Universe

18 pages, 656 KiB

Open AccessArticle

Einstein-AdS Gravity Coupled to Nonlinear Electrodynamics, Magnetic Black Holes, Thermodynamics in an Extended Phase Space and Joule–Thomson Expansion

by Sergey Il’ich Kruglov

Universe 2023, 9(10), 456; https://doi.org/10.3390/universe9100456 - 23 Oct 2023

Viewed by 1068

Abstract

We studied Einstein’s gravity with negative cosmological constant coupled to nonlinear electrodynamics proposed earlier. The metric and mass functions and corrections to the Reissner–Nordström solution are obtained. Black hole solutions can have one or two horizons. Thermodynamics and phase transitions of magnetically charged [...] Read more.

We studied Einstein’s gravity with negative cosmological constant coupled to nonlinear electrodynamics proposed earlier. The metric and mass functions and corrections to the Reissner–Nordström solution are obtained. Black hole solutions can have one or two horizons. Thermodynamics and phase transitions of magnetically charged black holes in Anti-de Sitter spacetime are investigated. The first law of black hole thermodynamics is formulated and the generalized Smarr relation is proofed. By calculating the Gibbs free energy and heat capacity we study the black hole stability. Zero-order (reentrant), first-order, and second-order phase transitions are analyzed. The Joule–Thomson expansion is considered, showing the cooling and heating phase transitions. It was shown that the principles of causality and unitarity are satisfied in the model under consideration. Full article

(This article belongs to the Section Gravitation)

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16 pages, 3070 KiB

Open AccessReview

Transiting Circumbinary Planets in the Era of Space-Based Photometric Surveys

by Veselin B. Kostov

Universe 2023, 9(10), 455; https://doi.org/10.3390/universe9100455 - 21 Oct 2023

Viewed by 1153

Abstract

Planets orbiting binary stars—circumbinary planets—play a paramount role in our understanding of planetary and stellar formation and evolution, dynamical interactions in many-body systems, and the potential for habitable environments beyond the Solar System. Each new discovery holds immense value and inherent fascination both [...] Read more.

Planets orbiting binary stars—circumbinary planets—play a paramount role in our understanding of planetary and stellar formation and evolution, dynamical interactions in many-body systems, and the potential for habitable environments beyond the Solar System. Each new discovery holds immense value and inherent fascination both for the astronomical community and for the general public. This is perhaps best demonstrated by the 1500+ citations of the discovery papers for the 14 known transiting circumbinary planets and the dozens of related press-releases in major news outlets. This article reviews the observational and theoretical aspects related to the detection and confirmation of transiting circumbinary planets around main-sequence binaries from space-based surveys, discusses the associated challenges, and highlights some of the recent results. Full article

(This article belongs to the Special Issue The Royal Road: Eclipsing Binaries and Transiting Exoplanets)

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14 pages, 332 KiB

Open AccessArticle

Teleparallel Robertson-Walker Geometries and Applications

by Alan Albert Coley, Alexandre Landry and Fateme Gholami

Universe 2023, 9(10), 454; https://doi.org/10.3390/universe9100454 - 21 Oct 2023

Cited by 1 | Viewed by 1074

Abstract

In teleparallel geometries, the coframe and corresponding spin connection are the principal geometric objects and, consequently, the appropriate definition of a symmetry is that of an affine symmetry. The set of invariant coframes and their corresponding spin connections that respect the full six [...] Read more.

In teleparallel geometries, the coframe and corresponding spin connection are the principal geometric objects and, consequently, the appropriate definition of a symmetry is that of an affine symmetry. The set of invariant coframes and their corresponding spin connections that respect the full six dimensional Lie algebra of Robertson–Walker affine symmetries are displayed and discussed. We will refer to such geometries as teleparallel Robertson–Walker (TRW) geometries, where the corresponding derived metric is of Robertson–Walker form and is characterized by the parameter

k = (- 1, 0, 1)

. The field equations are explicitly presented for the

F (T)

class of teleparallel TRW spacetimes. We are primarily interested in investigating the

k \neq 0

TRW models. After first studying the

k = 0

models and, in particular, writing their governing field equations in an appropriate form, we then study their late time stability with respect to perturbations in k in both the cases of a vanishing and non-vanishing effective cosmological constant term. As an illustration, we consider both quadratic

F (T)

theories and power-law solutions. Full article

(This article belongs to the Special Issue Mathematical Cosmology)

11 pages, 288 KiB

Open AccessArticle

Anisotropic Universes Sourced by Modified Chaplygin Gas

by Saibal Ray, Sunil Kumar Tripathy, Rikpratik Sengupta, Bibhudutta Bal and Sonali Monalisa Rout

Universe 2023, 9(10), 453; https://doi.org/10.3390/universe9100453 - 20 Oct 2023

Viewed by 996

Abstract

In this work, we perform a comparative study of the Kantowski–Sachs (KS) and Bianchi-I anisotropic universes with Modified Chaplygin gas (MCG) as matter source. We obtain the volume and scale factors as solutions to the Einstein Field Equations (EFEs) for the anisotropic universes, [...] Read more.

In this work, we perform a comparative study of the Kantowski–Sachs (KS) and Bianchi-I anisotropic universes with Modified Chaplygin gas (MCG) as matter source. We obtain the volume and scale factors as solutions to the Einstein Field Equations (EFEs) for the anisotropic universes, and check whether the initial anisotropy is washed out or not for different values of the MCG parameters present in the solution by obtaining the anisotropy parameters for each solution. The deceleration parameter is also obtained for each solution, the significance of which is discussed in the concluding section. Interestingly there are a number of notable results that appear from our study which help us to compare and contrast the two different anisotropic models along with proper understanding of the role of MCG as matter source in these models. Full article

(This article belongs to the Section Cosmology)

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13 pages, 287 KiB

Open AccessArticle

Defect Wormholes Are Defective

by Joshua Baines, Rudeep Gaur and Matt Visser

Universe 2023, 9(10), 452; https://doi.org/10.3390/universe9100452 - 17 Oct 2023

Cited by 2 | Viewed by 1025

Abstract

The various “defect wormholes” developed by Klinkhamer have recently attracted considerable attention—especially in view of the fact that the simplest example, the so-called “vacuum defect wormhole”, was claimed to be an everywhere-vacuum everywhere-Ricci-flat exact solution to the Einstein equations. This claim has been [...] Read more.

