Universe

22 pages, 495 KiB

Open AccessArticle

The Theoretical Description of the Transverse Momentum Spectra: A Unified Model

by Rohit Gupta, Anjaly Menon, Shubhangi Jain and Satyajit Jena

Universe 2023, 9(2), 111; https://doi.org/10.3390/universe9020111 - 20 Feb 2023

Cited by 1 | Viewed by 1100

Analysis of transverse momentum distributions is a useful tool to understand the dynamics of relativistic particles produced in high-energy collisions. Finding a proper distribution function to approximate the spectra is a vastly developing area of research in particle physics. In this work, we [...] Read more.

Analysis of transverse momentum distributions is a useful tool to understand the dynamics of relativistic particles produced in high-energy collisions. Finding a proper distribution function to approximate the spectra is a vastly developing area of research in particle physics. In this work, we have provided a detailed theoretical description of the unified statistical framework in high-energy physics. We have tested the applicability of this framework on experimental data by analyzing the transverse momentum spectra of pion produced in heavy-ion collision at RHIC and LHC. We have also attempted to explain the transverse momentum spectra of charged hadrons formed in pp collision at different energies using the unified statistical framework. This formalism has been proved to nicely explain the spectra of particles produced in soft processes as well as hard scattering processes in a consistent manner. Full article

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

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12 pages, 270 KiB

Open AccessArticle

Curvature Dynamics in General Relativity

by Jan W. van Holten

Universe 2023, 9(2), 110; https://doi.org/10.3390/universe9020110 - 20 Feb 2023

Cited by 2 | Viewed by 732

Abstract

The equations of general relativity are recast in the form of a wave equation for the Weyl tensor. This allows reformulation of gravitational wave theory in terms of curvature waves, rather than metric waves. The existence of two transverse polarization states for curvature [...] Read more.

The equations of general relativity are recast in the form of a wave equation for the Weyl tensor. This allows reformulation of gravitational wave theory in terms of curvature waves, rather than metric waves. The existence of two transverse polarization states for curvature waves is proven and in the linearized approximation the quadrupole formula is rederived. A perturbative scheme to extend the linearized result to the non-linear regime is outlined. Full article

(This article belongs to the Section Gravitation)

19 pages, 812 KiB

Open AccessArticle

On the η₁(1855), π₁(1400) and π₁(1600) as Dynamically Generated States and Their SU(3) Partners

by Mao-Jun Yan, Jorgivan M. Dias, Adolfo Guevara, Feng-Kun Guo and Bing-Song Zou

Universe 2023, 9(2), 109; https://doi.org/10.3390/universe9020109 - 19 Feb 2023

Cited by 3 | Viewed by 1301

Abstract

In this work, we interpret the newly observed

η_{1} (1855)

resonance with exotic

J^{P C} = 1^{- +}

quantum numbers in the

I = 0

sector, reported by the BESIII Collaboration, as a dynamically generated state from the [...] Read more.

In this work, we interpret the newly observed

η_{1} (1855)

resonance with exotic

J^{P C} = 1^{- +}

quantum numbers in the

I = 0

sector, reported by the BESIII Collaboration, as a dynamically generated state from the interaction between the lightest pseudoscalar mesons and axial-vector mesons. The interaction is derived from the lowest order chiral Lagrangian from which the Weinberg–Tomozawa term is obtained, describing the transition amplitudes among the relevant channels, which are then unitarized using the Bethe–Salpeter equation, according to the chiral unitary approach. We evaluate the

η_{1} (1855)

decays into the

η η^{'}

and

K {\bar{K}}^{*} π

channels and find that the latter has a larger branching fraction. We also investigate its SU(3) partners, and according to our findings, the

π_{1} (1400)

and

π_{1} (1600)

structures may correspond to dynamically generated states, with the former one coupled mostly to the

b_{1} π

component and the latter one coupled to the

K_{1} (1270) \bar{K}

channel. In particular, our result for the ratio

Γ (π_{1} (1600) \to f_{1} (1285) π) / Γ (π_{1} (1600) \to η^{'} π)

is consistent with the measured value, which supports our interpretation for the higher

π_{1}

state. We also report two poles with a mass about 1.7 GeV in the

I = 1 / 2

sector, which may be responsible for the

K^{*} (1680)

. We suggest searching for two additional

η_{1}

exotic mesons with masses around 1.4 and 1.7 GeV. In particular, the predicted

η_{1} (1700)

is expected to have a width around 0.1 GeV and can decay easily into

K \bar{K} π π

. Full article

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

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16 pages, 512 KiB

Open AccessArticle

Fermionic Greybody Factors in Schwarzschild Acoustic Black Holes

by Sara Kanzi and İzzet Sakallı

Universe 2023, 9(2), 108; https://doi.org/10.3390/universe9020108 - 19 Feb 2023

Cited by 1 | Viewed by 1022

Abstract

In Schwarzschild acoustic black hole (SABH) spacetime, we investigate the wave dynamics for the fermions. To this end, we first take into account the Dirac equation in the SABH by employing a null tetrad in the Newman–Penrose (NP) formalism. Then, we consider the [...] Read more.

In Schwarzschild acoustic black hole (SABH) spacetime, we investigate the wave dynamics for the fermions. To this end, we first take into account the Dirac equation in the SABH by employing a null tetrad in the Newman–Penrose (NP) formalism. Then, we consider the Dirac and Rarita–Schwinger equations, respectively. The field equations are reduced to sets of radial and angular equations. By using the analytical solution of the angular equation set, we decouple the radial wave equations and obtain the one-dimensional Schrödinger-like wave equations with their effective potentials. The obtained effective potentials are graphically depicted and analyzed. Finally, we investigate the fermionic greybody factors (GFs) radiated by the SABH spacetime. A thorough investigation is conducted into how the acoustic tuning parameter affects the GFs of the SABH spacetime. Both the semi-analytic WKB method and bounds for the GFs are used to produce the results, which are shown graphically and discussed. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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9 pages, 339 KiB

Open AccessCommunication

Beam Energy Dependence of the Linear and Mode-Coupled Flow Harmonics Using the a Multi-Phase Transport Model

by Niseem Magdy

Universe 2023, 9(2), 107; https://doi.org/10.3390/universe9020107 - 18 Feb 2023

Cited by 2 | Viewed by 683

Abstract

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic (

v_{4}

) and the mode-coupled response coefficient as functions of centrality in [...] Read more.

