed by 1280

Abstract

Some time ago, when I first inquired as to ‘what quantum cosmology is about’, I did approach the hall with a combination of caution as well as eagerness [...] Full article

(This article belongs to the Special Issue Quantum Cosmology)

15 pages, 852 KiB

Open AccessReview

Ultra Long Period Cepheids: Observation and Theory

by Ilaria Musella

Universe 2022, 8(6), 335; https://doi.org/10.3390/universe8060335 - 18 Jun 2022

Cited by 7 | Viewed by 1856

Abstract

Ultra Long Period Cepheids are becoming a very interesting and important topic thanks to the contribution that they can give to understanding the current tension existing between the early-universe and local Hubble constant measurements. These bright pulsating variables are observable up to cosmological [...] Read more.

Ultra Long Period Cepheids are becoming a very interesting and important topic thanks to the contribution that they can give to understanding the current tension existing between the early-universe and local Hubble constant measurements. These bright pulsating variables are observable up to cosmological distances (larger than 100 Mpc) allowing us, in principle, to measure the Hubble constant without the need for secondary indicators, thus reducing the possible systematic errors in the calibration of the extragalactic distance scale. The Ultra Long Period Cepheids also represent a useful tool for obtaining information on the star formation history of the host galaxy and a challenge for the evolutionary and pulsational models, particularly in the very metal poor regime. In this paper, the largest known ULP sample, consisting of 72 objects, including 10 new candidates, is analyzed to give an observational and theoretical overview of their role as distance indicators and of their evolutionary properties. Full article

(This article belongs to the Special Issue Recent Advances in Pulsating Stars)

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39 pages, 523 KiB

Open AccessReview

Review on Stochastic Approach to Inflation

by Diego Cruces

Universe 2022, 8(6), 334; https://doi.org/10.3390/universe8060334 - 17 Jun 2022

Cited by 24 | Viewed by 2037

Abstract

We present a review on the state-of-the-art of the mathematical framework known as stochastic inflation, paying special attention to its derivation, and giving references for the readers interested in results coming from the application of the stochastic framework to different inflationary scenarios, especially [...] Read more.

We present a review on the state-of-the-art of the mathematical framework known as stochastic inflation, paying special attention to its derivation, and giving references for the readers interested in results coming from the application of the stochastic framework to different inflationary scenarios, especially to those of interest for primordial black hole formation. During the derivation of the stochastic formalism, we will emphasise two aspects in particular: the difference between the separate universe approach and the true long wavelength limit of scalar inhomogeneities and the generically non-Markovian nature of the noises that appear in the stochastic equations. Full article

(This article belongs to the Special Issue Primordial Black Holes from Inflation)

13 pages, 603 KiB

Open AccessArticle

Explaining the ‘Outliers’ Track in Black Hole X-ray Binaries with a BZ-Jet and Inner-Disk Coupling

by Ning Chang, Xiang Liu, Fu-Guo Xie, Lang Cui and Hao Shan

Universe 2022, 8(6), 333; https://doi.org/10.3390/universe8060333 - 17 Jun 2022

Cited by 1 | Viewed by 1868

Abstract

In this paper, we investigate the black hole (BH) spin contribution to jet power, especially for the magnetic arrested disk (MAD), where only inner accretion disk luminosity is closely coupled with the spin-jet power, and try to explain the ‘outliers’ track of the [...] Read more.

In this paper, we investigate the black hole (BH) spin contribution to jet power, especially for the magnetic arrested disk (MAD), where only inner accretion disk luminosity is closely coupled with the spin-jet power, and try to explain the ‘outliers’ track of the radio

L_{R}

to X-ray luminosity

L_{X}

in two black hole X-ray binaries (BHXBs). Our results suggest that the BZ-jet and the inner-disk coupling could account for the ‘outliers’ track of the radio/X-ray correlation in two BHXBs, H1743-322 and MAXI J1348-630. Although the accretion disk of H1743-322 in the outburst could be in the MAD state, there is a lower probability that MAXI J1348-630 is in the MAD state due to its low jet production efficiency. The difference in the inner-disk bolometric luminosity ratio of the two sources implies that these two BHXBs are in different inner-disk accretion states. We further investigate the phase-changing regime of MAXI J1348-630 and find that there is a phase transition around

L_{X} / L_{Edd} \sim 10^{- 3}

. The assumption of sub-MAD is discussed as well. Full article

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

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18 pages, 502 KiB

Open AccessArticle

Topological Gauge Actions on the Lattice as Overlap Fermion Determinants

by Nikhil Karthik and Rajamani Narayanan

Universe 2022, 8(6), 332; https://doi.org/10.3390/universe8060332 - 17 Jun 2022

Viewed by 1522

Abstract

Overlap fermion on the lattice has been shown to properly reproduce topological aspects of gauge fields. In this paper, we review the derivation of Overlap fermion formalism in a torus of three space-time dimensions. Using the formalism, we show how to use the [...] Read more.