The various “defect wormholes” developed by Klinkhamer have recently attracted considerable attention—especially in view of the fact that the simplest example, the so-called “vacuum defect wormhole”, was claimed to be an everywhere-vacuum everywhere-Ricci-flat exact solution to the Einstein equations. This claim has been conclusively refuted by Feng, and in the current article, we take a deeper look at exactly what goes wrong. The central issue is this: Although Klinkhamer’s specific representation of the metric

g_{a b}

is smooth (

C^{\infty}

), his inverse metric

g^{a b}

is not even everywhere continuous (

C^{0}

), being undefined at the wormhole throat. This situation implies that one should very carefully investigate curvature tensors at the throat using the Israel–Lanczos–Sen thin-shell formalism. Doing so reveals the presence of a delta-function energy-condition-violating thin shell of matter at the wormhole throat. The “defect wormholes” are thus revealed to be quite ordinary “cut-and-paste” thin-shell wormholes, but represented in a coordinate system that is unfortunately pathological at exactly the same place that all the interesting physics occurs. To help clarify the situation, we shall focus on the behavior of suitable coordinate invariants—the Ricci scalar, the eigenvalues of the mixed

R^{a}_{b}

Ricci tensor, and the eigenvalues of the mixed

R^{a b}_{c d}

Riemann tensor. Full article

(This article belongs to the Section Gravitation)

12 pages, 290 KiB

Open AccessEditor’s ChoiceArticle

A New Approach to String Theory

by Albert Schwarz

Universe 2023, 9(10), 451; https://doi.org/10.3390/universe9100451 - 16 Oct 2023

Cited by 2 | Viewed by 1027

Abstract

In the present paper, we consider quantum theories obtained through the quantization of classical theories with first-class constraints assuming that these constraints form a Lie algebra. We show that in this case, one can construct physical quantities of a new type. We apply [...] Read more.

In the present paper, we consider quantum theories obtained through the quantization of classical theories with first-class constraints assuming that these constraints form a Lie algebra. We show that in this case, one can construct physical quantities of a new type. We apply this construction to string theory. We find that scattering amplitudes in critical bosonic closed string theory can be expressed in terms of physical quantities of the new type. Our techniques can also be applied to superstrings and heterotic strings. Full article

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

15 pages, 1065 KiB

Open AccessArticle

New Localization Method of Abelian Gauge Fields on Bloch Branes

by Yi Zhong and Yun-Zhi Du

Universe 2023, 9(10), 450; https://doi.org/10.3390/universe9100450 - 16 Oct 2023

Viewed by 1138

Abstract

In this paper, we study the localization of the five-dimensional

U (1)

gauge field coupled with a background scalar potential on symmetric and asymmetric degenerate Bloch branes. By decomposing the

U (1)

gauge field

A_{M}

into its vector [...] Read more.

In this paper, we study the localization of the five-dimensional

U (1)

gauge field coupled with a background scalar potential on symmetric and asymmetric degenerate Bloch branes. By decomposing the

U (1)

gauge field

A_{M}

into its vector part (

{\hat{A}}_{M}

) and scalar components, we found that the Lagrangian of the five-dimensional

U (1)

gauge field can be rewritten as two independent parts: one for the vector field and the other for two scalar fields. Regarding the vector part, the effective potential exhibits a volcano-like shape with finite depth. We obtain a massless vector field on both types of Bloch branes and a set of massive KK resonances. For the scalar part, their massless modes are coupled with each other, while two sets of massive scalar KK modes are independent. Similar to the vector effective potential, the scalar potentials create infinite wells for both types of degenerate Bloch brane solutions. Therefore, there is only one independent massless scalar mode and two sets of massive scalar Kaluza–Klein resonances. Furthermore, we also observed that, for the two types of Bloch brane solutions, the asymmetric parameter

c_{0}

has different effects on the localization of scalar modes. Full article

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

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20 pages, 873 KiB

Open AccessReview

Neutron Dark Decay

by Bartosz Fornal

Universe 2023, 9(10), 449; https://doi.org/10.3390/universe9100449 - 16 Oct 2023

Cited by 5 | Viewed by 1382

Abstract

There exists a puzzling disagreement between the results for the neutron lifetime obtained in experiments using the beam technique versus those relying on the bottle method. A possible explanation of this discrepancy postulates the existence of a beyond-Standard-Model decay channel of the neutron [...] Read more.

There exists a puzzling disagreement between the results for the neutron lifetime obtained in experiments using the beam technique versus those relying on the bottle method. A possible explanation of this discrepancy postulates the existence of a beyond-Standard-Model decay channel of the neutron involving new particles in the final state, some of which can be dark matter candidates. We review the current theoretical status of this proposal and discuss the particle physics models accommodating such a dark decay. We then elaborate on the efforts undertaken to test this hypothesis, summarizing the prospects for probing neutron dark decay channels in future experiments. Full article

(This article belongs to the Special Issue Neutron Lifetime)

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24 pages, 388 KiB

Open AccessArticle

First Principles Description of Plasma Expansion Using the Expanding Box Model

by Sebastián Echeverría-Veas, Pablo S. Moya, Marian Lazar and Stefaan Poedts

Universe 2023, 9(10), 448; https://doi.org/10.3390/universe9100448 - 14 Oct 2023

Viewed by 1119

Abstract

Multi-scale modeling of expanding plasmas is crucial for understanding the dynamics and evolution of various astrophysical plasma systems such as the solar and stellar winds. In this context, the Expanding Box Model (EBM) provides a valuable framework to mimic plasma expansion in a [...] Read more.