In the framework of the A Multi-Phase Transport (AMPT) model, the multi-particle azimuthal cumulant method is used to calculate the linear and mode-coupled contributions to the quadrangular flow harmonic (

v_{4}

) and the mode-coupled response coefficient as functions of centrality in Au+Au collisions at

\sqrt{s_{N N}}

= 200, 39, 27 and 19.6 GeV. This study indicates that the linear and mode-coupled contributions to

v_{4}

are sensitive to beam energy change. Nevertheless, the correlations between different-order flow symmetry planes and the mode-coupled response coefficients show weak beam energy dependence. In addition, the presented results suggest that the experimental measurements that span a broad range of beam energies can be an additional constraint for the theoretical model calculations. Full article

(This article belongs to the Special Issue Intermediate-Energy Heavy-Ion Collisions and Studies with Transport Models)

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11 pages, 494 KiB

Open AccessArticle

Diagram of High-Energy Nuclear Collisions

by Evgeny Andronov, Magdalena Kuich and Marek Gazdzicki

Universe 2023, 9(2), 106; https://doi.org/10.3390/universe9020106 - 18 Feb 2023

Cited by 2 | Viewed by 1034

Abstract

Many new particles, mostly hadrons, are produced in high-energy collisions between atomic nuclei. The most popular models describing the hadron-production process are based on the creation, evolution and decay of resonances, strings or quark–gluon plasma. The validity of these models is under vivid [...] Read more.

Many new particles, mostly hadrons, are produced in high-energy collisions between atomic nuclei. The most popular models describing the hadron-production process are based on the creation, evolution and decay of resonances, strings or quark–gluon plasma. The validity of these models is under vivid discussion, and it seems that a common framework for this discussion is missing. Here, for the first time, we explicitly introduce the diagram of high-energy nuclear collisions, where domains of the dominance of different hadron-production processes in the space of laboratory-controlled parameters, the collision energy and nuclear-mass number of colliding nuclei are indicated. We argue that the recent experimental results suggest the location of boundaries between the domains, allowing for the first time to sketch an example diagram. Finally, we discuss the immediate implications for experimental measurements and model development following the proposed sketch of the diagram. Full article

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

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10 pages, 287 KiB

Open AccessPerspective

Kilonova Emission and Heavy Element Nucleosynthesis

by Elena Pian

Universe 2023, 9(2), 105; https://doi.org/10.3390/universe9020105 - 17 Feb 2023

Cited by 3 | Viewed by 1315

Abstract

The binary neutron star merger observed and localized on 17 August 2017 by the LIGO and Virgo gravitational interferometers and by numerous telescopes on the ground and in orbit linked in an unambiguous way the coalescence of double neutron stars with the formation [...] Read more.

The binary neutron star merger observed and localized on 17 August 2017 by the LIGO and Virgo gravitational interferometers and by numerous telescopes on the ground and in orbit linked in an unambiguous way the coalescence of double neutron stars with the formation of a relativistic outflow (short gamma-ray burst GRB170817A) and of a thermal radioactive source (kilonova). The vicinity of the event (40 Mpc) made it possible to monitor the electromagnetic counterpart in detail at all wavelengths and to map its close environment in the outskirts of the lenticular galaxy NGC 4993. Radio VLBI images of GRB170817A allowed the first direct detection of superluminal motion in a GRB afterglow, pointing to a collimated ultra-relativistic jet rather than to a quasi-isotropically, mildly relativistically expanding source. The accurate spectroscopy of the kilonova at ultraviolet-to-infrared wavelengths with the X-Shooter spectrograph of the ESO Very Large Telescope showed the long-sought-after signature of rapid neutron capture process (in short: r-process) nucleosynthesis. Kilonova detection makes gravitational wave sources optimal tracers of heavy element formation sites. Full article

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

11 pages, 710 KiB

Open AccessArticle

Holographic p-Wave Superconductor with Excited States in 4D Einstein–Gauss–Bonnet Gravity

by Dong Wang, Xinyi Du, Qiyuan Pan and Jiliang Jing

Universe 2023, 9(2), 104; https://doi.org/10.3390/universe9020104 - 17 Feb 2023

Cited by 1 | Viewed by 1034

Abstract

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to [...] Read more.

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to be formed in the full parameter space, which is different from the holographic s-wave superconductor. Regardless of the choice of the vector mass by selecting the value of

m^{2} L^{2}

or

m^{2} L_{eff}^{2}

, we note that the critical chemical potential becomes evenly spaced for the number of nodes and that the difference of the critical chemical potential between the consecutive states depends on the curvature correction. Moreover, we find that the higher curvature correction or the higher excited state will alter the universal relation of the gap frequency, and the pole and delta function of the conductivity for the excited states can be broadened into the peaks with the finite width as the curvature correction increases. Full article

(This article belongs to the Special Issue Black Holes in Einstein–Gauss–Bonnet Theories)

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17 pages, 329 KiB

Open AccessArticle

Cosmological Constant from Boundary Condition and Its Implications beyond the Standard Model

by Jan O. Stenflo

Universe 2023, 9(2), 103; https://doi.org/10.3390/universe9020103 - 17 Feb 2023

Viewed by 1488

Abstract

Standard cosmology has long been plagued by a number of persistent problems. The origin of the apparent acceleration of the cosmic expansion remains enigmatic. The cosmological constant has been reintroduced as a free parameter with a value in energy density units that “happens” [...] Read more.