Overlap fermion on the lattice has been shown to properly reproduce topological aspects of gauge fields. In this paper, we review the derivation of Overlap fermion formalism in a torus of three space-time dimensions. Using the formalism, we show how to use the Overlap fermion determinants in the massless and infinite mass limits to construct different continuum topological gauge actions, such as the level-k Chern–Simons action, “half-CS” term and the mixed Chern–Simons (BF) coupling, in a gauge-invariant lattice UV regulated manner. Taking special Abelian and non-Abelian background fields, we demonstrate numerically how the lattice formalism beautifully reproduces the continuum expectations, such as the flow of action under large gauge transformations. Full article

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

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15 pages, 3605 KiB

Open AccessArticle

Numerical Simulation of Ionospheric Disturbances Due to Rocket Plume and Its Influence on HF Radio Waves Propagation

by Hongwei Gong, Hanxian Fang and Zeyun Li

Universe 2022, 8(6), 331; https://doi.org/10.3390/universe8060331 - 15 Jun 2022

Cited by 1 | Viewed by 1580

Abstract

In this paper, the ionospheric disturbances of CO₂, which is released by rocket exhaust plumes, was simulated. The effect of this disturbance on the propagation of high-frequency (HF) radio waves at different incident frequencies was also simulated by using three-dimensional digital [...] Read more.

In this paper, the ionospheric disturbances of CO₂, which is released by rocket exhaust plumes, was simulated. The effect of this disturbance on the propagation of high-frequency (HF) radio waves at different incident frequencies was also simulated by using three-dimensional digital ray tracing technique. The results show that CO₂ can effectively dissipate the background electrons and form ionospheric holes after being released in the ionosphere. At the peak height of ionospheric electron density (about 300 km), the electrons are dissipated fastest and the radius of ionospheric hole is also largest. This is due to the fact that the diffusion coefficient of CO₂ usually increases with height while the electron density just increases before reaching its peak height and then decreases with height, and the chemical reaction rate between ions and CO₂ also becomes largest at the peak height of electron density (about 300 km). Around 100 s after the release of CO₂, when the radio waves at a frequency of 8 MHz pass through the ionosphere with an elevation range of 85~95°, the “secondary focusing effect” can occur, and we believe that this is due to the reflection of HF shortwaves on the walls of the ionospheric holes. With time going on, this phenomenon disappears at 300 s and only one focus is left at this time. For the HF shortwaves at same incident frequency, the focusing effect of waves displays a weakening trend with time increasing, and the height of focus center also ascends gradually. At the same time after CO₂ releasing, with the increasing of radio waves frequency, the focusing effect also becomes weaker and the focus center displays an ascending trend. Full article

(This article belongs to the Section Space Science)

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10 pages, 1998 KiB

Open AccessArticle

Modulation of Solar Wind Impact on the Earth’s Magnetosphere during the Solar Cycle

by Francesco Carbone, Daniele Telloni, Emiliya Yordanova and Luca Sorriso-Valvo

Universe 2022, 8(6), 330; https://doi.org/10.3390/universe8060330 - 14 Jun 2022

Cited by 1 | Viewed by 1773

Abstract

The understanding of extreme geomagnetic storms is one of the key issues in space weather. Such phenomena have been receiving increasing attention, especially with the aim of forecasting strong geomagnetic storms generated by high-energy solar events since they can severely perturb the near-Earth [...] Read more.

The understanding of extreme geomagnetic storms is one of the key issues in space weather. Such phenomena have been receiving increasing attention, especially with the aim of forecasting strong geomagnetic storms generated by high-energy solar events since they can severely perturb the near-Earth space environment. Here, the disturbance storm time index

D s t

, a crucial geomagnetic activity proxy for Sun–Earth interactions, is analyzed as a function of the energy carried by different solar wind streams. To determine the solar cycle activity influence on

D s t

, a 12-year dataset was split into sub-periods of maximum and minimum solar activity. Solar wind energy and geomagnetic activity were closely correlated for both periods of activity. Slow wind streams had negligible effects on Earth regardless of their energy, while high-speed streams may induce severe geomagnetic storming depending on the energy (kinetic or magnetic) carried by the flow. The difference between the two periods may be related to the higher rate of geo-effective events during the maximum activity, where coronal mass ejections represent the most energetic and geo-effective driver. During the minimum period, despite a lower rate of high energetic events, a moderate disturbance in the

D s t

index can be induced. Full article

(This article belongs to the Special Issue Advances in Solar Wind Origin and Evolution)

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15 pages, 6046 KiB

Open AccessReview

The Role of Radio Observations in Studies of Infrared-Bright Galaxies: Prospects for a Next-Generation Very Large Array

by Eric Joseph Murphy

Universe 2022, 8(6), 329; https://doi.org/10.3390/universe8060329 - 14 Jun 2022

Cited by 4 | Viewed by 1957

Abstract

The bulk of the present-day stellar mass was formed in galaxies when the universe was less than half its current age (i.e.,

1 ≲ z ≲ 3

). While this likely marks one of the most critical time periods for galaxy evolution, we [...] Read more.