Multi-scale modeling of expanding plasmas is crucial for understanding the dynamics and evolution of various astrophysical plasma systems such as the solar and stellar winds. In this context, the Expanding Box Model (EBM) provides a valuable framework to mimic plasma expansion in a non-inertial reference frame, co-moving with the expansion but in a box with a fixed volume, which is especially useful for numerical simulations. Here, fundamentally based on the Vlasov equation for magnetized plasmas and the EBM formalism for coordinates transformations, for the first time, we develop a first principles description of radially expanding plasmas in the EB frame. From this approach, we aim to fill the gap between simulations and theory at microscopic scales to model plasma expansion at the kinetic level. Our results show that expansion introduces non-trivial changes in the Vlasov equation (in the EB frame), especially affecting its conservative form through non-inertial forces purely related to the expansion. In order to test the consistency of the equations, we also provide integral moments of the modified Vlasov equation, obtaining the related expanding moments (i.e., continuity, momentum, and energy equations). Comparing our results with the literature, we obtain the same fluids equations (ideal-MHD), but starting from a first principles approach. We also obtained the tensorial form of the energy/pressure equation in the EB frame. These results show the consistency between the kinetic and MHD descriptions. Thus, the expanding Vlasov kinetic theory provides a novel framework to explore plasma physics at both micro and macroscopic scales in complex astrophysical scenarios. Full article

(This article belongs to the Special Issue The Multi-Scale Dynamics of Solar Wind)

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13 pages, 380 KiB

Open AccessArticle

Superluminal Local Operations in Quantum Field Theory: A Ping-Pong Ball Test

by Albert Much and Rainer Verch

Universe 2023, 9(10), 447; https://doi.org/10.3390/universe9100447 - 11 Oct 2023

Cited by 2 | Viewed by 1128

Abstract

It is known that, in quantum field theory, localized operations, e.g., given by unitary operators in local observable algebras, may lead to non-causal, or superluminal, state changes within their localization region. In this article, it is shown that, both in quantum field theory [...] Read more.

It is known that, in quantum field theory, localized operations, e.g., given by unitary operators in local observable algebras, may lead to non-causal, or superluminal, state changes within their localization region. In this article, it is shown that, both in quantum field theory as well as in classical relativistic field theory, there are localized operations which correspond to “instantaneous” spatial rotations (leaving the localization region invariant) leading to superluminal effects within the localization region. This shows that “impossible measurement scenarios” which have been investigated in the literature, and which rely on the presence of localized operations that feature superluminal effects within their localization region, do not only occur in quantum field theory, but also in classical field theory. Full article

(This article belongs to the Special Issue The Physics of Time Travel)

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15 pages, 1618 KiB

Open AccessEditor’s ChoiceReview

Main Results from the ISSI International Team “Characterization of 67P Cometary Activity”

by Andrea Longobardo, Minjae Kim, Boris Pestoni, Mauro Ciarniello, Giovanna Rinaldi, Stavro Ivanovski, Fabrizio Dirri, Marco Fulle, Vincenzo Della Corte, Alessandra Rotundi and Martin Rubin

Universe 2023, 9(10), 446; https://doi.org/10.3390/universe9100446 - 11 Oct 2023

Viewed by 1163

Abstract

The ESA/Rosetta mission accompanied the Jupiter Family Comet 67P/Churyumov-Gerasimenko and provided a huge amount of data which are providing important results about cometary activity mechanisms. We summarize the results obtained within the ISSI International Team Characterization of 67P cometary activity, which studied [...] Read more.

The ESA/Rosetta mission accompanied the Jupiter Family Comet 67P/Churyumov-Gerasimenko and provided a huge amount of data which are providing important results about cometary activity mechanisms. We summarize the results obtained within the ISSI International Team Characterization of 67P cometary activity, which studied dust and gas ejection in different stages of the comet’s orbit, by means of a data fusion between instruments onboard the Rosetta orbiter, i.e., the OSIRIS camera, the VIRTIS imaging spectrometer, the GIADA dust detector, the MIDAS atomic force microscope, the COSIMA dust mass spectrometer, and the ROSINA gas mass spectrometer, supported by numerical models and experimental work. The team reconstructed the motion of the dust particles ejected from the comet surface, finding a correlation between dust ejection and solar illumination as well as larger occurrence of fluffy (pristine) particles in less processed and more pebble-rich terrains. Dust activity is larger in ice-rich terrains, indicating that water sublimation is the dominant activity process during the perihelion phase. The comparison of dust fluxes of different particle size suggests a link between dust morphology and ejection speed, generation of micrometric dust from fragmentation of millimetric dust, and homogeneity of physical properties of compact dust particles across the 67P surface. The comparison of fluxes of refractory and ice particles suggests the occurrence of a small amount of ice in fluffy particles, which is released when they are fragmented. A new model of cometary activity has been finally developed, according to which the comet nucleus includes Water-Ice-Enriched Blocks (WEBs), that, when exposed by CO₂ activity, are the main sources of water sublimation and dust ejection. Full article

(This article belongs to the Special Issue Comets: Tracers of Solar System Formation and Evolution—Celebrating the 20th Anniversary of Rosetta Mission Launch)

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7 pages, 250 KiB

Open AccessArticle

Nothing into Something and Vice Versa: A Cosmological Scenario

by Leonid Marochnik

Universe 2023, 9(10), 445; https://doi.org/10.3390/universe9100445 - 09 Oct 2023

Viewed by 1067

Abstract

In the almost empty universe (with almost no matter in it), stochastic gravitational waves (SGW) of finite amplitude produce a de Sitter regime as a solution, which is invariant with respect to the Wick rotation. Asymptotically, super horizon SGWs do not “feel” difference [...] Read more.