Standard cosmology has long been plagued by a number of persistent problems. The origin of the apparent acceleration of the cosmic expansion remains enigmatic. The cosmological constant has been reintroduced as a free parameter with a value in energy density units that “happens” to be of the same order as the present matter energy density. There is an internal inconsistency with regards to the Hubble constant, the so-called

H_{0}

tension. The derived value of

H_{0}

depends on the type of data that is used. With supernovae as standard candles, one gets a

H_{0}

that is 4–5

σ

larger than the value that one gets from CMB (Cosmic Microwave Background) data for the early universe. Here we show that these problems are related and can be solved if the cosmological constant represents a covariant integration constant that arises from a spatial boundary condition, instead of being a new type of hypothetical physical field, “dark energy”, as assumed by standard cosmology. The boundary condition only applies to the bounded 3D subspace that represents the observable universe, the hypersurface of the past light cone. Full article

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

14 pages, 4072 KiB

Open AccessArticle

An Empirical Orthogonal Function Study of the Ionospheric TEC Predicted Using the TIEGCM Model over the South Atlantic Anomaly in 2002 and 2008

by Jing Yu, Zheng Li, Yan Wang, Jingjing Shao, Luyao Wang, Jingyuan Li, Hua Zhang, Xiaojun Xu and Chunli Gu

Universe 2023, 9(2), 102; https://doi.org/10.3390/universe9020102 - 16 Feb 2023

Cited by 2 | Viewed by 1129

Abstract

In this study, the variability of the ionospheric total electron content (TEC) in the South Atlantic Anomaly (SAA) in the solar maximum of 2002 and the solar minimum of 2008 were compared by using an empirical orthogonal function (EOF) analysis. The ionospheric TEC [...] Read more.

In this study, the variability of the ionospheric total electron content (TEC) in the South Atlantic Anomaly (SAA) in the solar maximum of 2002 and the solar minimum of 2008 were compared by using an empirical orthogonal function (EOF) analysis. The ionospheric TEC data were simulated using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The first three EOFs accounted for 94.8% and 93.86% of the variability in the data in 2002 and 2008, respectively. The results showed that the TEC variations of the first three EOFs were generally consistent in 2002 and 2008. The first mode showed the equatorial anomaly caused by plasma drift and the east–west asymmetry possibly caused by the change in geomagnetic declination and zonal wind; EOF₂ exhibited the zonal variation influenced by the solar EUV radiation and the semiannual variation possibly controlled by the [O/N₂], solar zenith angle, and atmospheric circulation. EOF₃ suggested an equatorial anomaly and winter anomaly influenced by the [O/N₂] variation. However, the values and amplitude variations in the TEC were significantly greater in the solar maximum than that in the solar minimum, and the spring–autumn asymmetry of the TEC was more obvious in the solar minimum. In addition, we used the EOF method to extract the annual variation characteristics of the time coefficients and carried out a correlation analysis. The results showed that the annual variation in the TEC in 2002 was mainly affected by the solar EUV radiation, which was strongly correlated with F10.7 (r = 0.7348). In contrast, the TEC was mainly influenced by the geomagnetic activity in 2008 and had a strong correlation with Dst (r = −0.7898). Full article

(This article belongs to the Section Space Science)

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22 pages, 337 KiB

Open AccessArticle

On the Role of Constraints and Degrees of Freedom in the Hamiltonian Formalism

by Alexey Golovnev

Universe 2023, 9(2), 101; https://doi.org/10.3390/universe9020101 - 16 Feb 2023

Cited by 12 | Viewed by 960

Abstract

Unfortunately, the Hamiltonian mechanics of degenerate Lagrangian systems is usually presented as a mere recipe of Dirac, with no explanation as to how it works. It then comes to discussing conjectures of whether all primary constraints correspond to gauge symmetries, and it goes [...] Read more.

Unfortunately, the Hamiltonian mechanics of degenerate Lagrangian systems is usually presented as a mere recipe of Dirac, with no explanation as to how it works. It then comes to discussing conjectures of whether all primary constraints correspond to gauge symmetries, and it goes all the way to absolutely wrong claims such as the statement that electrodynamics or gravity only have two physical components each, with others being spurious. One has to be very careful because non-dynamical, or constrained, does not mean unphysical. In this article, I give a pedagogical introduction to the degenerate Hamiltonian systems, showing both very simple mechanical examples and general arguments about how it works. For the familiar field theory models, I explain why the gauge freedom there “hits twice” in the sense of producing twice as many first-class constraints as gauge symmetries, and why primary, and only primary, constraints should be put into the total Hamiltonian. Full article

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

15 pages, 467 KiB

Open AccessArticle

Reconstructing Torsion Cosmology from Interacting Holographic Dark Energy Model

by Song Li and Yun Chen

Universe 2023, 9(2), 100; https://doi.org/10.3390/universe9020100 - 16 Feb 2023

Viewed by 1004

Abstract

We consider a cosmological model in the framework of Einstein–Cartan theory with a single scalar torsion

ϕ = ϕ (t)

and reconstruct the torsion model corresponding to the holographic dark energy (HDE) density. By studying the corresponding relation between the effective [...] Read more.