The bulk of the present-day stellar mass was formed in galaxies when the universe was less than half its current age (i.e.,

1 ≲ z ≲ 3

). While this likely marks one of the most critical time periods for galaxy evolution, we currently do not have a clear picture on the radial extent and distribution of cold molecular gas and associated star formation within the disks of galaxies during this epoch. Such observations are essential to properly estimate the efficiency at which such galaxies convert their gas into stars, as well as to account for the various energetic processes that govern this efficiency. Long-wavelength (i.e., far-infrared–to–radio) observations are critical to penetrate the high-levels of extinction associated with dusty, infrared-bright galaxies that are driving the stellar mass assembly at such epochs. In this article, we discuss how the next-generation Very Large Array will take a transformative step in our understanding of galaxy formation and evolution by delivering the ability to simultaneously study the relative distributions molecular gas and star formation on sub-kpc scales unbiased by dust for large populations of typical galaxies in the early universe detected by future far-infrared space missions. Full article

(This article belongs to the Special Issue Recent Advances in Infrared Galaxies and AGN)

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23 pages, 588 KiB

Open AccessEditor’s ChoiceArticle

Onset of Electron Captures and Shallow Heating in Magnetars

by Nicolas Chamel and Anthea Francesca Fantina

Universe 2022, 8(6), 328; https://doi.org/10.3390/universe8060328 - 11 Jun 2022

Cited by 2 | Viewed by 2299

Abstract

The loss of magnetic pressure accompanying the decay of the magnetic field in a magnetar may trigger exothermic electron captures by nuclei in the shallow layers of the stellar crust. Very accurate analytical formulas are obtained for the threshold density and pressure, as [...] Read more.

The loss of magnetic pressure accompanying the decay of the magnetic field in a magnetar may trigger exothermic electron captures by nuclei in the shallow layers of the stellar crust. Very accurate analytical formulas are obtained for the threshold density and pressure, as well as for the maximum amount of heat that can be possibly released, taking into account the Landau–Rabi quantization of electron motion. These formulas are valid for arbitrary magnetic field strengths, from the weakly quantizing regime to the most extreme situation in which electrons are all confined to the lowest level. Numerical results are also presented based on experimental nuclear data supplemented with predictions from the Brussels-Montreal model HFB-24. This same nuclear model has been already employed to calculate the equation of state in all regions of magnetars. Full article

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

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15 pages, 1036 KiB

Open AccessArticle

Estimating the Transit Speed and Time of Arrival of Interplanetary Coronal Mass Ejections Using CME and Solar Flare Data

by Anatoly Belov, Nataly Shlyk, Maria Abunina, Artem Abunin and Athanasios Papaioannou

Universe 2022, 8(6), 327; https://doi.org/10.3390/universe8060327 - 11 Jun 2022

Cited by 6 | Viewed by 2164

Abstract

The dependence of Interplanetary Coronal Mass Ejections’ (ICMEs) transit speed on the corresponding Coronal Mass Ejections’ (CMEs) initial speed is investigated. It is shown that the transit speed and transit time depend not only on the CME’s initial speed, but also on the [...] Read more.

The dependence of Interplanetary Coronal Mass Ejections’ (ICMEs) transit speed on the corresponding Coronal Mass Ejections’ (CMEs) initial speed is investigated. It is shown that the transit speed and transit time depend not only on the CME’s initial speed, but also on the longitude of the solar source. The longitudinal dependence of the expected transit speeds and times are obtained from the analysis of 288 CMEs, associated with solar flares, observed from 1995 to 2020. A model, estimating the transit and maximum speeds, as well as the time of arrival of an ICME to Earth, based on the initial CME speed and the longitude of the associated solar flare has been created. It is shown that taking into account the longitude of the solar source in addition to the initial CME speed significantly improves the quality of the model, especially for events in the central part of the solar disk (E10°–W10°). The simplicity of the described model makes it accessible to a wide range of users and provides opportunities for further improvement as the statistics and the number of input parameters increase. Full article

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

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31 pages, 548 KiB

Open AccessArticle

Leading Singularities in Higher-Derivative Yang–Mills Theory and Quadratic Gravity

by Gabriel Menezes

Universe 2022, 8(6), 326; https://doi.org/10.3390/universe8060326 - 10 Jun 2022

Cited by 6 | Viewed by 1606

Abstract

In this work, we explore general leading singularities of one-loop amplitudes in higher-derivative Yang–Mills and quadratic gravity. These theories are known to possess propagators which contain quadratic and quartic momentum dependence, which leads to the presence of an unstable ghostlike resonance. However, unitarity [...] Read more.

In this work, we explore general leading singularities of one-loop amplitudes in higher-derivative Yang–Mills and quadratic gravity. These theories are known to possess propagators which contain quadratic and quartic momentum dependence, which leads to the presence of an unstable ghostlike resonance. However, unitarity cuts are not to be taken through unstable particles and therefore unitarity is still satisfied. On the other hand, this could engender issues when calculating leading singularities which are generalizations of unitarity cuts. Nevertheless, we will show with explicit examples how leading singularities are still well defined and accordingly they are able to capture relevant information on the analytic structure of amplitudes in such higher-derivative theories. We discuss some simple one-loop amplitudes which clarify these features. Full article

(This article belongs to the Special Issue Probing the Quantum Space-Time)

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10 pages, 271 KiB

Open AccessArticle

Analytic Solution and Noether Symmetries for the Hyperbolic Inflationary Model in the Jordan Frame

by Andronikos Paliathanasis

Universe 2022, 8(6), 325; https://doi.org/10.3390/universe8060325 - 10 Jun 2022

Cited by 3 | Viewed by 1492

Abstract

The Noether symmetry analysis is applied for the study of a multifield cosmological model in a spatially flat FLRW background geometry. The gravitational Action Integral consists of two scalar fields, the Brans–Dicke field and a second scalar field minimally coupled to gravity. However, [...] Read more.

