Universe

10 pages, 457 KiB

Open AccessArticle

Black String Solutions in Rainbow Gravity

by Roberta Dárlla, Francisco A. Brito and Job Furtado

Universe 2023, 9(6), 297; https://doi.org/10.3390/universe9060297 - 20 Jun 2023

Cited by 4 | Viewed by 776

In this paper, we studied black string solutions under the consideration of rainbow gravity. We analytically obtained the solution for four-dimensional black strings in terms of the functions

f (E / E_{p})

and

g (E / E_{p})

[...] Read more.

In this paper, we studied black string solutions under the consideration of rainbow gravity. We analytically obtained the solution for four-dimensional black strings in terms of the functions

f (E / E_{p})

and

g (E / E_{p})

that sets the energy scale where the rainbow gravity becomes relevant. We also obtained the Hawking temperature for the black string, from which we can see that the rainbow functions play the role of increasing or decreasing the Hawking temperature for a given horizon radius depending on the choice of such rainbow functions. We computed the entropy, specific heat and free energy for the black string. The entropy and specific heat exhibit a rainbow dependence, whereas the free energy is not modified by the rainbow functions. Finally, we studied the effects of rainbow gravity in the orbits of massive and massless particles around a black string. We could verify that neither massive nor massless particles exhibit stable orbits around a black string in the scenario of rainbow gravity for any configuration of rainbow functions. Full article

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

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13 pages, 4045 KiB

Open AccessArticle

Pyroxene and Hydroxyl Signatures in Vesta Newly Calibrated Data from Dawn Mission

by Giuseppe Massa, Andrea Longobardo, Ernesto Palomba, Marianna Angrisani, Chiara Gisellu, Fabrizio Dirri, Maria Cristina De Sanctis, Andrea Raponi, Filippo Giacomo Carrozzo and Mauro Ciarniello

Universe 2023, 9(6), 296; https://doi.org/10.3390/universe9060296 - 19 Jun 2023

Cited by 2 | Viewed by 988

Abstract

Thanks to the VIR spectrometer onboard NASA’s Dawn spacecraft, which orbited Vesta in 2011–2012, thousands of hyperspectral images of its surface have been collected. The mission confirmed the HED (Howardite–Eucrite–Diogenite) meteorite composition of Vesta. Moreover, the VIR spectrometer detected the 2.8 µm absorption [...] Read more.

Thanks to the VIR spectrometer onboard NASA’s Dawn spacecraft, which orbited Vesta in 2011–2012, thousands of hyperspectral images of its surface have been collected. The mission confirmed the HED (Howardite–Eucrite–Diogenite) meteorite composition of Vesta. Moreover, the VIR spectrometer detected the 2.8 µm absorption band, due to the presence of the OH molecule. In this work, we took advantage of the newly calibrated data of the VIR spectrometer by characterizing new spectral features thanks to the improved signal-to-noise (S/N) ratio for these spectra. The main goals of this work are as follows: (1) to characterize Vesta’s surface in the visible range and (2) to confirm, reinforce and characterize the OH distribution on Vesta by studying the 2.8 µm band and looking for OH combination bands around 2.2–2.4 µm. A possible relation between the 1.9 µm absorption band due to the presence of pyroxenes and the one at 0.5 µm was analyzed. Finally, the analysis of hydroxyl absorption bands evidenced an anti-correlation between the abundance of hydroxyl-bearing molecules and the surface reflectance. This confirms that the hydroxyl presence is linked to the dark units on Vesta. Full article

(This article belongs to the Special Issue Space Missions to Small Bodies: Results and Future Activities)

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16 pages, 3193 KiB

Open AccessArticle

SN 2017fzw: A Fast-Expanding Type Ia Supernova with Transitional Features

by Jiayu Huang, Yangyang Li, Xiangyun Zeng, Sheng Zheng, Sarah A. Bird, Jujia Zhang, Ali Esamdin, Abdusamatjan Iskandar, K. Azaleee Bostroem, Shuguang Zeng, Yanshan Xiao, Yao Huang, D. Andrew Howell, Curtis McCully, Wenxiong Li, Tianmeng Zhang, Lifan Wang and Lei Hu

Universe 2023, 9(6), 295; https://doi.org/10.3390/universe9060295 - 17 Jun 2023

Cited by 1 | Viewed by 1129

Abstract

In this study, we analyzed the optical observations of a subluminous Type Ia supernova (SN Ia) 2017fzw, which exhibited high photospheric velocity (HV) at B-band maximum light. The absolute B-band peak magnitude was determined to be [...] Read more.

In this study, we analyzed the optical observations of a subluminous Type Ia supernova (SN Ia) 2017fzw, which exhibited high photospheric velocity (HV) at B-band maximum light. The absolute B-band peak magnitude was determined to be

M_{m a x}^{B} = - 18.65 \pm 0.13

mag, similar to 91bg-like SNe Ia. An estimation of the rate of decline for the B-band light curve was determined to be

Δ m_{15} (B) = 1.60 \pm 0.06

mag. The spectra of SN 2017fzw were similar to those of 91bg-like SNe Ia, with prominent Ti ii and Si ii

λ 5972

features at early phases, gradually transitioning to spectra resembling normal (mainly HV subclass) SNe Ia at later phases, with a stronger Ca ii NIR feature. Notably, throughout all phases of observation, SN 2017fzw displayed spectral evolution characteristics that were comparable to those of HV SNe Ia, and at peak brightness, the Si ii

λ 6355

velocity was determined to be 13,800

\pm 415

km s

^{- 1}

and a more pronounced Ca ii NIR feature was also detected. Based on these findings, we classify SN 2017fzw as a transitional object with properties of both normal and 91bg-like SNe Ia, providing support for the hypothesis of a continuous distribution of supernovae between these two groups. Full article

(This article belongs to the Section Stellar Astronomy)

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10 pages, 832 KiB

Open AccessCommunication

Production of Primordial Black Holes in Improved E-Models of Inflation

by Daniel Frolovsky and Sergei V. Ketov

Universe 2023, 9(6), 294; https://doi.org/10.3390/universe9060294 - 16 Jun 2023

Cited by 3 | Viewed by 834

Abstract

E-type

α

-attractor models of single-field inflation were generalized further in order to accommodate production of primordial black holes (PBHs) via adding a near-inflection point to the inflaton scalar potential at smaller scales, in good agreement with measurements of cosmic microwave background (CMB) [...] Read more.