We consider a cosmological model in the framework of Einstein–Cartan theory with a single scalar torsion

ϕ = ϕ (t)

and reconstruct the torsion model corresponding to the holographic dark energy (HDE) density. By studying the corresponding relation between the effective energy density of torsion field

ρ_{ϕ}

and holographic dark energy density

ρ_{H D E}

, we naturally obtain a kind of torsion field from the interacting holographic dark energy with interaction term

Q = - 2 ϕ ρ_{m}

and

ρ_{m}

is the energy density of matter. We analyze the reconstructed torsion model and find that the torsion field behaves like the quintessence

(w > - 1)

or quintom (exhibiting a transition from

w > - 1

to

w < - 1

) dark energy, depending on the value of the model parameter c. We then perform a stability analysis according to the squared sound speed. It is shown that the model is classically stable in the current epoch for the case of

c < 1

. We also investigate the model from the viewpoint of statefinder parameters and it turns out that the statefinder trajectories in the

r - s

plane behave differently for the three cases of c and also quite distinct from those of other cosmological models. From the trajectories of the statefinder pair

{q, r}

, we find that, for all the three cases of c, the universe has a phase transition from deceleration to acceleration, consistently with cosmological observations. In addition, we fit the reconstructed torsion model with the recent Type Ia supernovae (SNe Ia) samples, i.e., the Pantheon sample containing 1048 SNe Ia with the redshift in the range

0.01 < z < 2.3

and the Pantheon+ sample with 1701 light curves of 1550 distinct SNe Ia in the range

0.001 < z < 2.26

. The analysis results show that the limits on the present fractional energy density of matter

Ω_{m 0}

are completely compatible with those of the

Λ

CDM model obtained from the latest Planck mission observations at 68% confidence level. The mean value of c constrained from the Pantheon sample corresponds to the quintom-like scenario (i.e.,

c < 1

) and its mean value from the Pantheon+ sample corresponds to the quintessence-like scenario (i.e.,

c \geq 1

). However, both of the Pantheon and Pantheon+ samples cannot distinguish the quintom-like and quintessence-like scenarios at 68% confidence level. Full article

(This article belongs to the Special Issue Quantum Entanglement and Holographic Universe)

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17 pages, 485 KiB

Open AccessArticle

Theoretical Arguments and Experimental Signals for a Second Resonance of the Higgs Field

by Maurizio Consoli, Leonardo Cosmai and Fabrizio Fabbri

Universe 2023, 9(2), 99; https://doi.org/10.3390/universe9020099 - 15 Feb 2023

Cited by 2 | Viewed by 909

Abstract

Theoretical arguments and lattice simulations suggest that, beside the known resonance of mass

m_{h} =

125 GeV, the Higgs field could exhibit a second mass scale [...] Read more.

Theoretical arguments and lattice simulations suggest that, beside the known resonance of mass

m_{h} =

125 GeV, the Higgs field could exhibit a second mass scale

{(M_{H})}^{theor} = 690 \pm 10 (stat) \pm 20 (sys) GeV

. In spite of its large mass, the heavier state would couple to longitudinal Ws with the same typical strength as the low-mass state at 125 GeV and thus represent a relatively narrow resonance mainly produced at LHC by gluon–gluon fusion. After summarizing these general aspects, we review a recent analysis of LHC data which support the idea of a new resonance in the predicted mass range. Since the correlation among these measurements is very small and since, with a definite theoretical prediction in some mass region, local excesses should not be downgraded by the look-elsewhere effect, we emphasize the present substantial statistical evidence which could become an important discovery by simply adding two, still missing, key analyses of the full RUN2 statistics. Full article

(This article belongs to the Special Issue Higgs and BSM Physics: 10th Anniversary of the Discovery of the Higgs Boson)

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14 pages, 4929 KiB

Open AccessArticle

Cosmic-Ray Acceleration in Supernova Remnants

by Vera G. Sinitsyna and Vera Y. Sinitsyna

Universe 2023, 9(2), 98; https://doi.org/10.3390/universe9020098 - 15 Feb 2023

Cited by 4 | Viewed by 1461

Abstract

Supernova Remnants (SNRs) are generally believed to produce the cosmic rays in our Galaxy due to the powerful supernova blast waves generated by expanding SNRs. In contrast to the leptonic cosmic-ray component that is clearly seen by the SNR emission in a wide [...] Read more.

Supernova Remnants (SNRs) are generally believed to produce the cosmic rays in our Galaxy due to the powerful supernova blast waves generated by expanding SNRs. In contrast to the leptonic cosmic-ray component that is clearly seen by the SNR emission in a wide wavelength range, from radio to high-energy

γ

-ray, the hadronic cosmic-ray component can be detected only by very high energy

γ

-ray emission. Galactic SNRs of various ages have been intensively studied at very high energies. Among them are the shell-type SNRs: Tycho’s SNR, Cas A, IC 443,

γ

Cygni SNR, G166.0+4.3. The results of investigations of listed SNRs obtained in observations at 800 GeV–100 TeV energies by SHALON telescope are presented with spectral energy distribution and emission maps compared with experimental data from the wide energy range, from radio to high-energy gamma-rays. The TeV emission maps of supernova remnants obtained by SHALON are overlaid with ones viewed in radio- frequencies and X-rays to reveal SNR’s essential features which can lead to the effective generation of cosmic rays. The presented experimental data from high and very high energies are considered together with theoretical predictions to test the cosmic ray origin in these objects. Full article

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

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6 pages, 244 KiB

Open AccessCommunication

On the Temperature Dependence of the String-Breaking Distance in QCD

by Dmitry Antonov

Universe 2023, 9(2), 97; https://doi.org/10.3390/universe9020097 - 13 Feb 2023

Cited by 2 | Viewed by 921

Abstract

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can [...] Read more.

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can be falling off either as a Gaussian, as suggested by the Schwinger formula, or as an exponential, which is the case in the London limit of the dual superconductor. We find an excellent agreement of the so-evaluated temperature dependence of the string-breaking distance with the respective lattice data, for the case of the meson-production rate corresponding to the London limit. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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11 pages, 2799 KiB

Open AccessArticle

Automated Classification of Auroral Images with Deep Neural Networks

by Zhiyuan Shang, Zhonghua Yao, Jian Liu, Linli Xu, Yan Xu, Binzheng Zhang, Ruilong Guo and Yong Wei

Universe 2023, 9(2), 96; https://doi.org/10.3390/universe9020096 - 12 Feb 2023

Cited by 4 | Viewed by 1402

Abstract

Terrestrial auroras are highly structured that visualize the perturbations of energetic particles and electromagnetic fields in Earth’s space environments. However, the identification of auroral morphologies is often subjective, which results in confusion in the community. Automated tools are highly valuable in the classification [...] Read more.