The Noether symmetry analysis is applied for the study of a multifield cosmological model in a spatially flat FLRW background geometry. The gravitational Action Integral consists of two scalar fields, the Brans–Dicke field and a second scalar field minimally coupled to gravity. However, the two scalar fields interact in kinetic terms. This multifield has been found to describe the equivalent of hyperbolic inflation in the Jordan frame. The application of Noether’s theorems constrains the free parameters of the model so that conservation laws exist. We find that the field equations form an integrable dynamical system, and the analytic solution is derived. Full article

(This article belongs to the Section Cosmology)

18 pages, 3278 KiB

Open AccessArticle

Ulysses Flyby in the Heliosphere: Comparison of the Solar Wind Model with Observational Data

by Evgeniy V. Maiewski, Helmi V. Malova, Victor Yu. Popov and Lev M. Zelenyi

Universe 2022, 8(6), 324; https://doi.org/10.3390/universe8060324 - 10 Jun 2022

Cited by 2 | Viewed by 2296

Abstract

A model capable of reproducing a set of solar wind parameters along the virtual spacecraft orbit out of an ecliptic plane has been developed. In the framework of a quasi-stationary axisymmetric self-consistent MHD model the spatial distributions of magnetic field and plasma characteristics [...] Read more.

A model capable of reproducing a set of solar wind parameters along the virtual spacecraft orbit out of an ecliptic plane has been developed. In the framework of a quasi-stationary axisymmetric self-consistent MHD model the spatial distributions of magnetic field and plasma characteristics at distances from 20 to 1200 Solar radii at almost all solar latitudes could be obtained and analyzed. This model takes into account the Sun’s magnetic field evolution during the solar cycle, when the dominant dipole magnetic field is replaced by the quadrupole one. Self-consistent solutions for solar wind characteristics were obtained, depending on the phase of the solar cycle. To verify the model, its results are compared with the observed characteristics of solar wind along the Ulysses trajectory during its flyby around the Sun from 1990 to 2009. It is shown that the results of numerical simulation are generally consistent with the observational data obtained by the Ulysses spacecraft. A comparison of the model and experimental data confirms that the model can adequately describe the solar wind parameters and can be used for heliospheric studies at different phases of the solar activity cycle, as well as in a wide range of latitudinal angles and distances to the Sun. Full article

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

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31 pages, 464 KiB

Open AccessEditor’s ChoiceReview

Lorentz Symmetry Violation of Cosmic Photons

by Ping He and Bo-Qiang Ma

Universe 2022, 8(6), 323; https://doi.org/10.3390/universe8060323 - 9 Jun 2022

Cited by 23 | Viewed by 2988

Abstract

As a basic symmetry of space-time, Lorentz symmetry has played important roles in various fields of physics, and it is a glamorous question whether Lorentz symmetry breaks. Since Einstein proposed special relativity, Lorentz symmetry has withstood very strict tests, but there are still [...] Read more.

As a basic symmetry of space-time, Lorentz symmetry has played important roles in various fields of physics, and it is a glamorous question whether Lorentz symmetry breaks. Since Einstein proposed special relativity, Lorentz symmetry has withstood very strict tests, but there are still motivations for Lorentz symmetry violation (LV) research from both theoretical consideration and experimental feasibility, that attract physicists to work on LV theories, phenomena and experimental tests with enthusiasm. There are many theoretical models including LV effects, and different theoretical models predict different LV phenomena, from which we can verify or constrain LV effects. Here, we introduce three types of LV theories: quantum gravity theory, space-time structure theory and effective field theory with extra-terms. Limited by the energy of particles, the experimental tests of LV are very difficult; however, due to the high energy and long propagation distance, high-energy particles from astronomical sources can be used for LV phenomenological researches. Especially with cosmic photons, various astronomical observations provide rich data from which one can obtain various constraints for LV researches. Here, we review four common astronomical phenomena which are ideal for LV studies, together with current constraints on LV effects of photons. Full article

(This article belongs to the Special Issue Ultra High Energy Photons)

24 pages, 482 KiB

Open AccessArticle

The Macro-Physics of the Quark-Nova: Astrophysical Implications

by Rachid Ouyed

Universe 2022, 8(6), 322; https://doi.org/10.3390/universe8060322 - 9 Jun 2022

Cited by 4 | Viewed by 1947

Abstract

A quark-nova is a hypothetical stellar evolution branch where a neutron star converts explosively into a quark star. Here, we discuss the intimate coupling between the micro-physics and macro-physics of the quark-nova and provide a prescription for how to couple the Burn-UD code [...] Read more.

A quark-nova is a hypothetical stellar evolution branch where a neutron star converts explosively into a quark star. Here, we discuss the intimate coupling between the micro-physics and macro-physics of the quark-nova and provide a prescription for how to couple the Burn-UD code to the stellar evolution code in order to simulate neutron-star-to-quark-star burning at stellar scales and estimate the resulting energy release and ejecta. Once formed, the thermal evolution of the proto-quark star follows. We found much higher peak neutrino luminosities (>10

^{55}

erg/s) and a higher energy neutrino (i.e., harder) spectrum than previous stellar evolution studies of proto-neutron stars. We derived the neutrino counts that observatories such as Super-Kamiokande-III and Halo-II should expect and suggest how these can differentiate between a supernova and a quark-nova. Due to the high peak neutrino luminosities, neutrino pair annihilation can deposit as much as

10^{52}

ergs in kinetic energy in the matter overlaying the neutrinosphere, yielding relativistic quark-nova ejecta. We show how the quark-nova could help us understand many still enigmatic high-energy astrophysical transients, such as super-luminous supernovae, gamma-ray bursts and fast radio bursts. Full article

