Universe

31 pages, 2176 KB

Open AccessArticle

Models of Charged Gravastars in f(T)-Gravity

by Mohamed A. Bakry and Ali Eid

Universe 2025, 11(10), 353; https://doi.org/10.3390/universe11100353 - 21 Oct 2025

Viewed by 209

This study investigates three distinct charged gravastar models within the framework of

f (T)

modified gravity, considering the functional forms

f (T) = T

,

f (T) = a + b T

, and

f (T) = T^{2}

. Inspired by the [...] Read more.

This study investigates three distinct charged gravastar models within the framework of

f (T)

modified gravity, considering the functional forms

f (T) = T

,

f (T) = a + b T

, and

f (T) = T^{2}

. Inspired by the Mazur–Mottola conjecture, we propose these models as singularity-free alternatives to black holes, each characterized by a three-region structure: (i) an interior de Sitter core, (ii) an intermediate thin shell composed of ultrarelativistic matter, and (iii) an exterior region described by the Reisner Nordstrom solution and other novel spherically symmetric vacuum solutions. We derive a complete set of exact, singularity-free solutions for the charged gravastar configuration, demonstrating their mathematical consistency and physical viability in the context of alternative gravity theories. Notably, the field equations governing the thin shell are solved using an innovative approach based on Killing vector symmetries, eliminating the need for approximations commonly employed in prior studies. Furthermore, we analyze key physical properties of the thin shell, including its proper length, entropy distribution, and energy content. A thorough examination of the energy conditions reveals the thermodynamic stability and viability of these models. Our results contribute to the growing body of work on exotic compact objects and provide new insights into the interplay between modified gravity, electromagnetism, and non-singular black hole alternatives. Full article

(This article belongs to the Section Gravitation)

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18 pages, 3404 KB

Open AccessArticle

Model-Independent Inference of Galaxy Star Formation Histories in the Local Volume

by Robin Eappen and Pavel Kroupa

Universe 2025, 11(10), 352; https://doi.org/10.3390/universe11100352 - 20 Oct 2025

Viewed by 221

Abstract

Understanding the diversity of star formation histories (SFHs) of galaxies is key to reconstructing their evolutionary paths. Traditional models often assume parametric forms such as delayed-

τ

or exponentially declining models, which may not reflect the actual variety of formation processes. We aim [...] Read more.

Understanding the diversity of star formation histories (SFHs) of galaxies is key to reconstructing their evolutionary paths. Traditional models often assume parametric forms such as delayed-

τ

or exponentially declining models, which may not reflect the actual variety of formation processes. We aim to assess what types of SFHs are consistent with the observed present-day star formation rates (

{SFR}_{0}

) and time-averaged star formation rates (

⟨ SFR ⟩

) of galaxies in the Local Volume, without assuming any fixed functional form. We construct a non-parametric framework by generating large ensembles of randomized SFHs for each galaxy in the sample. For each SFH, we compute its predicted stellar mass and present-day SFR and retain only those consistent with the observed values within a 20% tolerance. We then infer the statistical distribution of power-law slopes

η

(fitted as

SFR (t) \propto {(t - t_{start})}^{η}

) and 50% stellar mass formation times

t_{50}

. Across the full sample of 555 galaxies, we find that ≈70% have flat SFHs (

| η | \leq 0.01

), ≈24% are mildly declining (

η < - 0.01

), and ≈6% are rising (

η > 0.01

). In the low-mass bin (

M_{★} < 3 \times 10^{9} M_{⊙}

), rising SFHs slightly increase (≈7%) but remain a minority as the majority have flat SFHs. Both

η

and

t_{50}

correlate strongly with the SFR ratio (Spearman

ρ > 0.75

,

p ≪ 10^{- 16}

), indicating that the shape and timing of star formation are primarily governed by this ratio. The

t_{50}

distribution shows sharp spikes near 7.74 and 7.86 Gyr, which we attribute to grid discretization combined with filtering, rather than a physical bimodality. Our results confirm that strongly declining SFH templates are disfavored in the Local Volume: most systems are consistent with flat long-term SFHs, with only mild decline or occasional rising. Importantly, this is demonstrated through a fully model-independent, data-driven approach, with per-galaxy uncertainties quantified using the standard error of

η

and

t_{50}

from the ensemble of accepted SFHs. Full article

(This article belongs to the Section Galaxies and Clusters)

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24 pages, 679 KB

Open AccessArticle

Study of Singly Charmed Dibaryons in Quark Model

by Yuxuan Du, Yao Cui, Zhiyun Tan, Jin Tao, Hongxia Huang and Jialun Ping

Universe 2025, 11(10), 351; https://doi.org/10.3390/universe11100351 - 20 Oct 2025

Viewed by 202

Abstract

We perform a systematic investigation of low-lying singly charmed dibaryon systems with

J = 1

,

I = 0, \frac{1}{2}, 1, \frac{3}{2}, 2, \frac{5}{2}

and strangeness [...] Read more.