In the almost empty universe (with almost no matter in it), stochastic gravitational waves (SGW) of finite amplitude produce a de Sitter regime as a solution, which is invariant with respect to the Wick rotation. Asymptotically, super horizon SGWs do not “feel” difference between Lorentzian and Euclidean spacetime and belong simultaneously to both of them. The universe is finishing its evolution in Euclidean spacetime, i.e., it disappears into nothing. Quantum fluctuations of the gravitational field (gravitons) produce a de Sitter regime again in Euclidean spacetime where the current universe finished its existence, and due to the invariance of the de Sitter regime with respect to Wick rotation, the next universe starts its life with de Sitter inflation in Lorentzian spacetime. Such a scenario assumes that a permanent process of birth, death and rebirth of an infinite sequence of universes takes place on an infinite time axis. Full article

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

15 pages, 534 KiB

Open AccessArticle

Effect of Spin-Dependent Short-Range Correlations on Nuclear Matrix Elements for Neutrinoless Double Beta Decay of ⁴⁸Ca

by Shahariar Sarkar and Yoritaka Iwata

Universe 2023, 9(10), 444; https://doi.org/10.3390/universe9100444 - 03 Oct 2023

Cited by 1 | Viewed by 1150

Abstract

Neutrinoless double beta decay is a pivotal weak nuclear process that holds the potential to unveil the Majorana nature of neutrinos and predict their absolute masses. In this study, we delve into examining the impact of spin-dependent short-range correlations (SRCs) on the nuclear [...] Read more.

Neutrinoless double beta decay is a pivotal weak nuclear process that holds the potential to unveil the Majorana nature of neutrinos and predict their absolute masses. In this study, we delve into examining the impact of spin-dependent short-range correlations (SRCs) on the nuclear matrix elements (NMEs) for the light neutrino-exchange mechanism in neutrinoless double beta (

0 ν β β

) decay of

^{48}

Ca, employing an extensive interacting nuclear shell model. All computations are performed employing the effective shell model Hamiltonian GXPF1A, encompassing the entire

f p

model space through the closure approximation. Our investigation examines the NMEs’ dependencies on factors such as the number of intermediate states, coupled spin-parity attributes of neutrons and protons, neutrino momentum, inter-nucleon separation, and closure energy. This scrutiny is performed with respect to both the conventional Jastrow-type approach of SRCs, employing various parameterizations, and the spin-dependent SRC paradigm. Our findings illuminate a discernible distinction in NMEs induced by spin-dependent SRCs, differing by approximately 10–20% from those computed through the conventional Jastrow-type SRCs, incorporating distinct parameterizations. Full article

(This article belongs to the Special Issue Recent Advances in Double Beta Decay Investigations: In Honor of Prof. Sabin Stoica at His 70th Anniversary)

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13 pages, 316 KiB

Open AccessArticle

Analogue Gravitational Lensing in Bose-Einstein Condensates

by Decheng Ma, Chenglong Jia, Enrique Solano and Lucas Chibebe Céleri

Universe 2023, 9(10), 443; https://doi.org/10.3390/universe9100443 - 01 Oct 2023

Viewed by 1161

Abstract

We consider the propagation of phonons in the presence of a particle sink with radial flow in a Bose–Einstein condensate. Because the particle sink can be used to simulate a static acoustic black hole, the phonon would experience a considerable spacetime curvature at [...] Read more.

We consider the propagation of phonons in the presence of a particle sink with radial flow in a Bose–Einstein condensate. Because the particle sink can be used to simulate a static acoustic black hole, the phonon would experience a considerable spacetime curvature at appreciable distance from the sink. The trajectory of the phonons is bended after passing by the particle sink, which can be used as a simulation of the gravitational lensing effect in a Bose–Einstein condensate. Possible experimental implementations are discussed. Full article

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

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46 pages, 25189 KiB

Open AccessReview

Fine Structure of Solar Metric Radio Bursts: ARTEMIS-IV/JLS and NRH Observations

by Costas Alissandrakis, Alexander Hillaris, Costas Bouratzis and Spyros Armatas

Universe 2023, 9(10), 442; https://doi.org/10.3390/universe9100442 - 30 Sep 2023

Cited by 1 | Viewed by 1375

Abstract

Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of [...] Read more.

Radio bursts provide important diagnostics of energetic phenomena of the Sun. In particular, bursts in decimetric and metric wavelengths probe the physical conditions and the energy release processes in the low corona as well as their association with heliospheric phenomena. The advent of spectral radio data with high time and high frequency resolution has provided a wealth of information on phenomena of short duration and narrow bandwidth. Of particular value are spectral data combined with imaging observations at specific frequencies. In this work we briefly review the results of a series of observations comprised from high-sensitivity, low-noise dynamic spectra obtained with the acousto-optic analyzer (SAO) of the ARTEMIS-IV/JLS solar radiospectrograph, in conjunction with high time-resolution images from the Nançay Radioheliograph (NRH). Our studies include fine structures embedded in type-IV burst continua (mostly narrow-band “spikes” and intermediate drift “fiber” bursts) and spike-like structures detected near the front of type-II bursts. The implications of the observational results to theoretical models are discussed. Full article

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

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12 pages, 14170 KiB

Open AccessArticle

Variations in Pulsating Aurora Emission in 337 nm and 391 nm Nitrogen Spectral Lines during Geomagnetic Substorms

by Pavel Klimov, Vera Nikolaeva, Alexander Belov, Boris Kozelov, Alexei Murashov, Alexei Roldugin and Sergei Sharakin

Universe 2023, 9(10), 441; https://doi.org/10.3390/universe9100441 - 30 Sep 2023

Viewed by 1058

Abstract

Spectroscopic measurements of aurora emissions provide valuable insights into the altitude of electron atmospheric penetration and their maximum energy. To achieve this, the photometers used in the PAIPS (Pulsating Aurora Imaging Photometers System) project are equipped with spectrometers. These spectrometers enable the measurement [...] Read more.