(This article belongs to the Special Issue Properties and Dynamics of Neutron Stars and Proto-Neutron Stars)

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15 pages, 352 KiB

Open AccessReview

Testing Quantum Gravity in the Multi-Messenger Astronomy Era

by Aleksandra Piórkowska-Kurpas and Marek Biesiada

Universe 2022, 8(6), 321; https://doi.org/10.3390/universe8060321 - 8 Jun 2022

Cited by 2 | Viewed by 1986

Abstract

Quantum gravity (QG) remains elusive despite almost century-long efforts to combine general relativity and quantum mechanics. All the approaches triggered and powered by purely theoretical considerations eventually failed with a prevailing feeling of a complete lack of guidance from the experimental side. Currently, [...] Read more.

Quantum gravity (QG) remains elusive despite almost century-long efforts to combine general relativity and quantum mechanics. All the approaches triggered and powered by purely theoretical considerations eventually failed with a prevailing feeling of a complete lack of guidance from the experimental side. Currently, however, this circumstance is beginning to change considerably. We have entered the era of multi-messenger astronomy. The electromagnetic window to the universe—so far the only one—has been tremendously enlarged in the energy range beyond gamma rays up to ultra-high-energy photons and has been complemented by other messengers: high-energy cosmic rays, cosmic neutrinos, and gravitational waves (GWs). This has created a unique environment in which to observationally constrain various phenomenological QG effects. In this paper, we focus on the LIV phenomenology manifested as energy-dependent time-of-flight delays and strong lensing time delays. We review results regarding time-of-flight delays obtained with GRBs. We also recall the idea of energy-dependent lensing time delays, which allow one to constrain LIV models independently of the intrinsic time delay. Lastly, we show how strongly a gravitationally lensed GW signal would place interesting constraints on the LIV. Full article

(This article belongs to the Special Issue Ultra High Energy Photons)

12 pages, 3691 KiB

Open AccessArticle

Chaos in a Magnetized Modified Gravity Schwarzschild Spacetime

by Daqi Yang, Wenfu Cao, Naying Zhou, Hongxing Zhang, Wenfang Liu and Xin Wu

Universe 2022, 8(6), 320; https://doi.org/10.3390/universe8060320 - 8 Jun 2022

Cited by 17 | Viewed by 1843

Abstract

Based on the scalar–tensor–vector modified gravitational theory, a modified gravity Schwarzschild black hole solution has been given in the existing literature. Such a black hole spacetime is obtained through the inclusion of a modified gravity coupling parameter, which corresponds to the modified gravitational [...] Read more.

Based on the scalar–tensor–vector modified gravitational theory, a modified gravity Schwarzschild black hole solution has been given in the existing literature. Such a black hole spacetime is obtained through the inclusion of a modified gravity coupling parameter, which corresponds to the modified gravitational constant and the black hole charge. In this sense, the modified gravity parameter acts as not only an enhanced gravitational effect but also a gravitational repulsive force contribution to a test particle moving around the black hole. Because the modified Schwarzschild spacetime is static spherical symmetric, it is integrable. However, the spherical symmetry and the integrability are destroyed when the black hole is immersed in an external asymptotic uniform magnetic field and the particle is charged. Although the magnetized modified Schwarzschild spacetime is nonintegrable and inseparable, it allows for the application of explicit symplectic integrators when its Hamiltonian is split into five explicitly integrable parts. Taking one of the proposed explicit symplectic integrators and the techniques of Poincaré sections and fast Lyapunov indicators as numerical tools, we show that the charged particle can have chaotic motions under some circumstances. Chaos is strengthened with an increase of the modified gravity parameter from the global phase space structures. There are similar results when the magnetic field parameter and the particle energy increase. However, an increase of the particle angular momentum weakens the strength of chaos. Full article

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

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18 pages, 720 KiB

Open AccessReview

Maximal Kinematical Invariance Group of Fluid Dynamics and Applications

by V. V. Sreedhar and Amitabh Virmani

Universe 2022, 8(6), 319; https://doi.org/10.3390/universe8060319 - 7 Jun 2022

Cited by 2 | Viewed by 1596

Abstract

The maximal kinematical invariance group of the Euler equations of fluid dynamics for the standard polytropic exponent is larger than the Galilei group. Specifically, the inversion transformation [...] Read more.

The maximal kinematical invariance group of the Euler equations of fluid dynamics for the standard polytropic exponent is larger than the Galilei group. Specifically, the inversion transformation

(Σ : t \to - 1 / t, \vec{x} \to \vec{x} / t)

leaves the Euler equation’s invariant. This duality has been used to explain the striking similarities observed in simulations of the supernova explosions and laboratory implosions induced in plasma by intense lasers. The inversion symmetry extends to discontinuous fluid flows as well. In this contribution, we provide a concise review of these ideas and discuss some applications. We also explicitly work out the implosion dual of the Sedov’s explosion solution. Full article

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

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48 pages, 622 KiB

Open AccessReview

Covariant Evolution of Gravitoelectromagnetism

by Ashkbiz Danehkar

Universe 2022, 8(6), 318; https://doi.org/10.3390/universe8060318 - 7 Jun 2022

Cited by 2 | Viewed by 2075

Abstract

The long-range gravitational terms associated with tidal forces, frame-dragging effects, and gravitational waves are described by the Weyl conformal tensor, the traceless part of the Riemann curvature that is not locally affected by the matter field. The Ricci and Bianchi identities provide a [...] Read more.