We perform a systematic investigation of low-lying singly charmed dibaryon systems with

J = 1

,

I = 0, \frac{1}{2}, 1, \frac{3}{2}, 2, \frac{5}{2}

and strangeness

S = - 1, - 2, - 3, - 4, - 5

in the chiral quark model. According to the analysis of effective potentials, dibaryon systems characterized by lower isospin and magnitude of strangeness exhibit stronger attractive interactions, which may enhance their tendency to form bound states. Experimental efforts may therefore prioritize the search for such configurations. The bound-state calculation results indicate that we have obtained some single-channel bound states, which are

Σ Σ_{c}

,

Σ Σ_{c}^{*}

,

Σ^{*} Σ_{c}

,

Σ^{*} Σ_{c}^{*}

with

I = 0, S = - 1

;

Σ_{c} Δ

,

Σ_{c}^{*} Δ

with

I = \frac{1}{2}, S = 0

;

Σ Σ_{c}

with

I = 1, S = - 1

;

Σ_{c} Δ

with

I = \frac{3}{2}, S = 0

; and

Ξ^{*} Σ_{c}^{*}

with

I = \frac{3}{2}, S = - 2

. However, these states can decay through open channels. We have listed both these single-channel bound states and their corresponding decay channels in this work for experimental reference and search. In the future, we need to study the scattering processes of the open channels further to confirm whether these states are resonance states. Full article

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

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26 pages, 406 KB

Open AccessArticle

A Quasigroup Approach for Conservation Laws in Asymptotically Flat Spacetimes

by Alfonso Zack Robles, Alexander I. Nesterov and Claudia Moreno

Universe 2025, 11(10), 350; https://doi.org/10.3390/universe11100350 - 20 Oct 2025

Viewed by 370

Abstract

In the framework of the quasigroup approach to conservation laws in general relativity, we show how the infinite-parametric Newman–Unti group of asymptotic symmetries can be reduced to the Poincaré quasigroup. We compute Noether’s charges associated with any element of the Poincaré quasialgebra. The [...] Read more.

In the framework of the quasigroup approach to conservation laws in general relativity, we show how the infinite-parametric Newman–Unti group of asymptotic symmetries can be reduced to the Poincaré quasigroup. We compute Noether’s charges associated with any element of the Poincaré quasialgebra. The integral conserved quantities of energy momentum and angular momentum, being linear on generators of the Poincaré quasigroup, are identically equal to zero in Minkowski spacetime. We present a definition of the angular momentum free of the supertranslation ambiguity. We provide an appropriate notion of intrinsic angular momentum and a description of the mass reference frame’s center at future null infinity. Finally, in the center of mass reference frame, the momentum and angular momentum are defined by the Komar expression. Full article

(This article belongs to the Special Issue The 10th Anniversary of Universe: Standard Cosmological Models, and Modified Gravity and Cosmological Tensions)

13 pages, 1519 KB

Open AccessArticle

Thermodynamic Assessment of Prebiotic Molecule Formation Pathways on Comets

by Luca Tonietti

Universe 2025, 11(10), 349; https://doi.org/10.3390/universe11100349 - 18 Oct 2025

Viewed by 232

Abstract

Comets are chemically rich and thermally extreme, spanning surface temperatures from ~50 K in the Oort Cloud to >1000 K for sungrazing bodies. These conditions may support key steps of prebiotic chemistry, including the synthesis of nucleic acid precursors. This study present a [...] Read more.

Comets are chemically rich and thermally extreme, spanning surface temperatures from ~50 K in the Oort Cloud to >1000 K for sungrazing bodies. These conditions may support key steps of prebiotic chemistry, including the synthesis of nucleic acid precursors. This study present a thermodynamic evaluation of seven candidate reactions, producing nitrogenous bases, sugars, nucleosides, and nucleotides, across the cometary temperature spectrum, 50–1000 K. Purine nucleobase synthesis, including adenine formation via aminoacetonitrile polymerization and HCN polymerization, is strongly exergonic at all temperatures. Sugar formation from formaldehyde is also exergonic, while intermediate pathways, e.g., 2-aminooxazole synthesis, become thermodynamically viable only above ~700 K. Nucleoside formation is thermodynamically neutral at low T but becomes favorable at elevated temperatures, whereas phosphorylation to AMP, i.e., adenosine-monophosphate, a nucleotide serving as a critical regulator of cellular energy status, remains highly endergonic under the entire T range studied. My analysis suggests that, under standard-state assumptions, comets can thermodynamically support formation routes of nitrogenous bases and simple sugars but not a complete nucleotide assembly. This supports a dual-phase origin scenario, where comets act as molecular reservoirs, with further polymerization and biological activation occurring post-delivery on planetary surfaces. Importantly, these findings represent purely thermodynamic assessments under standard-state assumptions and do not address kinetic barriers, catalytic influences, or adsorption effects on ice or mineral surfaces. The results should therefore be viewed as a baseline map of feasibility, subject to modifications in more complex chemical environments. Full article

(This article belongs to the Section Planetary Sciences)

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31 pages, 5922 KB

Open AccessArticle

The Iwasawa–Taniguchi Effect in Compton-thick Seyfert 2 Galaxies with Extended Hard X-Ray Emission

by Jia Chen, Huili Yi, Chengchao Liu, Shenfang Ye and Shuangxi Yi

Universe 2025, 11(10), 348; https://doi.org/10.3390/universe11100348 - 18 Oct 2025

Viewed by 201

Abstract

The anti-correlation between the equivalent width of the neutral narrow Fe K

α

line and the 2–10 keV luminosity (the Iwasawa–Taniguchi effect) in the nuclear regions of active galactic nuclei has been debated in recent years. With the high angular resolution of Chandra, [...] Read more.

The anti-correlation between the equivalent width of the neutral narrow Fe K

α

line and the 2–10 keV luminosity (the Iwasawa–Taniguchi effect) in the nuclear regions of active galactic nuclei has been debated in recent years. With the high angular resolution of Chandra, an increasing number of Compton-thick sources have been found to show extended narrow Fe K

α

emission on scales from tens of parsecs to kiloparsecs, attributed to reprocessing of nuclear radiation by surrounding Compton-thick material. We analyze eight Compton-thick sources with prominent extended Fe K

α

emission. We confirm the Iwasawa–Taniguchi effect in the extended component relative to the reflection spectrum, with a steeper slope, indicating reduced production efficiency of neutral Fe K

α

photon outside the nucleus. Both the reflection spectrum and Fe K

α

luminosities correlate positively with intrinsic AGN luminosity, suggesting that the nucleus drives the extended emission. Finally, we find a linear relationship between redshift and the equivalent width of the nuclear Fe K

α

line, with no such trend in the extended component. Full article

(This article belongs to the Special Issue 10th Anniversary of Universe: Galaxies and Their Black Holes)

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10 pages, 330 KB

Open AccessArticle

Traversable Kaluza–Klein Wormholes?

by Christopher Simmonds and Matt Visser

Universe 2025, 11(10), 347; https://doi.org/10.3390/universe11100347 - 17 Oct 2025

Viewed by 293

Abstract

Various authors have suggested that Kaluza–Klein variants of traversable wormholes might to some extent ameliorate the defocussing properties (the curvature condition violations, and implied energy condition violations) inherent in positing the existence of a traversable wormhole throat. Unfortunately such a hope is ill-founded. [...] Read more.