Spectroscopic measurements of aurora emissions provide valuable insights into the altitude of electron atmospheric penetration and their maximum energy. To achieve this, the photometers used in the PAIPS (Pulsating Aurora Imaging Photometers System) project are equipped with spectrometers. These spectrometers enable the measurement of auroral emissions in narrow spectral lines with a temporal resolution of milliseconds. In this study, we present two cases of PsA (Pulsating Aurora) measurements in the 337 nm and 391 nm spectral lines. We demonstrate that during quiet geomagnetic conditions the ratio of night sky emissions in these bands is close to one and significantly increases during substorms. We propose and implement a special procedure for estimating this ratio. Our findings reveal that the intensity of emissions in both spectral lines correlates with the AL index of geomagnetic activity. However, the ratio between the emissions fluctuates around constant values over time and does not undergo significant changes throughout the entire PsA event, which can last for more than an hour. Full article

(This article belongs to the Special Issue Auroral Physics)

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41 pages, 1380 KiB

Open AccessArticle

CKM Matrix Parameters from the Exceptional Jordan Algebra

by Aditya Ankur Patel and Tejinder P. Singh

Universe 2023, 9(10), 440; https://doi.org/10.3390/universe9100440 - 30 Sep 2023

Cited by 2 | Viewed by 1681

Abstract

We report a theoretical derivation of the Cabibbo–Kobayashi–Maskawa (CKM) matrix parameters and the accompanying mixing angles. These results are arrived at from the exceptional Jordan algebra applied to quark states, and from expressing flavor eigenstates (i.e., left chiral states) as a superposition of [...] Read more.

We report a theoretical derivation of the Cabibbo–Kobayashi–Maskawa (CKM) matrix parameters and the accompanying mixing angles. These results are arrived at from the exceptional Jordan algebra applied to quark states, and from expressing flavor eigenstates (i.e., left chiral states) as a superposition of mass eigenstates (i.e., the right chiral states) weighted by the square root of mass. Flavor mixing for quarks is mediated by the square root mass eigenstates, and the mass ratios used are derived from earlier work from a left–right symmetric extension of the standard model. This permits a construction of the CKM matrix from first principles. There exist only four normed division algebras, and they can be listed as follows: the real numbers

R

, the complex numbers

C

, the quaternions

H

and the octonions

O

. The first three algebras are fairly well known; however, octonions as algebra are less studied. Recent research has pointed towards the importance of octonions in the study of high-energy physics. Clifford algebras and the standard model are being studied closely. The main advantage of this approach is that the spinor representations of the fundamental fermions can be constructed easily here as the left ideals of the algebra. Also, the action of various spin groups on these representations can also be studied easily. In this work, we build on some recent advances in the field and try to determine the CKM angles from an algebraic framework. We obtain the mixing angle values as

θ_{12} = {11.093}^{\circ}, θ_{13} = {0.172}^{\circ}, θ_{23} = {4.054}^{\circ}

. In comparison, the corresponding experimentally measured values for these angles are

{13.04}^{\circ} \pm {0.05}^{\circ}, {0.201}^{\circ} \pm {0.011}^{\circ}, {2.38}^{\circ} \pm {0.06}^{\circ}

. The agreement of theory with experiment is likely to improve when the running of quark masses is taken into account. Full article

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

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37 pages, 2670 KiB

Open AccessReview

Single-Top Quark Physics at the LHC: From Precision Measurements to Rare Processes and Top Quark Properties

by Jérémy Andrea and Nicolas Chanon

Universe 2023, 9(10), 439; https://doi.org/10.3390/universe9100439 - 30 Sep 2023

Viewed by 1207

Abstract

Since the initial measurements of single-top quark production at the Tevatron in 2009, tremendous progress has been made at the LHC. While LHC Run 1 marked the beginning of a precision era for the single-top quark measurements in some of the main production [...] Read more.

Since the initial measurements of single-top quark production at the Tevatron in 2009, tremendous progress has been made at the LHC. While LHC Run 1 marked the beginning of a precision era for the single-top quark measurements in some of the main production mechanisms, LHC Run 2 witnessed the emergence and exploration of new processes associating top quark production with a neutral boson. In this paper, we review the measurements of the three main production mechanisms (t-channel, s-channel, and

t W

production), and of the associated production with a photon, a Z boson, or a Higgs boson. Differential cross-sections are measured for several of these processes and compared with theoretical predictions. The top quark properties that can be measured in single-top quark processes are scrutinized, such as

W t b

couplings and top quark couplings with neutral bosons, and the polarizations of both the W boson and top quark. The effective field theory framework is emerging as a standard for interpreting property measurements. Perspectives for LHC Run 3 and the HL-LHC are discussed in the conclusions. Full article

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

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9 pages, 1295 KiB

Open AccessArticle

Probing the Elastic Scattering Differential Cross Section for Al + p at Backward Angles in a Low Energy Regime

by Javier Mas Ruiz, Karla Gutierrez Zayas-Bazán, Patricia G. Zayas-Bazán, Arcadio Huerta, Jorge Sastré-Hernández, Daniel José Marín-Lámbarri, Luis Acosta, Eduardo Andrade, Corina Solís and Efrain R. Chávez Lomelí

Universe 2023, 9(10), 438; https://doi.org/10.3390/universe9100438 - 30 Sep 2023

Viewed by 1010

Abstract

We report on the absolute differential cross section for proton elastic scattering on aluminum in the energy range of 0.8 MeV to 2.1 MeV. In the literature we have found previously published data that follow similar trends but are not consistent with one [...] Read more.