The long-range gravitational terms associated with tidal forces, frame-dragging effects, and gravitational waves are described by the Weyl conformal tensor, the traceless part of the Riemann curvature that is not locally affected by the matter field. The Ricci and Bianchi identities provide a set of dynamical and kinematic equations governing the matter coupling and evolution of the electric and magnetic parts of the Weyl tensor, so-called gravitoelectric and gravitomagnetic fields. A detailed analysis of the Weyl gravitoelectromagnetic fields can be conducted using a number of algebraic and differential identities prescribed by the

1 + 3

covariant formalism. In this review, we consider the dynamical constraints and propagation equations of the gravitoelectric/-magnetic fields and covariantly debate their analytic properties. We discuss the special conditions under which gravitational waves can propagate, the inconsistency of a Newtonian-like model without gravitomagnetism, the nonlinear generalization to multi-fluid models with different matter species, as well as observational effects caused by the Weyl fields via the kinematic quantities. The

1 + 3

tetrad and

1 + 1 + 2

semi-covariant methods, which can equally be used for gravitoelectromagnetism, are briefly explained, along with their correspondence with the covariant formulations. Full article

(This article belongs to the Special Issue Frame-Dragging and Gravitomagnetism)

11 pages, 444 KiB

Open AccessArticle

Constraints on the Helium Abundance from Fast Radio Bursts

by Liang Jing and Jun-Qing Xia

Universe 2022, 8(6), 317; https://doi.org/10.3390/universe8060317 - 5 Jun 2022

Cited by 3 | Viewed by 1661

Abstract

Through the relationship between dispersion measures (DM) and redshifts, fast radio bursts (FRBs) are considered to be very promising cosmological probes. In this paper, we attempted to use the DM-z relationship of FRBs to study the helium abundance (

Y_{He}

) in [...] Read more.

Through the relationship between dispersion measures (DM) and redshifts, fast radio bursts (FRBs) are considered to be very promising cosmological probes. In this paper, we attempted to use the DM-z relationship of FRBs to study the helium abundance (

Y_{He}

) in the universe. First, we used 17 current FRBs with known redshifts for our study. Due to their low redshifts and the strong degeneracy between

Y_{He}

and

Ω_{b} h^{2}

, however, this catalog could not provide a good constraint on the helium abundance. Then, we simulated 500 low redshift FRB mock data with

z \in [0, 1.5]

to forecast the constraining ability on

Y_{He}

. In order to break the degeneracy between

Y_{He}

and

Ω_{b} h^{2}

further, we introduced the shift parameters of the Planck measurement

(R, l_{A}, Ω_{b} h^{2})

as a prior, where

Ω_{b} h^{2}

represents the baryon density parameter, and R and

l_{A}

correspond to the scaled distance to recombination and the angular scale of the sound horizon at recombination, respectively. We obtained the standard deviation for the helium abundance:

σ (Y_{He}) = 0.025

. Finally, we considered 2000 higher redshift FRB data with the redshift distribution of

[0, 3]

and found that the constraining power for

Y_{He}

would be improved by more than 2 times,

σ (Y_{He}) = 0.011

, which indicates that the FRB data with high redshift can provide a better constraint on the helium abundance. Hopefully, large FRB samples with high redshift from the Square Kilometre Array can provide high-precision measurements of the helium abundance in the near future. Full article

(This article belongs to the Section Cosmology)

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20 pages, 1950 KiB

Open AccessReview

Shape Invariant Potentials in Supersymmetric Quantum Cosmology

by Shahram Jalalzadeh, Seyed Meraj M. Rasouli and Paulo Moniz

Universe 2022, 8(6), 316; https://doi.org/10.3390/universe8060316 - 5 Jun 2022

Cited by 6 | Viewed by 2245

Abstract

In this brief review, we comment on the concept of shape invariant potentials, which is an essential feature in many settings of

N = 2

supersymmetric quantum mechanics. To motivate its application within supersymmetric quantum cosmology, we present a case study to illustrate [...] Read more.

In this brief review, we comment on the concept of shape invariant potentials, which is an essential feature in many settings of

N = 2

supersymmetric quantum mechanics. To motivate its application within supersymmetric quantum cosmology, we present a case study to illustrate the value of this promising tool. Concretely, we take a spatially flat FRW model in the presence of a single scalar field, minimally coupled to gravity. Then, we extract the associated Schrödinger–Wheeler–DeWitt equation, allowing for a particular scope of factor ordering. Subsequently, we compute the corresponding supersymmetric partner Hamiltonians,

H_{1}

and

H_{2}

. Moreover, we point out how the shape invariance property can be employed to bring a relation among several factor orderings choices for our Schrödinger–Wheeler–DeWitt equation. The ground state is retrieved, and the excited states easily written. Finally, the Hamiltonians,

H_{1}

and

H_{2}

, are explicitly presented within a

N = 2

supersymmetric quantum mechanics framework. Full article

(This article belongs to the Special Issue Quantum Cosmology)

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23 pages, 399 KiB

Open AccessArticle

Superposition Principle and Kirchhoff’s Integral Theorem

by Mikhail I. Krivoruchenko

Universe 2022, 8(6), 315; https://doi.org/10.3390/universe8060315 - 3 Jun 2022

Cited by 2 | Viewed by 2096

Abstract

The need for modification of the Huygens–Fresnel superposition principle arises even in the description of the free fields of massive particles and, more extensively, in nonlinear field theories. A wide range of formulations and superposition schemes for secondary waves are captured by Kirchhoff’s [...] Read more.