E-type

α

-attractor models of single-field inflation were generalized further in order to accommodate production of primordial black holes (PBHs) via adding a near-inflection point to the inflaton scalar potential at smaller scales, in good agreement with measurements of cosmic microwave background (CMB) radiation. A minimal number of new parameters were used but their fine-tuning was maximized in order to increase the possible masses of PBHs formed during an ultra-slow-roll phase, leading to a large enhancement in the power spectrum of scalar (curvature) perturbations by 6 or 7 orders of magnitude against the power spectrum of perturbations observed in CMB. It was found that extreme fine-tuning of the parameters in our models can lead to the formation of moon-sized PBHs, with masses of up to

10^{26}

g, still in agreement with CMB observations. Quantum corrections are known to lead to the perturbative upper bound on the amplitude of large scalar perturbations responsible for PBH production. The quantum (one-loop) corrections in our models were found to be suppressed by one order of magnitude for PBHs with masses of approximately

10^{19}

g, which may form the whole dark matter in the Universe. Full article

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

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15 pages, 4056 KiB

Open AccessReview

The Formation of a Rubble Pile Asteroid: Insights from the Asteroid Ryugu

by Tsutomu Ota, Christian Potiszil, Katsura Kobayashi, Ryoji Tanaka, Hiroshi Kitagawa, Tak Kunihiro, Chie Sakaguchi, Masahiro Yamanaka and Eizo Nakamura

Universe 2023, 9(6), 293; https://doi.org/10.3390/universe9060293 - 16 Jun 2023

Cited by 1 | Viewed by 1363

Abstract

The Hayabusa2 mission returned primitive samples from the C-type asteroid Ryugu to Earth. The C-type asteroids hold clues to the origin of Earth’s water and the building blocks of life. The rubble pile structure of C-type asteroids is a crucial physical feature relating [...] Read more.

The Hayabusa2 mission returned primitive samples from the C-type asteroid Ryugu to Earth. The C-type asteroids hold clues to the origin of Earth’s water and the building blocks of life. The rubble pile structure of C-type asteroids is a crucial physical feature relating to their origin and evolution. A rubble pile asteroid is hypothesized to be bound primarily by self-gravity with a significant void space among irregularly shaped materials after catastrophic impacts between larger asteroids. However, the geological observations from Hayabusa2 and the analyses of the returned sample from Ryugu revealed that the high microporosity was common to various >10 m- to mm-sized materials of Ryugu, which suggests that the asteroid Ryugu is not just a loosely bound agglomeration of massive rocky debris from shattered asteroids. For a better understanding of the origin and evolution of the rubble pile asteroid, the current most accepted hypothesis should be verified by observations and laboratory analyses and improved upon based on this information. Here, the previous models are examined using Hayabusa2’s geological observations of the asteroid and the analytical data from the samples returned from Ryugu’s surface and subsurface material. Incorporating the new findings, a hypothesis for the evolution of the rubble pile asteroid Ryugu from a cometary nucleus through sublimation and subsequent dynamic resurfacing is proposed. The proposed hypothesis is applicable to other rubble-pile asteroids and would provide perspectives for near-Earth objects in general. Full article

(This article belongs to the Special Issue Space Missions to Small Bodies: Results and Future Activities)

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Graphical abstract

10 pages, 290 KiB

Open AccessArticle

Electromagnetic Waves in Cosmological Spacetime

by Denitsa Staicova and Michail Stoilov

Universe 2023, 9(6), 292; https://doi.org/10.3390/universe9060292 - 16 Jun 2023

Cited by 1 | Viewed by 857

Abstract

We consider the propagation of electromagnetic waves in the Friedmann–Lemaître–Robertson–Walker metric. The exact solutions for plane and spherical wave are written down. The corresponding redshift, amplitude change, and dispersion are discussed. We also speculate about the connection of the electromagnetic wave equation to [...] Read more.

We consider the propagation of electromagnetic waves in the Friedmann–Lemaître–Robertson–Walker metric. The exact solutions for plane and spherical wave are written down. The corresponding redshift, amplitude change, and dispersion are discussed. We also speculate about the connection of the electromagnetic wave equation to the Proca equation and its significance for the early Universe. Full article

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

13 pages, 1507 KiB

Open AccessArticle

Structure of the Medium Formed in Heavy Ion Collisions

by J. R. Alvarado García, D. Rosales Herrera, A. Fernández Téllez, Bogar Díaz and J. E. Ramírez

Universe 2023, 9(6), 291; https://doi.org/10.3390/universe9060291 - 15 Jun 2023

Cited by 1 | Viewed by 1306

Abstract

We investigate the structure of the medium formed in heavy ion collisions using three different models: the Color String Percolation Model (CSPM), the Core–Shell-Color String Percolation Model (CSCSPM), and the Color Glass Condensate (CGC) framework. We analyze the radial distribution function of the [...] Read more.

We investigate the structure of the medium formed in heavy ion collisions using three different models: the Color String Percolation Model (CSPM), the Core–Shell-Color String Percolation Model (CSCSPM), and the Color Glass Condensate (CGC) framework. We analyze the radial distribution function of the transverse representation of color flux tubes in each model to determine the medium’s structure. Our results indicate that the CSPM behaves as an ideal gas, while the CSCSPM exhibits a structural phase transition from a gas-like to a liquid-like structure. Additionally, our analysis of the CGC framework suggests that it produces systems that behave like non-ideal gases for AuAu central collisions at RHIC energies and liquid-like structures for PbPb central collisions at LHC energies. Full article

(This article belongs to the Special Issue Relativistic Heavy Ion Collision)

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13 pages, 544 KiB

Open AccessReview

Double Beta Decay Experiments: Recent Achievements and Future Prospects

by Alexander Barabash

Universe 2023, 9(6), 290; https://doi.org/10.3390/universe9060290 - 15 Jun 2023

Cited by 4 | Viewed by 964

Abstract

The results of experiments on the search for and study of double beta decay processes obtained over the past 5 years (from 2018 to April 2023) are discussed. The results of the search for neutrinoless double beta decay are presented, in which a [...] Read more.