Various authors have suggested that Kaluza–Klein variants of traversable wormholes might to some extent ameliorate the defocussing properties (the curvature condition violations, and implied energy condition violations) inherent in positing the existence of a traversable wormhole throat. Unfortunately such a hope is ill-founded. We shall show that in a traditional Kaluza–Klein context the price paid for completely eliminating the defocussing properties of the wormhole throat is extremely high—to completely eliminate curvature condition violations the 5th dimension has to become truly enormous (formally infinite) in the vicinity of the wormhole throat, in a manner that is fundamentally incompatible with the traditional Kaluza–Klein ansatz. At best, the extra dimensions allow one to move the curvature condition violations around, they cannot be eliminated except at prohibitive cost. While traversable Kaluza–Klein wormholes might be interesting for other reasons, it must be emphasized that adding a 5th dimension is not particularly useful in terms of ameliorating violations of the curvature conditions. Full article

(This article belongs to the Special Issue Celebrating the 110th Anniversary of General Relativity: Advances, Challenges and Perspectives)

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21 pages, 454 KB

Open AccessArticle

Cosmology at the End of Time

by Meir Shimon

Universe 2025, 11(10), 346; https://doi.org/10.3390/universe11100346 - 16 Oct 2025

Viewed by 328

Abstract

If the recent acceleration phase of the expanding Universe is driven by a cosmologicalconstant the Universe is future-eternal with a few far reaching ramifications and disturbing consequences. We demonstrate with a non-ΛCDM cosmological model, that is nearly identical to the standard cosmological model [...] Read more.

If the recent acceleration phase of the expanding Universe is driven by a cosmologicalconstant the Universe is future-eternal with a few far reaching ramifications and disturbing consequences. We demonstrate with a non-ΛCDM cosmological model, that is nearly identical to the standard cosmological model insofar observations of our past are concerned—but otherwise has an effective cosmic time cutoff—that under certain plausible assumptions observers will virtually always find themselves at or near the end of time (EOT) terminal point, where H₀η₀ = π, and H₀ and η₀ are the present day expansion rate and the conformal time, respectively. Assuming a locally flat ΛCDM model for concreteness (but with a global terminal point which is with an overwhelming probability the present time) such observers will invariably infer that the energy densities associated with the cosmological constant, Λ, and non-relativistic (NR) matter constitute 67.5% and 32.5%, respectively, of the cosmic energy budget at present, which lie well within the 2σ confidence level of the concordance 68.5% and 31.5% values. This addresses the Cosmic Coincidence Problem associated with Λ. Future high-precision cosmological probes will be able to break the observational degeneracy between the proposed model and flat ΛCDM. A few additional implications of the proposed model are discussed as well. Full article

(This article belongs to the Section Cosmology)

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18 pages, 905 KB

Open AccessArticle

Chiral Invariant Mass Constraints from HESS J1731–347 in an Extended Parity Doublet Model with Isovector Scalar Meson

by Yuk Kei Kong, Bikai Gao and Masayasu Harada

Universe 2025, 11(10), 345; https://doi.org/10.3390/universe11100345 - 16 Oct 2025

Viewed by 322

Abstract

The recent discovery of an extremely light and small central compact object (CCO) within the supernova remnant HESS J1731-347, with mass

0 . 77_{- 0.17}^{+ 0.20} M_{⊙}

and radius

10 . 4_{- 0.78}^{+ 0.86}

km, is challenging our [...] Read more.

The recent discovery of an extremely light and small central compact object (CCO) within the supernova remnant HESS J1731-347, with mass

0 . 77_{- 0.17}^{+ 0.20} M_{⊙}

and radius

10 . 4_{- 0.78}^{+ 0.86}

km, is challenging our understanding of neutron stars. In this article, we identify it as an ultra-light neutron star (NS) and constrain the chiral invariant mass of nucleon

m_{0}

from the observational data of NS using an extended parity doublet model with the isovector scalar meson

a_{0} (980)

. We show that the

1 σ

data from the HESS J1731-347 impose a very narrow constraint on the allowed values of

m_{0}

and

L_{0}

in the crossover model:

830 MeV ≲ m_{0} ≲ 900 MeV

for

L_{0} = 40

MeV, and

850 MeV ≲ m_{0} ≲ 890 MeV

for

L_{0} = 45

MeV. We also study the higher-order asymmertic matter properties such as the symmetry incompressibility

K_{s y m}

and the symmetry skewness

Q_{s y m}

in the presence of the

a_{0}

meson. We find that

K_{s y m}

and

Q_{s y m}

are very sensitive to

m_{0}

in the presence of the

a_{0}

meson. Full article

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram 2024)

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19 pages, 809 KB

Open AccessArticle

The Mass Profile of NGC 3268 from Its Stellar Kinematics

by Juan Pablo Caso, Bruno Javier De Bórtoli and Tom Richtler

Universe 2025, 11(10), 344; https://doi.org/10.3390/universe11100344 - 16 Oct 2025

Viewed by 183

Abstract

The mass profile of the central galaxy of the Antlia cluster, NGC 3268, is studied through a spherical Jeans analysis, combined with a Bayesian approach. The prior distributions are derived from dark matter simulations. The observational dataset consists of Gemini/GMOS multi-object spectra observed [...] Read more.