We report on the absolute differential cross section for proton elastic scattering on aluminum in the energy range of 0.8 MeV to 2.1 MeV. In the literature we have found previously published data that follow similar trends but are not consistent with one another. The present measurements also fall within that range, moreover, covering angular regions where there were no reported data, improving databases such as IBANDL. Different methods for the optical model calculations are shown where angular distributions at backward angles are in good agreement, allowing one to fix the optical potential parameters. The calculation results, as well as their data fit, differ significantly as one would expect for the energy range covered in this work, where the nuclear part of the interaction contribution is almost zero. Our data, as well as previous reports, suggest an increase with higher energies for the value of the elastic cross section at backward angles. Further work is required from both experimental and theoretical fronts. Full article

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

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16 pages, 775 KiB

Open AccessArticle

An Effective Sign Switching Dark Energy: Lotka–Volterra Model of Two Interacting Fluids

by Yen Chin Ong

Universe 2023, 9(10), 437; https://doi.org/10.3390/universe9100437 - 30 Sep 2023

Cited by 9 | Viewed by 1277

Abstract

One of the recent attempts to address the Hubble and

S_{8}

tensions is to consider that the Universe started out not as a de Sitter-like spacetime, but rather anti-de Sitter-like. That is, the Universe underwent an “AdS-to-dS” transition at some point. We [...] Read more.

One of the recent attempts to address the Hubble and

S_{8}

tensions is to consider that the Universe started out not as a de Sitter-like spacetime, but rather anti-de Sitter-like. That is, the Universe underwent an “AdS-to-dS” transition at some point. We study the possibility that there are two dark energy fluids, one of which gave rise to the anti-de Sitter-like early Universe. The interaction is modeled by the Lotka–Volterra equations commonly used in population biology. We consider “competition” models that are further classified as “unfair competition” and “fair competition”. The former involves a quintessence in competition with a phantom, and the second involves two phantom fluids. Surprisingly, even in the latter scenario it is possible for the overall dark energy to cross the phantom divide. The latter model also allows a constant w “AdS-to-dS” transition, thus evading the theorem that such a dark energy must possess a singular equation of state. We also consider a “conversion” model in which a phantom fluid still manages to achieve “AdS-to-dS” transition even if it is being converted into a negative energy density quintessence. In these models, the energy density of the late time effective dark energy is related to the coefficient of the quadratic self-interaction term of the fluids, which is analogous to the resource capacity in population biology. Full article

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

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20 pages, 5963 KiB

Open AccessArticle

Random Forest Classification and Ionospheric Response to Solar Flares: Analysis and Validation

by Filip Arnaut, Aleksandra Kolarski and Vladimir A. Srećković

Universe 2023, 9(10), 436; https://doi.org/10.3390/universe9100436 - 30 Sep 2023

Cited by 5 | Viewed by 1181

Abstract

The process of manually checking, validating, and excluding data in an ionospheric very-low-frequency (VLF) analysis during extreme events is a labor-intensive and time-consuming task. However, this task can be automated through the utilization of machine learning (ML) classification techniques. This research paper employed [...] Read more.

The process of manually checking, validating, and excluding data in an ionospheric very-low-frequency (VLF) analysis during extreme events is a labor-intensive and time-consuming task. However, this task can be automated through the utilization of machine learning (ML) classification techniques. This research paper employed the Random Forest (RF) classification algorithm to automatically classify the impact of solar flares on ionospheric VLF data and erroneous data points, such as instrumentation errors and noisy data. The data used for analysis were collected during September and October 2011, encompassing solar flare classes ranging from C2.5 to X2.1. The F1-score values obtained from the test dataset displayed values of 0.848; meanwhile, a more detailed analysis revealed that, due to the imbalanced distribution of the target class, the per-class F1-score indicated higher values for the normal data point class (0.69–0.97) compared to those of the anomalous data point class (0.31 to 0.71). Instances of successful and inadequate categorization were analyzed and presented visually. This research investigated the potential application of ML techniques in the automated identification and classification of erroneous VLF amplitude data points; however, the findings of this research hold promise for the detection of short-term ionospheric responses to, e.g., gamma ray bursts (GRBs), or in the analysis of pre-earthquake ionospheric anomalies. Full article

(This article belongs to the Special Issue New Insights into Astronomy and Earth Observations: From Observations to the Theory)

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18 pages, 7423 KiB

Open AccessArticle

Feature-Based Classification Neural Network for Kepler Light Curves from Quarter 1

by Jing Yan, Huanli Wu, Bo Qiu, A-Li Luo and Fuji Ren

Universe 2023, 9(10), 435; https://doi.org/10.3390/universe9100435 - 28 Sep 2023

Viewed by 1286

Abstract

Determining the types of light curves has been a challenge due to the massive amount of light curves generated by large sky survey programs. In the literature, the light curves classification methods are overly dependent on the imaging quality of the light curves, [...] Read more.

Determining the types of light curves has been a challenge due to the massive amount of light curves generated by large sky survey programs. In the literature, the light curves classification methods are overly dependent on the imaging quality of the light curves, so the classification results are often poor. In this paper, a new method is proposed to classify the Kepler light curves from Quarter 1, and consists of two parts: feature extraction and classification neural network construction. In the first part, features are extracted from the light curves using three different methods, and then the features are fused (transform domain features, light curve flux statistics features, and Kepler photometry features). In the second part, a classification neural network RLNet, based on Residual Network (ResNet) and Long Short Term Memory (LSTM), is proposed. The experiment involved the classification of approximately 150,000 Kepler light curves into 11 categories. The results show that this new method outperforms seven other methods in all metrics, with an accuracy of 0.987, a minimum recall of 0.968, and a minimum precision of 0.970 under all categories. Full article

(This article belongs to the Section Stellar Astronomy)

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12 pages, 496 KiB

Open AccessArticle

Thermal Effects in Ising Cosmology

by Nikos Irges, Antonis Kalogirou and Fotis Koutroulis

Universe 2023, 9(10), 434; https://doi.org/10.3390/universe9100434 - 28 Sep 2023

Cited by 1 | Viewed by 967

Abstract

We consider a real scalar field in de Sitter background and compute its thermal propagators. We propose that in a dS/CFT context, nontrivial thermal effects as seen by an ‘out’ observer can be encoded in the anomalous dimensions of the

d = 3

[...] Read more.