The results of experiments on the search for and study of double beta decay processes obtained over the past 5 years (from 2018 to April 2023) are discussed. The results of the search for neutrinoless double beta decay are presented, in which a sensitivity of

T_{1 / 2} \sim 2 \times 10^{24}

–

2 \times 10^{26}

years (90% C.L.) has been achieved. The present conservative upper limit on effective Majorana neutrino mass

⟨ m_{ν} ⟩

was established from these experiments as 0.16 eV (90% C.L.). The results of experiments on recording and studying the processes of two-neutrino double beta decay in various nuclei (transitions to both the ground and excited states of daughter nuclei) are discussed too. The results of experiments on the search for majoron are also given. Possible progress in this field in the future is discussed. 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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26 pages, 573 KiB

Open AccessArticle

Holographic Non-Abelian Flavour Symmetry Breaking

by Johanna Erdmenger, Nick Evans, Yang Liu and Werner Porod

Universe 2023, 9(6), 289; https://doi.org/10.3390/universe9060289 - 14 Jun 2023

Cited by 4 | Viewed by 838

Abstract

We investigate a holographic model for both spontaneous and explicit symmetry breaking of non-abelian flavour symmetries. This consists of a bottom-up model inspired by the top-down D3/probe D7-brane model. It incorporates the running anomalous dimensions of the fields. We ensure that in the [...] Read more.

We investigate a holographic model for both spontaneous and explicit symmetry breaking of non-abelian flavour symmetries. This consists of a bottom-up model inspired by the top-down D3/probe D7-brane model. It incorporates the running anomalous dimensions of the fields. We ensure that in the holographic bulk, the full non-abelian flavour symmetries for massless quarks are present. The quark masses are spontaneously generated field values in the bulk and there is a resultant bulk Higgs mechanism. We provide a numerical technique to find the mass eigenvalues from a system of mixed holographic fields, testing it against an analytic model of

N = 2

supersymmetric matter fields. We apply these ideas to two-flavour QCD with both

u - d

quark mass splitting and multi-trace bulk action terms that are expected to break U

{(N_{f})}_{V}

to SU(

N_{f})_{V} \times U {(1)}_{V}

away from large N. We also discuss three-flavour QCD with strange quark mass splitting and applications to more exotic symmetry breaking patterns of potential relevance for composite Higgs models. 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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43 pages, 594 KiB

Open AccessArticle

Maxwell-Dirac Isomorphism Revisited: From Foundations of Quantum Mechanics to Geometrodynamics and Cosmology

by Arkady L. Kholodenko

Universe 2023, 9(6), 288; https://doi.org/10.3390/universe9060288 - 12 Jun 2023

Viewed by 1462

Abstract

Although electrons (fermions)and photons (bosons) produce the same interference patterns in the two-slit experiments, known in optics for photons since the 17th Century, the description of these patterns for electrons and photons thus far was markedly different. Photons are spin one, relativistic and [...] Read more.

Although electrons (fermions)and photons (bosons) produce the same interference patterns in the two-slit experiments, known in optics for photons since the 17th Century, the description of these patterns for electrons and photons thus far was markedly different. Photons are spin one, relativistic and massless particles while electrons are spin half massive particles producing the same interference patterns irrespective to their speed. Experiments with other massive particles demonstrate the same kind of interference patterns. In spite of these differences, in the early 1930s of the 20th Century, the isomorphism between the source-free Maxwell and Dirac equations was established. In this work, we were permitted replace the Born probabilistic interpretation of quantum mechanics with the optical. In 1925, Rainich combined source-free Maxwell equations with Einstein’s equations for gravity. His results were rediscovered in the late 1950s by Misner and Wheeler, who introduced the word "geometrodynamics” as a description of the unified field theory of gravity and electromagnetism. An absence of sources remained a problem in this unified theory until Ranada’s work of the late 1980s. However, his results required the existence of null electromagnetic fields. These were absent in Rainich–Misner–Wheeler’s geometrodynamics. They were added to it in the 1960s by Geroch. Ranada’s solutions of source-free Maxwell’s equations came out as knots and links. In this work, we establish that, due to their topology, these knots/links acquire masses and charges. They live on the Dupin cyclides—the invariants of Lie sphere geometry. Symmetries of Minkowski space-time also belong to this geometry. Using these symmetries, Varlamov recently demonstrated group-theoretically that the experimentally known mass spectrum for all mesons and baryons is obtainable with one formula, containing electron mass as an input. In this work, using some facts from polymer physics and differential geometry, a new proof of the knotty nature of the electron is established. The obtained result perfectly blends with the description of a rotating and charged black hole. Full article

(This article belongs to the Section Mathematical Physics)

54 pages, 14340 KiB

Open AccessArticle

Deep Learning of Quasar Lightcurves in the LSST Era

by Andjelka B. Kovačević, Dragana Ilić, Luka Č. Popović, Nikola Andrić Mitrović, Mladen Nikolić, Marina S. Pavlović, Iva Čvorović-Hajdinjak, Miljan Knežević and Djordje V. Savić

Universe 2023, 9(6), 287; https://doi.org/10.3390/universe9060287 - 11 Jun 2023

Viewed by 1122

Abstract

Deep learning techniques are required for the analysis of synoptic (multi-band and multi-epoch) light curves in massive data of quasars, as expected from the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). In this follow-up study, we introduce an upgraded [...] Read more.

Deep learning techniques are required for the analysis of synoptic (multi-band and multi-epoch) light curves in massive data of quasars, as expected from the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). In this follow-up study, we introduce an upgraded version of a conditional neural process (CNP) embedded in a multi-step approach for the analysis of large data of quasars in the LSST Active Galactic Nuclei Scientific Collaboration data challenge database. We present a case study of a stratified set of u-band light curves for 283 quasars with very low variability ∼0.03. In this sample, the CNP average mean square error is found to be ∼5% (∼0.5 mag). Interestingly, besides similar levels of variability, there are indications that individual light curves show flare-like features. According to the preliminary structure–function analysis, these occurrences may be associated with microlensing events with larger time scales of 5–10 years. Full article

(This article belongs to the Special Issue A Multimessenger View of Supermassive Black Holes and the Quasar Main Sequence)

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17 pages, 1311 KiB

Open AccessArticle

Maxwell Field of a Charge in Hyperbolic Motion

by Ramón Serrano Montesinos and Juan Antonio Morales-Lladosa

Universe 2023, 9(6), 286; https://doi.org/10.3390/universe9060286 - 10 Jun 2023

Viewed by 896

Abstract

We conduct a detailed study of the electromagnetic field produced by a massive point particle undergoing hyperbolic (uniformly accelerated) motion in Minkowski space-time. Starting from the Liénard–Wiechert solution and using a covariant notation, we obtain and analyse the main quantities that describe this [...] Read more.