The mass profile of the central galaxy of the Antlia cluster, NGC 3268, is studied through a spherical Jeans analysis, combined with a Bayesian approach. The prior distributions are derived from dark matter simulations. The observational dataset consists of Gemini/GMOS multi-object spectra observed from several programmes, supplemented with the kinematics of a small sample of globular clusters from the literature. An NFW mass profile and several options of constant anisotropy are considered. The analysis indicates a moderately massive halo, with a virial mass of (1.4 – 4.3)

\times 10^{13} M_{⊙}

, depending on the assumed anisotropy. A comparison with the kinematics of the galaxy population from the Antlia cluster suggests that a fraction of galaxies is not yet virialised and may currently be infalling into the cluster. Full article

(This article belongs to the Section Galaxies and Clusters)

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17 pages, 6775 KB

Open AccessArticle

Gravitational Wave Signatures of Warm Dark Matter in the Gauge Extensions of the Standard Model

by Lucia A. Popa

Universe 2025, 11(10), 343; https://doi.org/10.3390/universe11100343 - 15 Oct 2025

Viewed by 156

Abstract

We studied the left-right symmetric extension of the standard model (LRSM), featuring a TeV-scale, right-handed (RH) gauge boson

W_{R}

and three RH neutrinos. This setup naturally realizes the type-II seesaw mechanism for active neutrino masses. We identified the conditions that yield sufficient [...] Read more.

We studied the left-right symmetric extension of the standard model (LRSM), featuring a TeV-scale, right-handed (RH) gauge boson

W_{R}

and three RH neutrinos. This setup naturally realizes the type-II seesaw mechanism for active neutrino masses. We identified the conditions that yield sufficient entropy dilution to reconcile the keV sterile neutrino dark matter energy density with observations while inducing an early matter domination (EMD) phase. These constrained the lightest active neutrino mass to

8.59 \times 10^{- 10} eV < m_{ν_{1}} < 5.06 \times 10^{- 9} eV

. The resulting frequency-dependent suppression of the stochastic gravitational wave (GW) background was set by the mass and lifetime of the heavier RH neutrinos. Computing the signal-to-noise ratio (SNR) for future detectors, we found that a blue-tilted primordial tensor spectrum can boost the GW signal to detectable levels (SNR > 10) in experiments such as LISA, BBO, and DECIGO. Full article

(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy, 2nd Edition)

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14 pages, 3243 KB

Open AccessArticle

The 1 June 2025 Forbush Decrease Measured over a Range of Primary Cosmic Ray Energies

by Roger Clay

Universe 2025, 11(10), 342; https://doi.org/10.3390/universe11100342 - 15 Oct 2025

Viewed by 302

Abstract

The 1 June 2025 Forbush decrease in the terrestrial ground-level flux of cosmic ray secondaries was recorded by many cosmic ray systems. This was the deepest such decrease from the quiescent value of the flux, which has been observed over the past two [...] Read more.

The 1 June 2025 Forbush decrease in the terrestrial ground-level flux of cosmic ray secondaries was recorded by many cosmic ray systems. This was the deepest such decrease from the quiescent value of the flux, which has been observed over the past two decades. It resulted from a complex series of solar events, none of which on its own reached the most extreme level. The extreme depth of this decrease has enabled measurements of the flux reduction to be made, which would normally be severely limited by particle counting statistics. In particular, here we examine the decrease phenomenon over a primary cosmic ray energy range, which is rarely accessible due to the low flux of high energy cosmic rays. This work considers data mainly from a muon telescope system, which can respond to both unaccompanied muons and small cosmic ray air showers, providing data from GeV to mid-TeV energies, where the Forbush decrease ceases to be statistically observable. This paper examines the depth of the flux decrease, as a fraction below its quiescent value, over that primary energy range. The progressive development of internal time structure in the flux through the seven days of the phenomenon is also demonstrated. Full article

(This article belongs to the Section Space Science)

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12 pages, 544 KB

Open AccessArticle

Ringing of Reissner–Nordström Black Holes with a Non-Abelian Hair in Gravity’s Rainbow

by Mehrab Momennia

Universe 2025, 11(10), 341; https://doi.org/10.3390/universe11100341 - 15 Oct 2025

Viewed by 235

Abstract

In this paper, we consider massless scalar perturbations minimally coupled to gravity in the background spacetime of charged black holes in Yang–Mills theory with gravity’s rainbow modification. We calculate the corresponding quasinormal frequencies by employing the sixth-order Wentzel—Kramers—Brillouin (WKB) approximation for both asymptotically [...] Read more.

In this paper, we consider massless scalar perturbations minimally coupled to gravity in the background spacetime of charged black holes in Yang–Mills theory with gravity’s rainbow modification. We calculate the corresponding quasinormal frequencies by employing the sixth-order Wentzel—Kramers—Brillouin (WKB) approximation for both asymptotically flat and de Sitter (dS) spacetimes. We show that the Yang–Mills modification of the Reissner–Nordström black holes leads to an increase in the real and imaginary parts of frequencies. Furthermore, we find that the perturbations in asymptotically flat spacetime decay faster with more oscillations compared to dS spacetime, and we study the effects of the rainbow functions on the oscillations. Interestingly, we reveal a novel feature of this black hole case study and show that, unlike typical black hole solutions such as Schwarzschild, RN, and Kerr, the higher multipole numbers live longer than the lower ones in both asymptotically flat and dS spacetimes. Furthermore, the reflection and transmission coefficients are explored for Einstein–Maxwell–Yang–Mills black holes, and the results are compared for flat and dS asymptotes. Full article