Terrestrial auroras are highly structured that visualize the perturbations of energetic particles and electromagnetic fields in Earth’s space environments. However, the identification of auroral morphologies is often subjective, which results in confusion in the community. Automated tools are highly valuable in the classification of auroral structures. Both CNNs (convolutional neural networks) and transformer models based on the self-attention mechanism in deep learning are capable of extracting features from images. In this study, we applied multiple algorithms in the classification of auroral structures and performed a comparison on their performances. Trans-former and ConvNeXt models were firstly used in the analysis of auroras in this study. The results show that the ConvNeXt model can have the highest accuracy of 98.5% among all of the applied algorithms. This study provides a direct comparison of deep learning tools on the application of classifying auroral structures and shows promising capability, clearly demonstrating that auto-mated tools can help to minimize the bias in future auroral studies. Full article

(This article belongs to the Special Issue Auroral Physics)

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11 pages, 1083 KiB

Open AccessArticle

Damping Scenarios of Kink Oscillations of Solar Coronal Loops

by Valery M. Nakariakov and Naga V. Yelagandula

Universe 2023, 9(2), 95; https://doi.org/10.3390/universe9020095 - 11 Feb 2023

Cited by 2 | Viewed by 972

Abstract

The transition from the large-amplitude rapidly-decaying regime of kink oscillations of plasma loops observed in the corona of the Sun to the low-amplitude decayless oscillations is modelled. In this study, the decayless regime is associated with the energy supply from coronal plasma flows, [...] Read more.

The transition from the large-amplitude rapidly-decaying regime of kink oscillations of plasma loops observed in the corona of the Sun to the low-amplitude decayless oscillations is modelled. In this study, the decayless regime is associated with the energy supply from coronal plasma flows, i.e., self-oscillations, or random movements of footpoints of the oscillating loop. The damping is attributed to the linear effect of resonant absorption. We demonstrate that the decay of an impulsively excited kink oscillation to the self-oscillatory stationary amplitude differs from the exponential decay. The damping time is found to depend on the oscillation amplitude to the power of a negative constant whose magnitude is less than unity. In this scenario, a better model for the damping seems to be super-exponential. In the separately considered case of the decayless oscillatory regime supported by a random driver, the oscillation amplitude experiences an exponential decay to the decayless level. Implications of this finding for magnetohydrodynamic seismology of the solar corona based on the effect of resonant absorption are discussed. Full article

(This article belongs to the Special Issue Solar Coronal Loop Dynamics)

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35 pages, 1365 KiB

Open AccessEditor’s ChoiceReview

Hubble Tension: The Evidence of New Physics

by Jian-Ping Hu and Fa-Yin Wang

Universe 2023, 9(2), 94; https://doi.org/10.3390/universe9020094 - 10 Feb 2023

Cited by 56 | Viewed by 3592

Abstract

The

Λ

CDM model provides a good fit to most astronomical observations but harbors large areas of phenomenology and ignorance. With the improvements in the precision and number of observations, discrepancies between key cosmological parameters of this model have emerged. Among them, the [...] Read more.

The

Λ

CDM model provides a good fit to most astronomical observations but harbors large areas of phenomenology and ignorance. With the improvements in the precision and number of observations, discrepancies between key cosmological parameters of this model have emerged. Among them, the most notable tension is the 4

σ

to 6

σ

deviation between the Hubble constant (

H_{0}

) estimations measured by the local distance ladder and the cosmic microwave background (CMB) measurement. In this review, we revisit the

H_{0}

tension based on the latest research and sort out evidence from solutions to this tension that might imply new physics beyond the

Λ

CDM model. The evidence leans more towards modifying the late-time universe. Full article

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

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12 pages, 2434 KiB

Open AccessCommunication

Geminga SNR: Possible Candidate of Local Cosmic-Ray Factory (II)

by Bing Zhao, Yiqing Guo and Xunxiu Zhou

Universe 2023, 9(2), 93; https://doi.org/10.3390/universe9020093 - 09 Feb 2023

Cited by 1 | Viewed by 871

Abstract

Accurate measurements of the energy spectrum and anisotropy can help us discover local cosmic-ray accelerators. Our recent works have shown that spectral hardening above 200 GeV in the energy spectra and transition of large-scale anisotropy at ∼100 TeV are of an unifying origin. [...] Read more.

Accurate measurements of the energy spectrum and anisotropy can help us discover local cosmic-ray accelerators. Our recent works have shown that spectral hardening above 200 GeV in the energy spectra and transition of large-scale anisotropy at ∼100 TeV are of an unifying origin. Less than 100 TeV, both spectral hardening and anisotropy explicitly indicate the dominant contribution from nearby sources. Recent observations of CR anisotropy suggest that this phase is consistent with the locally regular magnetic field (LRMF) of the interstellar boundary explorer (IBEX) below 100 TeV. In this work, we further investigate the parameter space of sources allowed by the observational energy spectra and amplitude and phase of dipole anisotropy. To obtain the best-fit source parameters, a numerical algorithm is to compute the parameter posterior distributions based on Bayesian inference. We found that by combining the observations of the energy spectrum and anisotropy, the parameters of the model can be well constrained. The LRMF and the effect of the corresponding anisotropic diffusion are considered in this work. Finally, the phase results’ right ascension

(R . A .) = 3.2

h below 100 TeV was obtained by fitting, which is in general agreement with the experimental observations. Since the Geminga SNR is very close to the mean of the fitted parameters, it could be a candidate for a local cosmic-ray accelerator. Full article

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

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12 pages, 6808 KiB

Open AccessCommunication

Multi-Periodicity of High-Frequency Type III Bursts as a Signature of the Fragmented Magnetic Reconnection

by Marian Karlický and Ján Rybák

Universe 2023, 9(2), 92; https://doi.org/10.3390/universe9020092 - 09 Feb 2023

Viewed by 891

Abstract

Using the radio spectra of the 2 April 2022 eruptive flare, we analyze a group of highfrequency type III bursts by our new wavelet method. In this analysis, we found a multi-periodicity of these bursts that is interpreted by the electron beams accelerated [...] Read more.