We conduct a detailed study of the electromagnetic field produced by a massive point particle undergoing hyperbolic (uniformly accelerated) motion in Minkowski space-time. Starting from the Liénard–Wiechert solution and using a covariant notation, we obtain and analyse the main quantities that describe this field. We identify the space-time region to which this solution is restricted and write a solution valid in the whole of space-time. Finally, we verify that this solution satisfies Maxwell’s equations in the sense of distributions. Full article

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

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14 pages, 1170 KiB

Open AccessArticle

Compact Stars in the vBag Model and Its f-Mode Oscillations

by Heng-Yi Zhou, Wei Wei and Xia Zhou

Universe 2023, 9(6), 285; https://doi.org/10.3390/universe9060285 - 10 Jun 2023

Viewed by 1111

Abstract

Electromagnetic (EM) observations and gravitational wave (GW) measurements enable us to determine the mass and radius of neutron stars (NSs) and their tidal deformability, respectively. These parameters offer valuable insights into the properties of dense matter in NSs. In this study, the vector-interaction-enhanced [...] Read more.

Electromagnetic (EM) observations and gravitational wave (GW) measurements enable us to determine the mass and radius of neutron stars (NSs) and their tidal deformability, respectively. These parameters offer valuable insights into the properties of dense matter in NSs. In this study, the vector-interaction-enhanced bag model (vBag model) is employed to investigate strange and hybrid stars’ properties. The parameters of the vBag model are constrained using multi-messenger observations, revealing that strange stars are incompatible with current observations. In contrast, hybrid stars can exhibit a substantial mixed phase region and a thin hadronic shell. Furthermore, we present the frequencies and damping time of fundamental mode (f-mode) oscillations of hybrid stars and test their universal relations with compactness and tidal deformability. The findings indicate that the presence of mixed phase components leads to larger frequencies and shorter damping time of the f-mode oscillation of hybrid stars, and the softer equation of state (EoS) affects this behavior more significantly. The universal relations of hybrid stars in the vBag model can be described by fourth-order/seventh-order polynomials, which do not break the previous results. Full article

(This article belongs to the Special Issue Studies in Neutron Stars)

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16 pages, 668 KiB

Open AccessFeature PaperArticle

Classical Mechanics with Inequality Constraints and Gravity Models with Limiting Curvature

by Andrei V. Frolov and Valeri P. Frolov

Universe 2023, 9(6), 284; https://doi.org/10.3390/universe9060284 - 10 Jun 2023

Viewed by 1189

Abstract

In this paper, we discuss mechanical systems with inequality constraints

Φ (q, \dot{q}, . . .) \leq 0

. We demonstrate how such constraints can be taken into account by proper modification of the action which describes the [...] Read more.

In this paper, we discuss mechanical systems with inequality constraints

Φ (q, \dot{q}, . . .) \leq 0

. We demonstrate how such constraints can be taken into account by proper modification of the action which describes the original unconstrained dynamics. To illustrate this approach, we consider a harmonic oscillator in the model with limiting velocity. We compare the behavior of such an oscillator with the behavior of a relativistic oscillator and demonstrate that when the amplitude of the oscillator is large, the properties of both types of oscillators are quite similar. We also discuss inequality constraints, which contain higher derivatives. At the end of the paper, we briefly discuss possible applications of the developed approach to gravity models with limiting curvature. Full article

(This article belongs to the Special Issue Quantum Physics including Gravity: Highlights and Novelties)

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14 pages, 1311 KiB

Open AccessArticle

Homogeneous Cosmological Models in Weyl’s Geometrical Scalar–Tensor Theory

by Adriano Barros and Carlos Romero

Universe 2023, 9(6), 283; https://doi.org/10.3390/universe9060283 - 10 Jun 2023

Cited by 1 | Viewed by 627

Abstract

In this paper, we consider homogeneous cosmological solutions in the context of the Weyl geometrical scalar–tensor theory. Firstly, we exhibit an anisotropic Kasner type solution taking advantage of some similarities between this theory and the Brans–Dicke theory. Next, we consider an isotropic model [...] Read more.

In this paper, we consider homogeneous cosmological solutions in the context of the Weyl geometrical scalar–tensor theory. Firstly, we exhibit an anisotropic Kasner type solution taking advantage of some similarities between this theory and the Brans–Dicke theory. Next, we consider an isotropic model with a flat spatial section sourced by matter configurations described by a perfect fluid. In this model, we obtain an analytical solution for the stiff matter case. For other cases, we carry out a complete qualitative analysis theory to investigate the general behaviour of the solutions, presenting some possible scenarios. In this work, we do not consider the presence of the cosmological constant nor do we take any potential of the scalar field into account. Because of this, we do not find any solution describing the acceleration of the universe. Full article

(This article belongs to the Section Cosmology)

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34 pages, 457 KiB

Open AccessArticle

A Variational Approach to Resistive General Relativistic Two-Temperature Plasmas

by Gregory Lee Comer, Nils Andersson, Thomas Celora and Ian Hawke

Universe 2023, 9(6), 282; https://doi.org/10.3390/universe9060282 - 09 Jun 2023

Viewed by 739

Abstract

We develop an action principle to construct the field equations for dissipative/resistive general relativistic two-temperature plasmas, including a neutrally charged component. The total action is a combination of four pieces: an action for a multifluid/plasma system with dissipation/resistivity and entrainment; the Maxwell action [...] Read more.

We develop an action principle to construct the field equations for dissipative/resistive general relativistic two-temperature plasmas, including a neutrally charged component. The total action is a combination of four pieces: an action for a multifluid/plasma system with dissipation/resistivity and entrainment; the Maxwell action for the electromagnetic field; the Coulomb action with a minimal coupling of the four-potential to the charged fluxes; and the Einstein–Hilbert action for gravity (with the metric being minimally coupled to the other action pieces). We use a pull-back formalism from spacetime to abstract matter spaces to build unconstrained variations for the neutral, positively, and negatively charged fluid species and for three associated entropy flows. The full suite of field equations is recast in the so-called “

3 + 1

” form (suitable for numerical simulations), where spacetime is broken up into a foliation of spacelike hypersurfaces and a prescribed “flow-of-time”. A previously constructed phenomenological model for the resistivity is updated to include the modified heat flow and the presence of a neutrally charged species. We impose baryon number and charge conservation as well as the Second Law of Thermodynamics in order to constrain the number of free parameters in the resistivity. Finally, we take the Newtonian limit of the “

3 + 1

” form of the field equations, which can be compared to existing non-relativistic formulations. Applications include main sequence stars, neutron star interiors, accretion disks, and the early universe. Full article

(This article belongs to the Section Gravitation)

19 pages, 355 KiB

Open AccessArticle

Henneaux–Teitelboim Gauge Symmetry and Its Applications to Higher Gauge Theories

by Mihailo Đorđević, Tijana Radenković, Pavle Stipsić and Marko Vojinović

Universe 2023, 9(6), 281; https://doi.org/10.3390/universe9060281 - 09 Jun 2023

Cited by 2 | Viewed by 668

Abstract

When discussing the gauge symmetries of any theory, the Henneaux–Teitelboim transformations are often underappreciated or even completely ignored, due to their on-shell triviality. Nevertheless, these gauge transformations play an important role in understanding the structure of the full gauge symmetry group of any [...] Read more.