We consider a real scalar field in de Sitter background and compute its thermal propagators. We propose that in a dS/CFT context, nontrivial thermal effects as seen by an ‘out’ observer can be encoded in the anomalous dimensions of the

d = 3

Ising model. One of these anomalous dimensions, the critical exponent

η

, completely fixes a number of cosmological observables, which we compute. Full article

(This article belongs to the Section Cosmology)

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17 pages, 525 KiB

Open AccessArticle

Space–Time Structure of Particle Emission and Femtoscopy Scales in Ultrarelativistic Heavy-Ion Collisions

by Yuri Sinyukov, Volodymyr Shapoval and Musfer Adzhymambetov

Universe 2023, 9(10), 433; https://doi.org/10.3390/universe9100433 - 28 Sep 2023

Cited by 1 | Viewed by 1073

Abstract

The analysis of the spatiotemporal picture of particle radiation in relativistic heavy-ion collisions in terms of correlation femtoscopy scales, emission, and source functions allows one to probe the character of the evolution of the system created in the collision. Realistic models, such as [...] Read more.

The analysis of the spatiotemporal picture of particle radiation in relativistic heavy-ion collisions in terms of correlation femtoscopy scales, emission, and source functions allows one to probe the character of the evolution of the system created in the collision. Realistic models, such as the integrated hydrokinetic model (iHKM), used in the present work, are able to simulate the entire evolution process of strongly interacting matter produced in high-energy nuclear collisions. The mentioned model describes all the stages of the system’s evolution, including thermalisation and hydrodynamisation, which can help researchers figure out the specific details of the process and better understand the formation mechanisms of certain observables. In the current paper, we investigated the behaviour of the pion and kaon interferometry radii and their connection with emission functions in ultrarelativistic heavy-ion collisions at the Large Hadron Collider within iHKM. We focused on the study of the emission time scales at different energies for both particle species (pions and kaons) aiming to gain deeper insight into relation of these scales and the peculiarities of the mentioned system’s collective expansion and decay with the experimentally observed femtoscopy radii. One of our main interests was the problem of the total system’s lifetime estimation based on the femtoscopy analysis. Full article

(This article belongs to the Special Issue Collectivity in High-Energy Proton-Proton and Heavy-Ion Collisions)

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25 pages, 954 KiB

Open AccessArticle

Release Episodes of Electrons and Protons in Solar Energetic Particle Events

by Vasilis Kolympiris, Athanasios Papaioannou, Athanasios Kouloumvakos, Ioannis A. Daglis and Anastasios Anastasiadis

Universe 2023, 9(10), 432; https://doi.org/10.3390/universe9100432 - 27 Sep 2023

Viewed by 1382

Abstract

We analyzed a sample of 21 solar energetic particle (SEP) events with clear signatures in both near-relativistic electrons and high-energy protons spanning over ∼2.5 solar cycles from 1997 to 2016. We employed velocity dispersion analysis (VDA) for protons and fractional VDA (FVDA) for [...] Read more.

We analyzed a sample of 21 solar energetic particle (SEP) events with clear signatures in both near-relativistic electrons and high-energy protons spanning over ∼2.5 solar cycles from 1997 to 2016. We employed velocity dispersion analysis (VDA) for protons and fractional VDA (FVDA) for electrons, as well as time shifting analysis (TSA) in order to identify the solar release times (SRTs) of the electrons. We found that, for the majority of the events (62%), a simultaneous release was observed, while, for 14% of the events, electrons were released later than protons (i.e., delayed electrons); for 24% of the events, the opposite result was found (i.e., delayed protons). We found that the path length (L) traveled by the protons and electrons was not related to the aforementioned categorization. Moreover, we show that, in the case of simultaneous SEP events, protons and electrons are being released in close connection to type III and type II bursts, while the opposite is the case for delayed events. In addition, we demonstrate that, for the simultaneous events, both the proton and the electron release are established in heights < 5

R_{S}

and that, especially for the well-connected simultaneous events, there is a co-occurrence of the type II burst with the release time of the particles. Full article

(This article belongs to the Special Issue Solar Energetic Particles)

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17 pages, 1612 KiB

Open AccessArticle

The Formulation of Scaling Expansion in an Euler-Poisson Dark-Fluid Model

by Balázs Endre Szigeti, Imre Ferenc Barna and Gergely Gábor Barnaföldi

Universe 2023, 9(10), 431; https://doi.org/10.3390/universe9100431 - 27 Sep 2023

Viewed by 928

Abstract

We present a dark fluid model described as a non-viscous, non-relativistic, rotating, and self-gravitating fluid. We assume that the system has spherical symmetry and that the matter can be described by the polytropic equation of state. The induced coupled nonlinear partial differential system [...] Read more.

We present a dark fluid model described as a non-viscous, non-relativistic, rotating, and self-gravitating fluid. We assume that the system has spherical symmetry and that the matter can be described by the polytropic equation of state. The induced coupled nonlinear partial differential system of equations was solved using a self-similar time-dependent ansatz introduced by L. Sedov and G.I. Taylor. These kinds of solutions were successfully used to describe blast waves induced by an explosion following the Guderley–Landau–Stanyukovich problem. We show that the result of our quasi-analytic solutions are fully consistent with the Newtonian cosmological framework. We analyzed relevant quantities from the model, namely, the evolution of the Hubble parameter and the density parameter ratio, finding that our solutions can be applied to describe normal-to-dark energy on the cosmological scale. Full article

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

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24 pages, 831 KiB

Open AccessArticle

Jerk Parameter and Modified Theory

by Değer Sofuoğlu and Aroonkumar Beesham

Universe 2023, 9(10), 430; https://doi.org/10.3390/universe9100430 - 27 Sep 2023

Viewed by 963

Abstract

The accelerated expansion of the universe during recent times is well known in cosmology, whereas during early times, there was decelerated expansion. The

Λ

CDM model is consistent with most observations, but there are some issues with it. In addition, the transition from [...] Read more.