(This article belongs to the Special Issue Celebrating the 110th Anniversary of General Relativity: Advances, Challenges and Perspectives)

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23 pages, 11431 KB

Open AccessArticle

Characterisation of Nearby Ultracool Dwarf Candidates with OSIRIS/GTC: First Detection of Balmer Line Emission from the Dwarf Carbon Star LSR J2105+2514

by Antoaneta Antonova, Peter Pessev, Valeri Golev and Dinko Dimitrov

Universe 2025, 11(10), 340; https://doi.org/10.3390/universe11100340 - 14 Oct 2025

Viewed by 204

Abstract

Based on low-resolution OSIRIS/GTC optical spectra, we assign spectral classes to 38 poorly studied ultracool/brown dwarf candidates from the 2MASS database. For almost all of the targets, this is the first optical spectral classification. For the dwarfs showing H

α

emission, we calculate [...] Read more.

Based on low-resolution OSIRIS/GTC optical spectra, we assign spectral classes to 38 poorly studied ultracool/brown dwarf candidates from the 2MASS database. For almost all of the targets, this is the first optical spectral classification. For the dwarfs showing H

α

emission, we calculate the ratio of H

α

to bolometric luminosity, which is the most common characteristic of magnetic activity in cool stars. For the others, we give 3

σ

upper limits. We also include estimates of the effective temperatures and log g and distances from Gaia based on a comparison with models. For one of our targets—LSR J2105+2514, previously classified as a dwarf carbon star—we confirm this classification and report H

α

and H

β

line emission in the spectrum for the first time. Dwarf carbon stars (dC) are low-mass main sequence stars that have undergone mass-transfer binary evolution. The Balmer line emission from these objects most likely indicates coronal activity of the dwarf, which in turn may be due to either intrinsic magnetic activity or spin-up from accretion or tidal locking. Full article

(This article belongs to the Special Issue Magnetic Fields and Activity in Stars: Origins and Evolution)

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15 pages, 296 KB

Open AccessArticle

Symplectic Realization of Generalized Snyder–Poisson Algebra

by V. G. Kupriyanov and E. L. F. de Lima

Universe 2025, 11(10), 339; https://doi.org/10.3390/universe11100339 - 14 Oct 2025

Viewed by 173

Abstract

We investigate Snyder spacetime and its generalizations, including Yang and Snyder–de Sitter spaces, which constitute manifestly Lorentz-invariant noncommutative geometries. This work initiates a systematic study of gauge theory on such spaces in the semi-classical regime, formulated as Poisson gauge theory. As a first [...] Read more.

We investigate Snyder spacetime and its generalizations, including Yang and Snyder–de Sitter spaces, which constitute manifestly Lorentz-invariant noncommutative geometries. This work initiates a systematic study of gauge theory on such spaces in the semi-classical regime, formulated as Poisson gauge theory. As a first step, we construct the symplectic realizations of the relevant noncommutative spaces, a prerequisite for defining Poisson gauge transformations and field strengths. We present a general method for representing the Snyder algebra and its extensions in terms of canonical phase-space variables, enabling both the reproduction of known representations and the derivation of novel ones. These canonical constructions are employed to obtain explicit symplectic realizations for the Snyder–de Sitter space and to construct the deformed partial derivative which differentiates the underlying Poisson structure. Furthermore, we analyze the motion of freely falling particles in these backgrounds and comment on the geometry of the associated spaces. Full article

(This article belongs to the Section Field Theory)

25 pages, 812 KB

Open AccessArticle

Constructing Regular Lovelock Black Holes with Degenerate Vacuum and Λ < 0 Using the Gravitational Tension—Shadow Analysis

by Reginaldo Prado-Fuentes, Rodrigo Aros, Milko Estrada and Bastian Astudillo

Universe 2025, 11(10), 338; https://doi.org/10.3390/universe11100338 - 13 Oct 2025

Viewed by 318

Abstract

Recently, a link between gravitational tension (GT) and energy density via the Kretschmann scalar (KS) was proposed to construct regular black holes (RBHs) in pure Lovelock (PL) gravity. However, including a negative cosmological constant in PL gravity leads to a curvature singularity. Here, [...] Read more.

Recently, a link between gravitational tension (GT) and energy density via the Kretschmann scalar (KS) was proposed to construct regular black holes (RBHs) in pure Lovelock (PL) gravity. However, including a negative cosmological constant in PL gravity leads to a curvature singularity. Here, we choose the coupling constants such that the Lovelock equations admit an n-fold degenerate AdS vacuum (LnFDGS), allowing us to construct an RBH with

Λ < 0

, where the energy density is analogous to the previously mentioned model. To achieve this, we propose alternative definitions for both the KS and GT. We find that, for mass parameter values greater than the extremal value

M_{\min}

, our RBH solution becomes indistinguishable from the AdS vacuum black hole from inside the event horizon out to infinity. At small scales, quantum effects modify the geometry and thermodynamics, removing the singularity. Furthermore, due to the lack of analytical relationships between the event horizon, photon sphere, and shadow in LnFDGS, we propose a numerical method to represent these quantities. Full article

(This article belongs to the Section Gravitation)

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13 pages, 354 KB

Open AccessArticle

Holographic Thermodynamics of Higher-Dimensional AdS Black Holes with CFT Rescaling

by Yahya Ladghami and Taoufik Ouali

Universe 2025, 11(10), 337; https://doi.org/10.3390/universe11100337 - 10 Oct 2025

Viewed by 330

Abstract

In this paper, we study the thermodynamic behavior of charged AdS black holes in higher-dimensional spacetimes within the framework of conformal holographic extended thermodynamics. This formalism is based on a novel AdS/CFT dictionary in which the conformal rescaling factor of the boundary conformal [...] Read more.