The need for modification of the Huygens–Fresnel superposition principle arises even in the description of the free fields of massive particles and, more extensively, in nonlinear field theories. A wide range of formulations and superposition schemes for secondary waves are captured by Kirchhoff’s integral theorem. We discuss various versions of this theorem as well as its connection with the superposition principle and the method of Green’s functions. A superposition scheme inherent in linear field theories, which is not based on Kirchhoff’s integral theorem but instead relies on the completeness condition, is also discussed. Full article

(This article belongs to the Special Issue Selected Topics in Gravity, Field Theory and Quantum Mechanics)

29 pages, 3133 KiB

Open AccessArticle

ALPINE: A Large Survey to Understand Teenage Galaxies

by Andreas L. Faisst, Lin Yan, Matthieu Béthermin, Paolo Cassata, Miroslava Dessauges-Zavadsky, Yoshinobu Fudamoto, Michele Ginolfi, Carlotta Gruppioni, Gareth Jones, Yana Khusanova, Olivier LeFèvre, Francesca Pozzi, Michael Romano, John Silverman and Brittany Vanderhoof

Universe 2022, 8(6), 314; https://doi.org/10.3390/universe8060314 - 1 Jun 2022

Cited by 5 | Viewed by 2717

Abstract

A multiwavelength study of galaxies is important to understand their formation and evolution. Only in the recent past, thanks to the Atacama Large (Sub) Millimeter Array (ALMA), were we able to study the far-infrared (IR) properties of galaxies at high redshifts. In this [...] Read more.

A multiwavelength study of galaxies is important to understand their formation and evolution. Only in the recent past, thanks to the Atacama Large (Sub) Millimeter Array (ALMA), were we able to study the far-infrared (IR) properties of galaxies at high redshifts. In this article, we summarize recent research highlights and their significance to our understanding of early galaxy evolution from the ALPINE survey, a large program with ALMA to observe the dust continuum and

158 μ m

C

^{+}

emission of normal star-forming galaxies at

z =

4–6. Combined with ancillary data at UV through near-IR wavelengths, ALPINE provides the currently largest multiwavelength sample of post-reionization galaxies and has advanced our understanding of (i) the demographics of C

^{+}

emission; (ii) the relation of star formation and C

^{+}

emission; (iii) the gas content; (iv) outflows and enrichment of the intergalactic medium; and (v) the kinematics, emergence of disks, and merger rates in galaxies at

z > 4

. ALPINE builds the basis for more detailed measurements with the next generation of telescopes, and places itself as an important post-reionization baseline sample to allow a continuous study of galaxies over 13 billion years of cosmic time. Full article

(This article belongs to the Special Issue Recent Advances in Infrared Galaxies and AGN)

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21 pages, 410 KiB

Open AccessArticle

Antistars or Antimatter Cores in Mirror Neutron Stars?

by Zurab Berezhiani

Universe 2022, 8(6), 313; https://doi.org/10.3390/universe8060313 - 31 May 2022

Cited by 11 | Viewed by 2100

Abstract

The oscillation of the neutron n into mirror neutron

n^{'}

, its partner from the dark mirror sector, can gradually transform an ordinary neutron star into a mixed star consisting in part of mirror dark matter. The implications of the reverse process [...] Read more.

The oscillation of the neutron n into mirror neutron

n^{'}

, its partner from the dark mirror sector, can gradually transform an ordinary neutron star into a mixed star consisting in part of mirror dark matter. The implications of the reverse process taking place in the mirror neutron stars depend on the sign of baryon asymmetry in the mirror sector. Namely, if it is negative, as predicted by certain baryogenesis scenarios, then

\bar{n^{'}} - \bar{n}

transitions create a core of our antimatter gravitationally trapped in the mirror star interior. The annihilation of accreted gas on such antimatter cores could explain the origin of

γ

-source candidates with an unusual spectrum compatible with baryon–antibaryon annihilation, recently identified in the Fermi LAT catalog. In addition, some part of this antimatter escaping after the mergers of mirror neutron stars can produce the flux of cosmic antihelium and also heavier antinuclei which are hunted in the AMS-02 experiment. Full article

(This article belongs to the Special Issue Focus on Dark Matter)

10 pages, 260 KiB

Open AccessArticle

Solving Linear Tensor Equations II: Including Parity Odd Terms in Four Dimensions

by Damianos Iosifidis

Universe 2022, 8(6), 312; https://doi.org/10.3390/universe8060312 - 31 May 2022

Cited by 3 | Viewed by 1312

Abstract

In this paper, focusing on 4-dimensional space, we extend our previous results of solving linear tensor equations. In particular, we consider a 30-parameter linear tensor equation for the unknown tensor component

N_{α μ ν}

in terms of the known component (source) [...] Read more.