The accelerated expansion of the universe during recent times is well known in cosmology, whereas during early times, there was decelerated expansion. The

Λ

CDM model is consistent with most observations, but there are some issues with it. In addition, the transition from early deceleration to late-time acceleration cannot be explained by general relativity. Hence, it is worthwhile to examine modified gravity theories to explain this transition and to get a better understanding of dark energy. In this work, dark energy in modified

f (R, T)

gravity is investigated, where R is the Ricci scalar and T is the trace of the energy momentum tensor. Normally, the simplest form of

f (R, T)

is used, viz.,

f (R) = R + λ T

. In this work, the more complicated form

f (R, T) = R + R T

is investigated in Friedmann–Lemaître–Robertson–Walker spacetime. This form has not been well studied. Since the jerk parameter in general relativity is constant and

j = 1

, in order to have as small a departure from general relativity as possible, the jerk parameter

j = 1

is also assumed here. This enables the complete solution for the scale factor to be found. One of these forms is used for a complete analysis and is compared with the usually studied form

f (R, T) = R + R T

. The solution can also be broken down into a power-law form at early times (deceleration) and an exponential form at late times (acceleration), which makes the analysis simpler. Surprisingly, each of these forms is also a solution to the differential equation

j = 1

(though they are not solutions to the general solution). The energy conditions are also studied, and plots are provided. It is shown that viable models can be obtained without the need for the introduction of a cosmological constant, which reduces to the

Λ

CDM at late times. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Electronic Conference on Universe (ECU 2023))

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15 pages, 723 KiB

Open AccessArticle

Axionic Dark Matter in a Bi-Metric Universe

by Carlos Maldonado and Fernando Méndez

Universe 2023, 9(10), 429; https://doi.org/10.3390/universe9100429 - 27 Sep 2023

Viewed by 1377

Abstract

We study the evolution and production of axion dark matter in a universe model with two scale factors corresponding to different patches of the universe. The interaction between patches is described through a deformed Poisson bracket structure. The first part of the present [...] Read more.

We study the evolution and production of axion dark matter in a universe model with two scale factors corresponding to different patches of the universe. The interaction between patches is described through a deformed Poisson bracket structure. The first part of the present paper is devoted to a review of the results reported in previous works concerning the study of dark matter as WIMPs and FIMPs. The new results concerning axionic dark matter in this bi-metric scenario show that different values of the deformation parameter

κ

allow values of masses and misalignment angles forbidden in standard cosmology. The present model can also be considered a different type of nonstandard cosmology consistent with previously reported results. Full article

(This article belongs to the Section Cosmology)

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24 pages, 9799 KiB

Open AccessArticle

A Wheeler–DeWitt Non-Commutative Quantum Approach to the Branch-Cut Gravity

by Benno Bodmann, Dimiter Hadjimichef, Peter Otto Hess, José de Freitas Pacheco, Fridolin Weber, Moisés Razeira, Gervásio Annes Degrazia, Marcelo Marzola and César A. Zen Vasconcellos

Universe 2023, 9(10), 428; https://doi.org/10.3390/universe9100428 - 26 Sep 2023

Cited by 4 | Viewed by 1229

Abstract

In this contribution, motivated by the quest to understand cosmic acceleration, based on the theory of Hořava–Lifshitz and on the branch-cut gravitation, we investigate the effects of non-commutativity of a mini-superspace of variables obeying the Poisson algebra on the structure of the branch-cut [...] Read more.

In this contribution, motivated by the quest to understand cosmic acceleration, based on the theory of Hořava–Lifshitz and on the branch-cut gravitation, we investigate the effects of non-commutativity of a mini-superspace of variables obeying the Poisson algebra on the structure of the branch-cut scale factor and on the acceleration of the Universe. We follow the guiding lines of a previous approach, which we complement to allow a symmetrical treatment of the Poisson algebraic variables and eliminate ambiguities in the ordering of quantum operators. On this line of investigation, we propose a phase-space transformation that generates a super-Hamiltonian, expressed in terms of new variables, which describes the behavior of a Wheeler–DeWitt wave function of the Universe within a non-commutative algebraic quantum gravity formulation. The formal structure of the super-Hamiltonian allows us to identify one of the new variables with a modified branch-cut quantum scale factor, which incorporates, as a result of the imposed variable transformations, in an underlying way, elements of the non-commutative algebra. Due to its structural character, this algebraic structure allows the identification of the other variable as the dual quantum counterpart of the modified branch-cut scale factor, with both quantities scanning reciprocal spaces. Using the iterative Range–Kutta–Fehlberg numerical analysis for solving differential equations, without resorting to computational approximations, we obtained numerical solutions, with the boundary conditions of the wave function of the Universe based on the Bekenstein criterion, which provides an upper limit for entropy. Our results indicate the acceleration of the early Universe in the context of the non-commutative branch-cut gravity formulation. These results have implications when confronted with information theory; so to accommodate gravitational effects close to the Planck scale, a formulation à la Heisenberg’s Generalized Uncertainty Principle in Quantum Mechanics involving the energy and entropy of the primordial Universe is proposed. Full article

(This article belongs to the Section Gravitation)

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7 pages, 235 KiB

Open AccessArticle

Singularities of Scattering Matrices

by Albert Schwarz

Universe 2023, 9(10), 427; https://doi.org/10.3390/universe9100427 - 25 Sep 2023

Viewed by 873

Abstract

Our main result is the analysis of singularities of the integrands of integrals representing the matrix elements of the scattering matrix and the inclusive scattering matrix in perturbation theory. These results are proven for any quantum field theory in any dimension. Full article

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

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