Using the radio spectra of the 2 April 2022 eruptive flare, we analyze a group of highfrequency type III bursts by our new wavelet method. In this analysis, we found a multi-periodicity of these bursts that is interpreted by the electron beams accelerated in the fragmented magnetic reconnection in the rising magnetic rope. We propose that each period in these type III bursts is a result of the periodic interaction of sub-ropes formed in the rising magnetic rope. In each interaction, the period depends on the diameter of interacting sub-ropes and local Alfvén velocity. This interpretation is supported by detection of the specific EUV structure which was, according to our knowledge, observed for the first time. All proposed processes occur in the rising magnetic rope. Thus, this flare deviates from the standard flare model, where the main magnetic reconnection is located below the rising magnetic rope. Full article

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

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8 pages, 292 KiB

Open AccessCommunication

Bandhead Energies of npp/pnn Three-Quasiparticle Quadruplets

by Sushil Kumar, Manpreet Kaur, Sukhjeet Singh, Jagjit Singh and A. K. Jain

Universe 2023, 9(2), 91; https://doi.org/10.3390/universe9020091 - 08 Feb 2023

Viewed by 959

Abstract

Semi-empirical frameworks are widely used in calculating the bandhead energies of three-quasiparticle (3qp) configurations observed in well-deformed odd-A nuclei. In the present study, our aim is to improve the previous version of the semi-empirical model [Physical Review C. 1992, 45(6), 3013]. This is [...] Read more.

Semi-empirical frameworks are widely used in calculating the bandhead energies of three-quasiparticle (3qp) configurations observed in well-deformed odd-A nuclei. In the present study, our aim is to improve the previous version of the semi-empirical model [Physical Review C. 1992, 45(6), 3013]. This is achieved by incorporating the ignored vital contributions owing to the irrotational motion of valance protons/neutrons, diagonal components of particle–particle coupling (ppc), and rotor–particle coupling (rpc) terms. We tested the validity of the improved version of the model by calculating the bandhead energies of twelve 3qp npp/pnn quadruplets observed in ¹⁶³Er, ^171,175,177Lu, ¹⁷⁷Ta, and ¹⁸³Re nuclides. Our new results show better agreement with the experimental data indicating the importance of newly added terms. We strongly expect that the present version of the model will provide support to future experimental campaigns for making configuration assignments to the newly observed 3qp bands and also in the identification of exact Nilsson’s configurations of 3qp quadruplets where experimental data that differentiate among the competing configuration are scarce. Full article

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

17 pages, 763 KiB

Open AccessArticle

Gauge Couplings Evolution from the Standard Model, through Pati–Salam Theory, into E₈ Unification of Families and Forces

by Alfredo Aranda, Francisco J. de Anda, António P. Morais and Roman Pasechnik

Universe 2023, 9(2), 90; https://doi.org/10.3390/universe9020090 - 08 Feb 2023

Cited by 3 | Viewed by 809

Abstract

We explore the potential of ultimate unification of the Standard Model matter and gauge sectors into a single

E_{8}

superfield in ten dimensions via an intermediate Pati–Salam gauge theory. Through a consistent realisation of a [...] Read more.

We explore the potential of ultimate unification of the Standard Model matter and gauge sectors into a single

E_{8}

superfield in ten dimensions via an intermediate Pati–Salam gauge theory. Through a consistent realisation of a

T^{6} / (Z_{6} \times Z_{2} \times Z_{2})

orbifolding procedure and renormalisation group evolution of gauge couplings, we establish several novel benchmark scenarios for New Physics that are worth further phenomenological exploration. Full article

(This article belongs to the Special Issue Higgs and BSM Physics: 10th Anniversary of the Discovery of the Higgs Boson)

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14 pages, 1877 KiB

Open AccessArticle

Polaron Dynamics in a Quasi-Two-Dimensional Bose–Einstein Condensate

by Shukhrat N. Mardonov, Bobir A. Toshmatov, Bobomurat J. Ahmedov and Shukurillo T. Inoyatov

Universe 2023, 9(2), 89; https://doi.org/10.3390/universe9020089 - 08 Feb 2023

Viewed by 1039

Abstract

The concept of polaron quasiparticles was first introduced in the pioneering papers by Landau and Feynman in the 1930s and 1940s. It describes the phenomenon of an external particle producing a bound state in an embedded medium. Since then, the study of polaron [...] Read more.