In this paper, we study the thermodynamic behavior of charged AdS black holes in higher-dimensional spacetimes within the framework of conformal holographic extended thermodynamics. This formalism is based on a novel AdS/CFT dictionary in which the conformal rescaling factor of the boundary conformal field theory (CFT) is treated as a thermodynamic parameter, while Newton’s constant is held fixed and the AdS radius is allowed to vary. We explore how variations in the CFT state, represented by its central charge, influence the bulk thermodynamics, phase structure, and stability of black holes in five and six dimensions. Our analysis reveals the emergence of Van der Waals-like phase transitions, critical phenomena governed by the central charge. Additionally, we find that the thermodynamic behavior of AdS black holes is affected by the dimensionality of the bulk spacetime, as we compare higher-dimensional black holes to lower-dimensional ones, such as the BTZ black holes. These findings provide new insights into the role of boundary degrees of freedom in shaping the thermodynamics of gravitational systems via holography. Full article

(This article belongs to the Special Issue BGL2025: The 13th Bolyai–Gauss–Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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15 pages, 1215 KB

Open AccessCommunication

Agegraphic Dark Energy from Entropy of the Anti-de Sitter Black Hole

by Qihong Huang, Yang Liu and He Huang

Universe 2025, 11(10), 336; https://doi.org/10.3390/universe11100336 - 10 Oct 2025

Viewed by 335

Abstract

In this paper, we analyze the agegraphic dark energy from the entropy of the anti-de Sitter black hole using the age of the universe as the IR cutoff. We constrain its parameter with the Pantheon+ Type Ia supernova sample and observational Hubble parameter [...] Read more.

In this paper, we analyze the agegraphic dark energy from the entropy of the anti-de Sitter black hole using the age of the universe as the IR cutoff. We constrain its parameter with the Pantheon+ Type Ia supernova sample and observational Hubble parameter data, finding that the Akaike Information Criterion cannot effectively distinguish this model from the standard

Λ

CDM model. The present value of Hubble constant

H_{0}

and the model parameter

b^{2}

are constrained to

H_{0} = 67.7 \pm 1.8

and

b^{2} = 0 . 303_{- 0.024}^{+ 0.019}

. This model realizes the whole evolution of the universe, including the late-time accelerated expansion. Although it asymptotically approaches the standard

Λ

CDM model in the future, statefinder analysis shows that late-time deviations allow the two models to be distinguished. Full article

(This article belongs to the Special Issue Modified Gravity and Dark Energy Theories)

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15 pages, 596 KB

Open AccessArticle

Secular Evolution of a Two-Planet System of Three Bodies with Variable Masses

by Alexander Prokopenya, Mukhtar Minglibayev and Aiken Kosherbayeva

Universe 2025, 11(10), 335; https://doi.org/10.3390/universe11100335 - 10 Oct 2025

Viewed by 219

Abstract

A classical three-body problem with two planets moving around a central star of variable mass on quasi-periodic orbits is considered. The bodies are assumed to attract each other according to Newton’s law of universal gravitation. The star loses its mass anisotropically, and this [...] Read more.

A classical three-body problem with two planets moving around a central star of variable mass on quasi-periodic orbits is considered. The bodies are assumed to attract each other according to Newton’s law of universal gravitation. The star loses its mass anisotropically, and this leads to the appearance of reactive forces. The problem is analyzed in the framework of Newtonian’s formalism, and equations of motion are derived in terms of the osculating elements of aperiodic motion on quasi-conic sections. As equations of motion are not integrable, the perturbation theory is applied with the perturbing forces expanded into power series in terms of eccentricities and inclinations, which are assumed to be small. Averaging these equations over the mean longitudes of the planets in the absence of mean-motion resonances, we obtain the differential equations describing the long-term evolution of orbital elements. Numerical solutions to the evolution equations are obtained and analyzed for three different three-body systems. The obtained results demonstrate clearly that variability of masses may influence essentially the secular evolution of the orbital elements. All the relevant symbolic and numerical calculations are performed with the computer algebra system Wolfram Mathematica. Full article

(This article belongs to the Section Gravitation)

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12 pages, 384 KB

Open AccessArticle

QCD Sum Rule Study of Topped Mesons Within Heavy Quark Effective Theory

by Shu-Wei Zhang, Xuan Luo, Hui-Min Yang and Hua-Xing Chen

Universe 2025, 11(10), 334; https://doi.org/10.3390/universe11100334 - 9 Oct 2025

Viewed by 236

Abstract

Motivated by the recent CMS observation of a near-threshold enhancement in top quark pair production, we investigate a novel class of hadronic systems containing a single top quark: the topped mesons (

t \bar{q}

, with [...] Read more.

Motivated by the recent CMS observation of a near-threshold enhancement in top quark pair production, we investigate a novel class of hadronic systems containing a single top quark: the topped mesons (

t \bar{q}

, with

\bar{q} = \bar{u}, \bar{d}, \bar{s}

). In contrast to the extensively studied toponium (

t \bar{t}

) system—analyzed primarily within perturbative QCD—topped mesons offer a complementary nonperturbative probe of QCD dynamics in the heavy quark limit. These states are expected to exhibit longer lifetimes and narrower decay widths than toponium, as only a single top quark undergoes weak decay. We employ QCD sum rules within the framework of heavy quark effective theory to study the structure and mass spectrum of ground-state topped mesons. Our analysis predicts masses near 173.1 GeV, approximately 0.5–0.6 GeV above the top quark pole mass. Compared with singly topped baryons (

t q q

, with

q = u, d, s

), topped mesons have a simpler quark composition and more favorable decay channels (a topped meson is anticipated to decay weakly into a

Υ

meson and a charmed meson), enhancing their potential for both theoretical analysis and experimental discovery. Full article

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

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18 pages, 2086 KB

Open AccessReview

Jets in Low-Mass Protostars

by Somnath Dutta

Universe 2025, 11(10), 333; https://doi.org/10.3390/universe11100333 - 9 Oct 2025

Viewed by 345

Abstract

Jets and outflows are key components of low-mass star formation, regulating accretion and shaping the surrounding molecular clouds. These flows, traced by molecular species at (sub)millimeter wavelengths (e.g., CO, SiO, SO, H₂CO, and CH₃OH) and by atomic, ionized, and [...] Read more.