In this paper, focusing on 4-dimensional space, we extend our previous results of solving linear tensor equations. In particular, we consider a 30-parameter linear tensor equation for the unknown tensor component

N_{α μ ν}

in terms of the known component (source)

B_{α μ ν}

. The extension also included the parity even linear terms in

N_{α μ ν}

(and the associated traces), which are formed by contracting the latter with the 4-dimensional Levi-Civita pseudotensor. Assuming generic non-degeneracy conditions and following a step-by-step procedure, we show how to explicitly solve for the unknown tensor field component

N_{α μ ν}

and, consequently, derive its unique and exact solution in terms of the component

B_{α μ ν}

. Full article

(This article belongs to the Section Mathematical Physics)

10 pages, 390 KiB

Open AccessArticle

Many-Quark Interactions: Large-N Scaling and Contribution to Baryon Masses

by Fabien Buisseret, Cintia T. Willemyns and Claude Semay

Universe 2022, 8(6), 311; https://doi.org/10.3390/universe8060311 - 31 May 2022

Cited by 5 | Viewed by 1566

Abstract

Starting from an effective Hamiltonian modeling, of a baryon made of N identical quarks in the large-N approach of QCD, we obtain analytical formulas, allowing to estimate the contributions of multiquark interactions to the baryon mass. The cases of vanishing (mass spectrum) [...] Read more.

Starting from an effective Hamiltonian modeling, of a baryon made of N identical quarks in the large-N approach of QCD, we obtain analytical formulas, allowing to estimate the contributions of multiquark interactions to the baryon mass. The cases of vanishing (mass spectrum) and non-vanishing (baryon melting) temperatures are treated. Full article

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

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30 pages, 4326 KiB

Open AccessReview

GRB Prompt Emission: Observed Correlations and Their Interpretations

by Tyler Parsotan and Hirotaka Ito

Universe 2022, 8(6), 310; https://doi.org/10.3390/universe8060310 - 31 May 2022

Cited by 15 | Viewed by 2550

Abstract

The prompt emission of Gamma Ray Bursts (GRBs) is still an outstanding question in the study of these cataclysmic events. Part of what makes GRBs difficult to study is how unique each event seems to be. However, aggregating many GRB observations and analyzing [...] Read more.

The prompt emission of Gamma Ray Bursts (GRBs) is still an outstanding question in the study of these cataclysmic events. Part of what makes GRBs difficult to study is how unique each event seems to be. However, aggregating many GRB observations and analyzing the population allows us to obtain a better understanding of the emission mechanism that produces the observed prompt emission. In this review, we outline some of the most prevalent correlations that have emerged from GRB prompt emission observations and how these correlations are interpreted in relation to physical properties and prompt emission models of GRB. Full article

(This article belongs to the Special Issue GRBs Phenomenology, Models and Applications: A Beginner Guide)

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10 pages, 730 KiB

Open AccessArticle

Shell Model Description of Spin-Dependent Elastic and Inelastic WIMP Scattering off ¹¹⁹Sn and ¹²¹Sb

by Joona Kasurinen, Jouni Suhonen, Praveen C. Srivastava and Pekka Pirinen

Universe 2022, 8(6), 309; https://doi.org/10.3390/universe8060309 - 31 May 2022

Viewed by 2271

Abstract

In this work, we calculate the spin structure functions for spin-dependent elastic and inelastic WIMP scattering off

^{119}

Sn and

^{121}

Sb. Estimates for detection rates are also given.

^{119}

Sn and

^{121}

Sb are amenable to nuclear structure calculations using the nuclear [...] Read more.

In this work, we calculate the spin structure functions for spin-dependent elastic and inelastic WIMP scattering off

^{119}

Sn and

^{121}

Sb. Estimates for detection rates are also given.

^{119}

Sn and

^{121}

Sb are amenable to nuclear structure calculations using the nuclear shell model (NSM). With the possible exception of

^{201}

Hg, they are the only such nuclei still unexplored theoretically for their potential of inelastic WIMP scattering to a very low excited state. The present calculations were conducted using a state-of-the-art WIMP–nucleus scattering formalism, and the available effective NSM two-body interactions describe the spectroscopic properties of these nuclei reasonably well. Structure functions were found to be high for both nuclei in the case of elastic scattering. Elastic scattering dominated at the zero momentum transfer limit. Detection rate calculations indicated that inelastic scattering was relevant for both nuclei, even surpassing elastic rates for some recoil energies. Full article

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5 pages, 252 KiB

Open AccessCommunication

A Note on Proton Stability in the Standard Model

by Seth Koren

Universe 2022, 8(6), 308; https://doi.org/10.3390/universe8060308 - 30 May 2022

Cited by 6 | Viewed by 1611

Abstract

In this short note, we describe the symmetry responsible for absolute, nonperturbative proton stability in the Standard Model. The SM with

N_{c}

colors and

N_{g}

generations has an exact, anomaly-free, generation-independent, global symmetry group [...] Read more.

In this short note, we describe the symmetry responsible for absolute, nonperturbative proton stability in the Standard Model. The SM with

N_{c}

colors and

N_{g}

generations has an exact, anomaly-free, generation-independent, global symmetry group

U {(1)}_{B - N_{c} L} \times Z_{N_{g}}^{L}

, which contains a subgroup of baryon plus lepton number of order

2 N_{c} N_{g}

. This disallows proton decay for

N_{g} > 1

. Many well-studied models beyond the SM explicitly break this global symmetry, and the alternative deserves further attention. Full article

(This article belongs to the Special Issue Dark Matter and Dark Energy: Particle Physics, Cosmology, and Experimental Searches)

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