The concept of polaron quasiparticles was first introduced in the pioneering papers by Landau and Feynman in the 1930s and 1940s. It describes the phenomenon of an external particle producing a bound state in an embedded medium. Since then, the study of polaron quasiparticles has been an active area of research in condensed matter physics, with a wide range of applications in magnetic phenomena and lattice deformation properties. In this paper, we provide a comprehensive review of the polaron quasiparticle phenomenon, including its historical origins, theoretical developments, and current research. We also study the various applications of polaron quasiparticles in condensed matter physics, including in magnetic phenomena and lattice deformation properties. The review concludes with an outlook on future directions of research in this field. In particular, we study the motion of external embedded particles in a quasi-two-dimensional Bose–Einstein condensate confined by the quantum harmonic oscillator. We found that the dynamics of attracting particles with static Bose–Einstein condensate exhibit circular and precessional elliptic trajectories due to centripetal force. Polaron-forming embedded particles in the condensate lead to a strongly nonlinear trajectory of the polaron and dynamics of condensate depending on the initial parameters of the condensate and polaron. Full article

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15 pages, 361 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Gravitational Condensate Stars: An Alternative to Black Holes

by Pawel O. Mazur and Emil Mottola

Universe 2023, 9(2), 88; https://doi.org/10.3390/universe9020088 - 07 Feb 2023

Cited by 50 | Viewed by 2759

Abstract

A new final endpoint of complete gravitational collapse is proposed. By extending the concept of Bose–Einstein condensation to gravitational systems, a static, spherically symmetric solution to Einstein’s equations is obtained, characterized by an interior de Sitter region of

p = - ρ

gravitational [...] Read more.

A new final endpoint of complete gravitational collapse is proposed. By extending the concept of Bose–Einstein condensation to gravitational systems, a static, spherically symmetric solution to Einstein’s equations is obtained, characterized by an interior de Sitter region of

p = - ρ

gravitational vacuum condensate and an exterior Schwarzschild geometry of arbitrary total mass M. These are separated by a phase boundary with a small but finite thickness ℓ, replacing both the Schwarzschild and de Sitter classical horizons. The resulting collapsed cold, compact object has no singularities, no event horizons, and a globally defined Killing time. Its entropy is maximized under small fluctuations and is given by the standard hydrodynamic entropy of the thin shell, which is of order

k_{B} ℓ M c / ℏ

, instead of the Bekenstein–Hawking entropy,

S_{B H} = 4 π k_{B} G M^{2} / ℏ c

. Unlike BHs, a collapsed star of this kind is consistent with quantum theory, thermodynamically stable, and suffers from no information paradox. Full article

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

23 pages, 1369 KiB

Open AccessArticle

Applications of Thermodynamic Geometries to Conformal Regular Black Holes: A Comparative Study

by Abdul Jawad, Mazhar Hussain and Shamaila Rani

Universe 2023, 9(2), 87; https://doi.org/10.3390/universe9020087 - 07 Feb 2023

Cited by 2 | Viewed by 1153

Abstract

In this paper, we investigate the thermal stability and thermodynamic geometries of non-rotating/rotating charged black holes. For these black holes, we apply barrow entropy to determine the physical quantities such as mass and temperature of the system and find their stability through first [...] Read more.

In this paper, we investigate the thermal stability and thermodynamic geometries of non-rotating/rotating charged black holes. For these black holes, we apply barrow entropy to determine the physical quantities such as mass and temperature of the system and find their stability through first and second phase transitions of the heat capacity. We analyze the effects of scalar charge Q and hair parameter

λ

on black holes properties by taking both positive and negative values of these parameters. It is noted that heat capacity provide the stable, unstable regions and phase transition points for both black holes. To investigate the thermodynamic geometry of these black holes, various techniques such as Ruppeiner, Weinhold, Quevedo, and HPEM metrics are considered. It is observed that Weinhold, Quevedo, and HPEM give attractive/repulsive behavior of particles in stable/unstable regions of black holes. Full article

(This article belongs to the Section Compact Objects)

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18 pages, 3813 KiB

Open AccessArticle

Temperature Variations in the Mesosphere and Lower Thermosphere during Geomagnetic Storms with Disparate Durations at High Latitudes

by Guanchun Wei, Jianyong Lu, Wenbin Wang, Yufeng Tian, Jingyuan Li, Shiping Xiong, Meng Sun, Fuzhen Shen, Zheng Li, Hua Zhang, Jingqi Cui, Chaolei Yang, Jingrui Yao, Shuwen Jiang, Zhixin Zhu and Jingye Wang

Universe 2023, 9(2), 86; https://doi.org/10.3390/universe9020086 - 05 Feb 2023

Viewed by 1072

Abstract

Using the temperature data observed from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), we investigate the response of the mesosphere and lower thermosphere (MLT) to two medium geomagnetic storms with disparate durations, on 20 April 2018 and 10 April 2022. [...] Read more.

Using the temperature data observed from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), we investigate the response of the mesosphere and lower thermosphere (MLT) to two medium geomagnetic storms with disparate durations, on 20 April 2018 and 10 April 2022. The high-latitude MLT temperature increase in the Southern hemisphere can reach 40 K during April 2018 geomagnetic storm with a longer duration (Kp values greater than 4 for 15 h), while the temperature variations are less than 10 K for the April 2022 event (Kp values greater than 4 for 6 h). To investigate the different temperature responses to disparate geomagnetic storm durations and understand what physical process results in this difference, we simulated the two events using the thermosphere ionosphere mesosphere electrodynamics general circulation model (TIMEGCM). The simulations show that more particles and energy input in longer-duration geomagnetic storms produce larger ion drag force and pressure gradient force at ~130 km, and then the enhanced two forces cause faster horizontal wind, leading to larger horizontal divergence. Subsequently, the stronger downward vertical wind is transported to the MLT region (below 110 km) and ultimately makes greater temperature increases through adiabatic heating/cooling and vertical advection. Therefore, the effects of the storm’s duration on the MLT temperature are also important. Full article

(This article belongs to the Special Issue Auroral Physics)

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14 pages, 320 KiB

Open AccessArticle

On the Appearance of Time in the Classical Limit of Quantum Gravity

by Roger I. Ayala Oña, Darya P. Kislyakova and Tatyana P. Shestakova

Universe 2023, 9(2), 85; https://doi.org/10.3390/universe9020085 - 05 Feb 2023

Cited by 1 | Viewed by 1994

Abstract

A possible solution of the problem of time in the Wheeler–DeWitt quantum geometrodynamics is that time appears within a semiclassical limit. Following this line of thinking, one can come to the Schrodinger equation for matter fields in curved spacetime with quantum-gravitational corrections. In [...] Read more.