When discussing the gauge symmetries of any theory, the Henneaux–Teitelboim transformations are often underappreciated or even completely ignored, due to their on-shell triviality. Nevertheless, these gauge transformations play an important role in understanding the structure of the full gauge symmetry group of any theory, especially regarding the subgroup of diffeomorphisms. We give a review of the Henneaux–Teitelboim transformations and the resulting gauge group in the general case and then discuss its role in the applications to the class of topological theories called nBF models, relevant for the constructions of higher gauge theories and quantum gravity. Full article

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

25 pages, 12536 KiB

Open AccessArticle

Modeling the Topside Ionosphere Effective Scale Height through In Situ Electron Density Observations by Low-Earth-Orbit Satellites

by Alessio Pignalberi, Michael Pezzopane, Tommaso Alberti, Igino Coco, Giuseppe Consolini, Giulia D’Angelo, Paola De Michelis, Fabio Giannattasio, Bruno Nava, Mirko Piersanti and Roberta Tozzi

Universe 2023, 9(6), 280; https://doi.org/10.3390/universe9060280 - 09 Jun 2023

Cited by 1 | Viewed by 867

Abstract

In this work, we aim to characterize the effective scale height at the ionosphere F2-layer peak (H₀) by using in situ electron density (N_e) observations by Langmuir Probes (LPs) onboard the China Seismo-Electromagnetic Satellite (CSES—01). CSES—01 is [...] Read more.

In this work, we aim to characterize the effective scale height at the ionosphere F2-layer peak (H₀) by using in situ electron density (N_e) observations by Langmuir Probes (LPs) onboard the China Seismo-Electromagnetic Satellite (CSES—01). CSES—01 is a sun-synchronous satellite orbiting at an altitude of ~500 km, with descending and ascending nodes at ~14:00 local time (LT) and ~02:00 LT, respectively. Calibrated CSES—01 LPs N_e observations for the years 2019–2021 provide information in the topside ionosphere, whereas the International Reference Ionosphere model (IRI) provides N_e values at the F2-layer peak altitude for the same time and geographical coordinates as CSES—01. CSES—01 and IRI N_e datasets are used as anchor points to infer H₀ by assuming a linear scale height in the topside representation given by the NeQuick model. COSMIC/FORMOSAT—3 (COSMIC—1) radio occultation (RO) data are used to constrain the vertical gradient of the effective scale height in the topside ionosphere in the linear approximation. With the CSES—01 dataset, we studied the global behavior of H₀ for daytime (~14:00 LT) and nighttime (~02:00 LT) conditions, different seasons, and low solar activity. Results from CSES—01 observations are compared with those obtained through Swarm B satellite N_e-calibrated measurements and validated against those from COSMIC—1 RO for similar diurnal, seasonal, and solar activity conditions. H₀ values modeled by using CSES—01 and Swarm B-calibrated observations during daytime both agree with corresponding values obtained directly from COSMIC—1 RO profiles. Differently, H₀ modeling for nighttime conditions deserves further investigation because values obtained from both CSES—01 and Swarm B-calibrated observations show remarkable and spatially localized differences compared to those obtained through COSMIC—1. Most of the H₀ mismodeling for nighttime conditions can probably to be attributed to a sub-optimal spatial representation of the F2-layer peak density made by the underlying IRI model. For comparison, H₀ values obtained with non-calibrated CSES—01 and Swarm B N_e observations are also calculated and discussed. The methodology developed in this study for the topside effective scale height modeling turns out to be applicable not only to CSES—01 satellite data but to any in situ N_e observation by low-Earth-orbit satellites orbiting in the topside ionosphere. Full article

(This article belongs to the Section Space Science)

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29 pages, 4268 KiB

Open AccessReview

The Central Engine of GRB170817A and the Energy Budget Issue: Kerr Black Hole versus Neutron Star in a Multi-Messenger Analysis

by Maurice H. P. M. van Putten

Universe 2023, 9(6), 279; https://doi.org/10.3390/universe9060279 - 08 Jun 2023

Cited by 2 | Viewed by 1174

Abstract

Upcoming LIGO–Virgo–KAGRA (LVK) observational runs offer new opportunities to probe the central engines of extreme transient events. Cosmological gamma-ray bursts (GRBs) and core-collapse supernovae (CC-SNe), in particular, are believed to be powered by compact objects, i.e., a neutron star (NS) or black hole [...] Read more.

Upcoming LIGO–Virgo–KAGRA (LVK) observational runs offer new opportunities to probe the central engines of extreme transient events. Cosmological gamma-ray bursts (GRBs) and core-collapse supernovae (CC-SNe), in particular, are believed to be powered by compact objects, i.e., a neutron star (NS) or black hole (BH). A principal distinction between an NS and BH is the energy reservoir in the angular momentum

E_{J}

. Per unit mass, this reaches a few percent in a rapidly rotating NS and tens of percent in a Kerr BH, respectively. Calorimetry by

E_{G W}

on a descending chirp may break the degeneracy between the two. We review this approach, anticipating new observational opportunities for planned LVK runs. GRB170817A is the first event revealing its central engine by a descending chirp in gravitational radiation. An accompanying energy output

E_{G W} ≃ 3.5 % M_{⊙} c^{2}

is observed during GRB170817A in the aftermath of the double neutron star merger GW170817. The progenitors of normal long GRBs, on the other hand, are the rare offspring of CC-SNe of type Ib/c. Yet, the extended emission to SGRBs (SGRBEEs) shares similar durations and the same Amati-relation of the prompt GRB emission of LGRBs, pointing to a common central engine. The central engine of these extreme transient events has, hitherto, eluded EM observations alone, even when including neutrino observations, as in SN1987A. The trigger signaling the birth of the compact object and the evolution powering these events is expected to be revealed by an accompanying GW signal, perhaps similar to that of GRB170817A. For GRB170817A,