Jets and outflows are key components of low-mass star formation, regulating accretion and shaping the surrounding molecular clouds. These flows, traced by molecular species at (sub)millimeter wavelengths (e.g., CO, SiO, SO, H₂CO, and CH₃OH) and by atomic, ionized, and molecular lines in the infrared (e.g., H₂, [Fe II], [S I]), originate from protostellar accretion disks deeply embedded within dusty envelopes. Jets play a crucial role in removing angular momentum from the disk, thereby enabling continued mass accretion, while directly preserving a record of the protostar’s outflow history and potentially providing indirect insights into its accretion history. Recent advances in high-resolution, high-sensitivity observations, particularly with the James Webb Space Telescope (JWST) in the infrared and the Atacama Large Millimeter/submillimeter Array (ALMA) at (sub)millimeter wavelengths, have revolutionized studies of protostellar jets and outflows. These instruments provide complementary views of warm, shock-excited gas and cold molecular component of the jet–outflow system. In this review, we discuss the current status of observational studies that reveal detailed structures, kinematics, and chemical compositions of protostellar jets and outflows. Recent analyses of mass-loss rates, velocities, rotation, molecular abundances, and magnetic fields provide critical insights into jet launching mechanisms, disk evolution, and the potential formation of binary systems and planets. The synergy of JWST’s infrared sensitivity and ALMA’s high-resolution imaging is advancing our understanding of jets and outflows. Future large-scale, high-resolution surveys with these facilities are expected to drive major breakthroughs in outflow research. Full article

(This article belongs to the Special Issue Magnetic Fields and Activity in Stars: Origins and Evolution)

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14 pages, 5542 KB

Open AccessArticle

High-Resolution Infrared Spectroscopy of IRS 16CC and IRS 33N: Stellar Parameters and Implications for Star Formation Near Sgr A^*

by Shogo Nishiyama, Wakana Sato, Moeka Hotta, Momoka Ikarashi, Hiromi Saida, Yohsuke Takamori, Tetsuya Nagata, Hiroyuki Ikeda and Masaaki Takahashi

Universe 2025, 11(10), 332; https://doi.org/10.3390/universe11100332 - 5 Oct 2025

Viewed by 269

Abstract

IRS 16CC and IRS 33N are among more than 100 young, massive stars identified within 0.5 pc from the Galactic central supermassive black hole Sgr A*, where conventional star formation processes are expected to be strongly suppressed. A subset of these stars, including [...] Read more.

IRS 16CC and IRS 33N are among more than 100 young, massive stars identified within 0.5 pc from the Galactic central supermassive black hole Sgr A*, where conventional star formation processes are expected to be strongly suppressed. A subset of these stars, including IRS 16CC, has been confirmed to reside in a clockwise rotating stellar disk, and is thought to have formed in a massive, gaseous disk around Sgr A*. In contrast, other young massive stars, such as IRS 33N, exhibit dynamical behaviors that deviate significantly from those of the disk population, and their formation mechanism is still uncertain. To investigate their formation mechanism, we carried out near-infrared, high-resolution spectroscopic observations of IRS 16CC and IRS 33N using the Infrared Camera and Spectrograph on the Subaru telescope, equipped with an adaptive optics system. We compared the profiles of He I absorption lines with synthetic spectra generated from model atmospheres, and then compared derived stellar parameters with stellar evolutionary tracks to estimate their ages and initial masses. Our analysis yields their effective temperatures of ∼23,000 K, surface gravities of ∼2.8, and initial masses of

37 \pm 6 M_{⊙}

and

27_{- 3}^{+ 4} M_{⊙}

, consistent with spectral types of B0.5–1.5 supergiants. The ages of IRS 16CC and IRS 33N are estimated to be

4.4 \pm 0.7

Myr and

5 . 3_{- 0.7}^{+ 1.1}

Myr, respectively. These results suggest that, despite their different dynamical properties, the two stars are likely to share a common origin. Full article

(This article belongs to the Special Issue 10th Anniversary of Universe: Galaxies and Their Black Holes)

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30 pages, 7521 KB

Open AccessReview

Probing the Sources of Ultra-High-Energy Cosmic Rays—Constraints from Cosmic-Ray Measurements

by Teresa Bister

Universe 2025, 11(10), 331; https://doi.org/10.3390/universe11100331 - 3 Oct 2025

Viewed by 399

Abstract

Ultra-high-energy cosmic rays (UHECRs) are the most energetic particles known—and yet their origin is still an open question. However, with the precision and accumulated statistics of the Pierre Auger Observatory and the Telescope Array, in combination with advancements in theory and modeling—e.g., of [...] Read more.