A possible solution of the problem of time in the Wheeler–DeWitt quantum geometrodynamics is that time appears within a semiclassical limit. Following this line of thinking, one can come to the Schrodinger equation for matter fields in curved spacetime with quantum-gravitational corrections. In the present paper, we study the semiclassical limit in the case of a closed isotropic model with a scalar field decomposed into modes. We analyse calculations made within frameworks of three approaches. The first approach was proposed by Kiefer and Singh. Since the Wheeler–DeWitt equation does not contain a time derivative, it is constructed by means of a special mathematical procedure, a time variable being a parameter along a classical trajectory of gravitational field. The second method was suggested in the paper of Maniccia and Montani, who introduced the Kuchař–Torre reference fluid as an origin of time. Furthermore, the third is the extended phase space approach to the quantisation of gravity. In this approach, the temporal Schrodinger equation is argued to be more fundamental than the Wheeler–DeWitt equation, and there is no problem of time. Time is introduced due to fixing a reference frame of a certain observer, who can register the macroscopic consequences of quantum gravitational phenomena in the Very Early Universe. To go to the semiclassical limit, the Born–Oppenheimer approximation for gravity is used. In each of the approaches, in the order of

O (1 / M)

, a temporal Schrödinger equation for matter fields in curved spacetime with quantum gravitational corrections is obtained. However, equations and corrections are different in various approaches, and the results depend on the additional assumptions made within the scopes of these approaches. Full article

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

14 pages, 1184 KiB

Open AccessArticle

Self-Enrichment in Globular Clusters: The Crucial Role Played by Oxygen

by Erendira Huerta-Martinez, Claudio Gavetti and Paolo Ventura

Universe 2023, 9(2), 84; https://doi.org/10.3390/universe9020084 - 04 Feb 2023

Viewed by 955

Abstract

Results from photometry and high-resolution spectroscopy have demonstrated the existence of multiple populations in globular clusters, where one or more stellar generations of stars coexist with the original population. We study the possibility that the new generation(s) of stars formed from the gas [...] Read more.

Results from photometry and high-resolution spectroscopy have demonstrated the existence of multiple populations in globular clusters, where one or more stellar generations of stars coexist with the original population. We study the possibility that the new generation(s) of stars formed from the gas lost by intermediate mass (4–8

M_{⊙}

) stars during the asymptotic giant branch (AGB) evolution, possibly after dilution with residual pristine gas in the cluster. To this aim, we confront the chemistry of the AGB ejecta with the distribution of the chemical composition of stars in NGC 6402. We find that a satisfactory consistency between the observational evidence and the self-enrichment by AGBs hypothesis is reached if the mass-loss rates experienced for the latter stars is ∼10 times smaller than found for the solar metallicity counterparts of the same mass. We also comment on the importance of the knowledge of the oxygen abundance as a key indicator of the extent of the nucleosynthesis at which the gas from which the stars belonging to the second generation of the clusters formed, and the degree of dilution with pristine gas. Full article

(This article belongs to the Section Stellar Astronomy)

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20 pages, 903 KiB

Open AccessArticle

Generic Modification of Gravity, Late Time Acceleration and Hubble Tension

by Mayukh R. Gangopadhyay, Shibesh K. Jas Pacif, Mohammad Sami and Mohit K. Sharma

Universe 2023, 9(2), 83; https://doi.org/10.3390/universe9020083 - 03 Feb 2023

Cited by 8 | Viewed by 1382

Abstract

We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom, but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the standard conservation, and evolution has the [...] Read more.

We consider a scenario of large-scale modification of gravity that does not invoke extra degrees of freedom, but includes coupling between baryonic matter and dark matter in the Einstein frame. The total matter energy density follows the standard conservation, and evolution has the character of deceleration in this frame. The model exhibits interesting features in the Jordan frame realised by virtue of a disformal transformation where individual matter components adhere to standard conservation but gravity is modified. A generic parametrization of disformal transformation leaves thermal history intact and gives rise to late time acceleration in the Jordan frame, which necessarily includes phantom crossing, which, in the standard framework, can be realised using at least two scalar fields. This scenario is embodied by two distinguished features, namely, acceleration in the Jordan frame and deceleration in the Einstein frame, and the possibility of resolution of the Hubble tension thanks to the emergence of the phantom phase at late times. Full article

(This article belongs to the Special Issue Modified Gravity Approaches to the Tensions of ΛCDM)

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11 pages, 340 KiB

Open AccessArticle

Some Aspects of Persistent Homology Analysis on Phase Transition: Examples in an Effective QCD Model with Heavy Quarks

by Hayato Antoku and Kouji Kashiwa

Universe 2023, 9(2), 82; https://doi.org/10.3390/universe9020082 - 03 Feb 2023

Cited by 2 | Viewed by 978

Abstract

Recently, persistent homology analysis has been used to investigate phase structure. In this study, we apply persistent homology analysis to the QCD effective model with heavy quarks at finite imaginary chemical potential; i.e., the Potts model with the suitably tuned external field. Since [...] Read more.

Recently, persistent homology analysis has been used to investigate phase structure. In this study, we apply persistent homology analysis to the QCD effective model with heavy quarks at finite imaginary chemical potential; i.e., the Potts model with the suitably tuned external field. Since we try to obtain a deeper understanding of the relationship between persistent homology and phase transition in QCD, we consider the imaginary chemical potential because the clear phase transition, which is closely related to the confinement-deconfinement transition, exists. In the actual analysis, we employ the point-cloud approach to consider persistent homology. In addition, we investigate the fluctuation of persistent diagrams to obtain additional information on the relationship between the spatial topology and the phase transition. Full article

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

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