E_{G W}

exceeds

E_{J}

in the initial hyper-massive neutron star (HMNS) produced in the immediate aftermath of GW170817. It identifies the spin-down of a Kerr BH of mass ∼

2.4 M_{⊙}

defined by the total mass of GW170817. This observation is realized in spectrograms generated by Butterfly matched filtering, a time-symmetric analysis with equal sensitivity to ascending and descending chirps, calibrated by signal injection experiments. It is implemented on a heterogeneous computing platform with synaptic parallel processing in F90/C++/C99 under bash. A statistical significance of

5.5 σ

is derived from multi-messenger event timing, based on a probability of false alarm (PFA) factored over a probability

p_{1} = 8.3 \times 10^{- 4}

by causality and a p-value

p_{2} = 4.9 \times 10^{- 5}

of consistency between H1 and L1 observations. For upcoming observations, this approach may be applied to similar emissions from SNIb/c and GRBs in the Local Universe, upon the mass-scaling of present results by the mass of their putative black hole-central engines. Full article

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

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16 pages, 3747 KiB

Open AccessArticle

A Wheeler–DeWitt Quantum Approach to the Branch-Cut Gravitation with Ordering Parameters

by Benno August Ludwig Bodmann, César Augusto Zen Vasconcellos, Peter Otto Hess Bechstedt, José Antonio de Freitas Pacheco, Dimiter Hadjimichef, Moisés Razeira and Gervásio Annes Degrazia

Universe 2023, 9(6), 278; https://doi.org/10.3390/universe9060278 - 08 Jun 2023

Cited by 5 | Viewed by 928

Abstract

In this contribution to the Festschrift for Prof. Remo Ruffini, we investigate a formulation of quantum gravity using the Hořava–Lifshitz theory of gravity, which is General Relativity augmented by counter-terms to render the theory regularized. We are then led to the Wheeler–DeWitt (WDW) [...] Read more.

In this contribution to the Festschrift for Prof. Remo Ruffini, we investigate a formulation of quantum gravity using the Hořava–Lifshitz theory of gravity, which is General Relativity augmented by counter-terms to render the theory regularized. We are then led to the Wheeler–DeWitt (WDW) equation combined with the classical concepts of the branch-cut gravitation, which contemplates as a new scenario for the origin of the Universe, a smooth transition region between the contraction and expansion phases. Through the introduction of an energy-dependent effective potential, which describes the space-time curvature associated with the embedding geometry and its coupling with the cosmological constant and matter fields, solutions of the WDW equation for the wave function of the Universe are obtained. The Lagrangian density is quantized through the standard procedure of raising the Hamiltonian, the helix-like complex scale factor of branched gravitation as well as the corresponding conjugate momentum to the category of quantum operators. Ambiguities in the ordering of the quantum operators are overcome with the introduction of a set of ordering factors

α

, whose values are restricted, to make contact with similar approaches, to the integers

α = [0, 1, 2]

, allowing this way a broader class of solutions for the wave function of the Universe. In addition to a branched universe filled with underlying background vacuum energy, primordial matter and radiation, in order to connect with standard model calculations, we additionally supplement this formulation with baryon matter, dark matter and quintessence contributions. Finally, the boundary conditions for the wave function of the Universe are imposed by assuming the Bekenstein criterion. Our results indicate the consistency of a topological quantum leap, or alternatively a quantum tunneling, for the transition region of the early Universe in contrast to the classic branched cosmology view of a smooth transition. Full article

(This article belongs to the Special Issue Remo Ruffini Festschrift)

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12 pages, 1567 KiB

Open AccessArticle

A Software for RFI Analysis of Radio Environment around Radio Telescope

by Yu Wang, Haiyan Zhang, Jian Wang, Shijie Huang, Hao Hu and Cheng Yang

Universe 2023, 9(6), 277; https://doi.org/10.3390/universe9060277 - 08 Jun 2023

Cited by 1 | Viewed by 944

Abstract

Radio astronomy uses radio telescopes to detect very faint emissions from celestial objects. However, human-made radio frequency interference (RFI) is currently a common problem faced by most terrestrial radio telescopes, and it is getting worse with the development of the economy and technology. [...] Read more.

Radio astronomy uses radio telescopes to detect very faint emissions from celestial objects. However, human-made radio frequency interference (RFI) is currently a common problem faced by most terrestrial radio telescopes, and it is getting worse with the development of the economy and technology. Therefore, it is essential to monitor and evaluate interference during the planning, construction, and operation stages of the radio telescope and protect the quiet radio environment around the radio astronomical site. In this paper, we present a software for an RFI analysis of the radio environment around the telescope. In this software, information has been collected, including the location of the site; the technical specifications, such as aperture and the frequency range of the radio telescopes; and the terrain around the site. The software and its modules are composed of telescope, geographic, and meteorological databases, and analysis modules of terrestrial and space-based RFI. Combined with the propagation characteristics of radio waves, we can analyze and evaluate RFI on the ground and in space around the radio telescope. The feasibility of the software has been proved by the experimental implementation of the propagation properties and RFI source estimation. With this software, efficient technical support can be expected for protecting the radio environment around the telescope, as well as improving site selection for planned radio astronomical facilities. Full article

(This article belongs to the Special Issue New Discoveries in Astronomical Data)

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16 pages, 579 KiB

Open AccessArticle

QCD Phase Structure and In-Medium Modifications of Meson Masses in Polyakov Linear-Sigma Model with Finite Isospin Asymmetry

by Abdel Nasser Tawfik

Universe 2023, 9(6), 276; https://doi.org/10.3390/universe9060276 - 08 Jun 2023

Cited by 2 | Viewed by 699

Abstract

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (

{\bar{σ}}_{3} = f_{K^{\pm}} - f_{K^{0}}

) and the third generator of the matrix of the explicit symmetry breaking [ [...] Read more.

In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (

{\bar{σ}}_{3} = f_{K^{\pm}} - f_{K^{0}}

) and the third generator of the matrix of the explicit symmetry breaking [

h_{3} = m_{a_{0}}^{2} (f_{K^{\pm}} - f_{K^{0}})

] are estimated in terms of the decay constants of the neutral (

f_{K}^{0}

) and charged Kaon (

f_{K^{\pm}}

) and the mass of

a_{0}

meson. Both quantities

{\bar{σ}}_{3}

and

h_{3}

are then evaluated, at finite baryon (

μ_{B}

), isospin chemical potential (

μ_{I}

), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (

T - μ_{I}

) phase diagram In the QCD-like effective model, the Polyakov linear-sigma model, the isospin sigma field (

{\bar{σ}}_{3} = f_{K^{\pm}} - f_{K^{0}}

) and the third generator of the matrix of the explicit symmetry breaking [

h_{3} = m_{a_{0}}^{2} (f_{K^{\pm}} - f_{K^{0}})

] are estimated in terms of the decay constants of the neutral (

f_{K}^{0}

) and charged Kaon (

f_{K^{\pm}}

) and the mass of

a_{0}

meson. Both quantities

{\bar{σ}}_{3}

and

h_{3}

are then evaluated, at finite baryon (

μ_{B}

), isospin chemical potential (

μ_{I}

), and temperature (T). Thereby, the dependence of the critical temperature on isospin chemical potential could be mapped out in the (

T - μ_{I}

) phase diagram. The in-medium modifications of pseudoscalars (

J^{p c} = 0^{- +}

), scalars (

J^{p c} = 0^{+ +}

), vectors (

J^{p c} = 1^{- -}

), and axial-vectors (

J^{p c} = 1^{+ +}

) meson states are then analyzed in thermal and dense medium. We conclude that the QCD phase diagram (

T - μ_{I}

) is qualitatively similar to the (

T - μ_{B}

) phase diagram. We also conclude that both temperature and isospin chemical potential enhance the in-medium modifications of the meson states

a_{0}

,

σ

,

η^{'}

,

π

,

f_{0}

,

κ

,

η

, K,

ρ

,

ω

,

κ^{*}

,

ϕ

,

a_{1}

,

f_{1}

,

K^{*}

, and

f_{1}^{*}

. Regarding their chemical potential, at high temperatures the various meson states likely dissolve into colored partonic phase. In this limit, the meson masses form a universal bundle. Thus, we conclude that the increase in the chemical potential similar to temperature derives the colorless confined meson states into the colored deconfined parton phase. 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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7 pages, 238 KiB

Open AccessCommunication

The Neutrino Mass Problem: From Double Beta Decay to Cosmology

by Osvaldo Civitarese

Universe 2023, 9(6), 275; https://doi.org/10.3390/universe9060275 - 07 Jun 2023

Cited by 1 | Viewed by 706

Abstract

The neutrino is perhaps the most elusive member of the particle zoo. The questions about its nature, namely: Dirac or Majorana, the value of its mass and the interactions with other particles, the number of its components including sterile species, are long standing [...] Read more.

The neutrino is perhaps the most elusive member of the particle zoo. The questions about its nature, namely: Dirac or Majorana, the value of its mass and the interactions with other particles, the number of its components including sterile species, are long standing ones and still remain to a large extent without conclusive answers. From the side of the nuclear structure and nuclear reactions, both theories and experiments, the need to elucidate these questions has, and still has, prompt crucial developments in the fields of double beta decay, double charge exchange and neutrino induced reactions. The measurements of neutrino flavor oscillation parameters contribute largely to restrict models with massless neutrinos. From the particle physics side, the possibilities to extend the standard model of electroweak interactions to incorporate a right-handed sector of the electroweak Lagrangian are directly linked to the adopted neutrino model. Here, I would like to address another aspect of the problem by asking the question of the neutrino mass mechanism in the cosmological context, and particularly about dark matter. 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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18 pages, 2936 KiB

Open AccessArticle

A Novel, Low-Cost, Position-Sensitive Neutron Detector to Support Thick-Target Inverse Kinematics Experiments for Nuclear Data Measurements

by R. Smith, J. P. Stowell, D. Barker and L. F. Thompson

Universe 2023, 9(6), 274; https://doi.org/10.3390/universe9060274 - 06 Jun 2023

Viewed by 931

Abstract

High quality nuclear data lie at the heart of accurately modelling stellar systems and terrestrial nuclear reactors. However, some key reaction cross sections have large uncertainties, which limit such models in predicting isotopic abundances and other aspects of stellar evolution, along with key [...] Read more.

High quality nuclear data lie at the heart of accurately modelling stellar systems and terrestrial nuclear reactors. However, some key reaction cross sections have large uncertainties, which limit such models in predicting isotopic abundances and other aspects of stellar evolution, along with key operational parameters for nuclear reactors. Reactions involving neutrons are particularly difficult to measure experimentally in laboratories, not least due to the unique challenges involved when detecting neutrons. We present a new approach to measuring nuclear reactions involving neutrons by exploiting the Thick-Target Inverse Kinematics (TTIK) approach. For such measurements, a new detector called ATTIKUS (A Thick-Target Inverse Kinematics detector by Universities in Sheffield) is under construction. Here we present designs and Geant4 Monte-Carlo simulations of the detector. The simulations indicate that a neutron position reconstruction resolution of 10 cm is obtainable and demonstrate how this device could be applied to the ¹³C(α,n) reaction, which is considered to be the main neutron source for the s-process in low-mass Asymptotic Giant Branch stars. In the TTIK method, the emission position of the neutron (the nuclear interaction position in a gaseous target) is directly linked to the centre-of-mass energy of the reaction. Therefore, a position resolution will translate into an energy resolution, depending on the beam-target combination. The inverse reaction, ¹⁶O(n,α), causes a large uncertainty in calculating the effective neutron multiplication factor, K_eff in nuclear reactors, so improvements are required here. Full article

(This article belongs to the Special Issue Advances in Cosmology and Subatomic Particle Physics)

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20 pages, 1972 KiB

Open AccessReview

The Zoo of Isolated Neutron Stars

by Sergei B. Popov

Universe 2023, 9(6), 273; https://doi.org/10.3390/universe9060273 - 06 Jun 2023

Cited by 4 | Viewed by 1028

Abstract

In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. [...] Read more.

In this brief review, I summarize our basic knowledge about different types of isolated neutron stars. I discuss radio pulsars, central compact objects in supernova remnants, magnetars, nearby cooling neutron stars (also known as the magnificent seven), and sources of fast radio bursts. Several scenarios of magneto-rotational evolution are presented. Recent observational data, such as the discovery of long-period radio pulsars, require the non-trivial evolution of magnetic fields, the spin periods of neutron stars, or both. In some detail, I discuss different models of magnetic field decay and interactions of young neutron stars with fallback matter. 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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41 pages, 519 KiB

Open AccessEditor’s ChoiceReview

The Warm Inflation Story

by Arjun Berera

Universe 2023, 9(6), 272; https://doi.org/10.3390/universe9060272 - 06 Jun 2023

Cited by 10 | Viewed by 1136

Abstract

Warm inflation has normalized two ideas in cosmology, that in the early universe the initial primordial density perturbations generally could be of classical rather than quantum origin and that during inflation, particle production from interactions amongst quantum field, and its backreaction effects, can [...] Read more.

Warm inflation has normalized two ideas in cosmology, that in the early universe the initial primordial density perturbations generally could be of classical rather than quantum origin and that during inflation, particle production from interactions amongst quantum field, and its backreaction effects, can occur concurrent with inflationary expansion. When we first introduced these ideas, both were met with resistance, but today they are widely accepted as possibilities with many models and applications based on them, which is an indication of the widespread influence of warm inflation. Open quantum field theory, which has been utilized in studies of warm inflation, is by now a relevant subject in cosmology, in part due to this early work. In this review I first discuss the basic warm inflation dynamics. I then outline how to compute warm inflation dynamics from first-principles quantum field theory (QFT) and in particular how a dissipative term arises. Warm inflation models can have an inflaton mass bigger than the Hubble scale and the inflaton field excursion can remain sub-Planckian, thus overcoming the most prohibitive problems of inflation model building. I discuss the early period of my work in developing warm inflation that helped me arrive at these important features of its dynamics. Inflationary cosmology today is immersed in hypothetical models, which by now are acting as a diversion from reaching any endgame in this field. I discuss better ways to approach model selection and give necessary requirements for a well constrained and predictive inflation model. A few warm inflation models are pointed out that could be developed to this extent. I discuss how, at this stage, more progress would be made in this subject by taking a broader view on the possible early universe solutions that include not just inflation but the diverse range of options. Full article

(This article belongs to the Special Issue Warm Inflation)

9 pages, 702 KiB

Open AccessArticle

Recurrent Large Sunspot Structures and 27-Day Component of Solar Activity as Proxies to Axis-Nonsymmetry

by Alexander Shapoval and Mikhail Shnirman

Universe 2023, 9(6), 271; https://doi.org/10.3390/universe9060271 - 05 Jun 2023

Viewed by 797

Abstract

The purpose of this paper is to design tools that quantify the structure of the nonsymmetrical component of the solar magnetic field. With the Fourier transform and the machine learning identification of recurrent objects, we define the 27-day component of solar proxies and [...] Read more.

The purpose of this paper is to design tools that quantify the structure of the nonsymmetrical component of the solar magnetic field. With the Fourier transform and the machine learning identification of recurrent objects, we define the 27-day component of solar proxies and recurrent large sunspot structures (ReLaSS), respectively. These two closely related characteristics are established to represent different components of the asymmetry of the solar magnetic field. We derive that the 27-day component and ReLaSS have anticorrelated since 1970 after dozens of years of a strong correlation. The persistence of the correlation sign during few solar cycles reflects yet unknown regularities of solar activity. The contribution of both proxies to the nonsymmetry of solar activity is shown to be lower in 1990–2010 than ∼100 years earlier. This property may be the trace of the asymmetry at the scales that are longer than the centennial Gleissberg cycle. Full article

(This article belongs to the Section Solar System)

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13 pages, 613 KiB

Open AccessArticle

Ordinary Muon Capture on ¹³⁶Ba: Comparative Study Using the Shell Model and pnQRPA

by Patricia Gimeno, Lotta Jokiniemi, Jenni Kotila, Marlom Ramalho and Jouni Suhonen

Universe 2023, 9(6), 270; https://doi.org/10.3390/universe9060270 - 05 Jun 2023

Cited by 3 | Viewed by 1028

Abstract

In this work, we present a study of ordinary muon capture (OMC) on

^{136}

Ba, the daughter nucleus of

^{136}

Xe double beta decay (DBD). The OMC rates at low-lying nuclear states (below 1 MeV of excitation energy) in

^{136}

Cs are assessed [...] Read more.

In this work, we present a study of ordinary muon capture (OMC) on

^{136}

Ba, the daughter nucleus of

^{136}

Xe double beta decay (DBD). The OMC rates at low-lying nuclear states (below 1 MeV of excitation energy) in

^{136}

Cs are assessed by using both the interacting shell model (ISM) and proton–neutron quasiparticle random-phase approximation (pnQRPA). We also add chiral two-body (2BC) meson-exchange currents and use an exact Dirac wave function for the captured s-orbital muon. OMC can be viewed as a complementary probe of the wave functions in

^{136}

Cs, the intermediate nucleus of the

^{136}

Xe DBD. At the same time, OMC can be considered a powerful probe of the effective values of weak axial-type couplings in a 100 MeV momentum exchange region, which is relevant for neutrinoless DBD. The present work represents the first attempt to compare the ISM and pnQRPA results for OMC on a heavy nucleus while also including the exact muon wave function and the 2BC. The sensitivity estimates of the current and future neutrinoless DBD experiments will clearly benefit from future OMC measurements taken using OMC calculations similar to the one presented here. 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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3 pages, 174 KiB

Open AccessEditorial

Editorial for the Special Issue “Torsion-Gravity and Spinors in Fundamental Theoretical Physics”

by Luca Fabbri

Universe 2023, 9(6), 269; https://doi.org/10.3390/universe9060269 - 04 Jun 2023

Viewed by 839

Abstract

The Einsteinian theory of gravitation is among the best-established theories ever conceived in physics [...] Full article

(This article belongs to the Special Issue Torsion-Gravity and Spinors in Fundamental Theoretical Physics)

12 pages, 827 KiB

Open AccessEssay

Finding My Drumbeat: Applying Lessons Learned from Remo Ruffini to Understanding Astrophysical Transients

by Chris Fryer

Universe 2023, 9(6), 268; https://doi.org/10.3390/universe9060268 - 04 Jun 2023

Viewed by 745

Abstract

As with many fields from fashion to politics, science is susceptible to “bandwagon”-driven research where an idea becomes increasingly popular, garnering a growing amount of “scientific” support. Bandwagons allow scientists to converge on a solution, but when the prevailing bandwagon is incorrect or [...] Read more.

As with many fields from fashion to politics, science is susceptible to “bandwagon”-driven research where an idea becomes increasingly popular, garnering a growing amount of “scientific” support. Bandwagons allow scientists to converge on a solution, but when the prevailing bandwagon is incorrect or too simple, this rigid mentality makes it very difficult for scientists to find the right track. True scientific innovation often occurs through scientists willing to march to the beat of their own drum. Using examples in the field of astrophysical transients, this paper demonstrates the importance of supporting scientists in their quest to develop their own personal drumbeat. Full article

(This article belongs to the Special Issue Remo Ruffini Festschrift)

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