Ultra-high-energy cosmic rays (UHECRs) are the most energetic particles known—and yet their origin is still an open question. However, with the precision and accumulated statistics of the Pierre Auger Observatory and the Telescope Array, in combination with advancements in theory and modeling—e.g., of the Galactic magnetic field—it is now possible to set solid constraints on the sources of UHECRs. The spectrum and composition measurements above the ankle can be well described by a population of extragalactic, homogeneously distributed sources emitting mostly intermediate-mass nuclei. Additionally, using the observed anisotropy in the arrival directions, namely the large-scale dipole > 8 EeV, as well as smaller-scale warm spots at higher energies, even more powerful constraints on the density and distribution of sources can be placed. Yet, open questions remain—like the striking similarity of the sources that is necessary to describe the rather pure mass composition above the ankle, or the origin of the highest energy events whose tracked back directions point toward voids. The current findings and possible interpretation of UHECR data will be presented in this review. Full article

(This article belongs to the Special Issue Multi-Messenger Astrophysics: Synergies Between Cosmic Rays, Gravitational Waves, Neutrinos, and Electromagnetic Signals)

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16 pages, 1518 KB

Open AccessArticle

Shadow of a Collapsing Star in a Regular Spacetime

by Daniel Nuñez and Juan Carlos Degollado

Universe 2025, 11(10), 330; https://doi.org/10.3390/universe11100330 - 3 Oct 2025

Viewed by 204

Abstract

In this study, we describe the dynamical formation of the shadow of a collapsing star in Hayward spacetime from the points of view of an observer far away from the center and a free-falling observer. By solving the time-like and light-like radial geodesics, [...] Read more.

In this study, we describe the dynamical formation of the shadow of a collapsing star in Hayward spacetime from the points of view of an observer far away from the center and a free-falling observer. By solving the time-like and light-like radial geodesics, we determine the angular size of the shadow as a function of time. We find that the formation of the shadow is a finite process for both observers, and the size of the shadow is affected by the Hayward spacetime parameters. In this study, we consider several scenarios, from the Schwarzschild limit to an extreme Hayward black hole. Full article

(This article belongs to the Section Gravitation)

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27 pages, 1596 KB

Open AccessArticle

The Nuclear Astrophysics Program at the CERN n_TOF Facility: Results and Perspectives

by P. M. Milazzo, C. Lederer-Woods and A. Mengoni

Universe 2025, 11(10), 329; https://doi.org/10.3390/universe11100329 - 30 Sep 2025

Viewed by 402

Abstract

The CERN n_TOF facility is a research infrastructure specifically designed for studying neutron-induced nuclear reactions. Pulsed white neutron beams are delivered toward three experimental areas, two of them at different baselines to apply the time-of-flight technique, and another one very close to the [...] Read more.

The CERN n_TOF facility is a research infrastructure specifically designed for studying neutron-induced nuclear reactions. Pulsed white neutron beams are delivered toward three experimental areas, two of them at different baselines to apply the time-of-flight technique, and another one very close to the neutron source for activation studies. High intensity and high neutron energy resolution make n_TOF a unique facility. A major component of the physics program at n_TOF is dedicated to the measurement of key neutron induced reactions for nuclear astrophysics, relevant to nucleosynthesis in stars, the Big Bang primordial nucleosynthesis as well as Cosmochronology. A review of the relevant results obtained at the n_TOF facility is reported, together with details of challenging new measurements in preparation. Full article

(This article belongs to the Special Issue Advances in Nuclear Astrophysics)

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12 pages, 1328 KB

Open AccessArticle

Long-Term Variations in Background Bias and Magnetic Field Noise in HSOS/SMFT Observations

by Haiqing Xu, Hongqi Zhang, Suo Liu, Jiangtao Su, Yuanyong Deng, Shangbin Yang, Mei Zhang and Jiaben Lin

Universe 2025, 11(10), 328; https://doi.org/10.3390/universe11100328 - 28 Sep 2025

Viewed by 235

Abstract

The Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) has conducted continuous observations of solar vector magnetic fields for nearly four decades, and while the primary optical system remains unchanged, critical components—including filters, polarizers, and detectors—have undergone multiple upgrades and [...] Read more.

The Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station (HSOS) has conducted continuous observations of solar vector magnetic fields for nearly four decades, and while the primary optical system remains unchanged, critical components—including filters, polarizers, and detectors—have undergone multiple upgrades and replacements. Maintaining data consistency is essential for reliable long-term studies of magnetic field evolution and solar activity, as well as current helicity. In this study, we systematically analyze background bias and noise levels in SMFT observations from 1988 to 2019. Our dataset comprises 12,281 vector magnetograms of 1484 active regions. To quantify background bias, we computed mean values of Stokes

Q / I

,

U / I

and

V / I

over each entire magnetogram. The background bias of Stokes

V / I

is small for the whole dataset. The background biases of Stokes

Q / I

and

U / I

fluctuate around zero during 1988–2000. From 2001 to 2011, however, the fluctuations in the background bias of both

Q / I

and

U / I

become significantly larger, exhibiting mixed positive and negative values. Between 2012 and 2019, the background biases shift to predominantly positive values for both Stokes

Q / I

and

U / I

parameters. To address this issue, we propose a potential method for removing the background bias and further discuss its impact on the estimation of current helicity. For each magnetogram, we quantify measurement noise by calculating the standard deviation (

σ

) of the longitudinal (

B_{l}

) and transverse (

B_{t}

) magnetic field components within a quiet-Sun region. The noise levels for

B_{l}

and

B_{t}

components were approximately 15 Gauss (G) and 87 G, respectively, during 1988–2011. Since 2012, these values decreased significantly to ∼6 G for

B_{l}

and ∼55 G for

B_{t}

, likely due to the installation of a new filter. Full article

(This article belongs to the Special Issue Measurements, Observations and Theoretical Studies on the Solar Magnetic Field—Celebrating the 40th Anniversary of the Huairou Solar Observing Station)

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18 pages, 1611 KB

Open AccessReview

Blazars as Probes for Fundamental Physics

by Giorgio Galanti

Universe 2025, 11(10), 327; https://doi.org/10.3390/universe11100327 - 27 Sep 2025

Viewed by 229

Abstract

Blazars are a class of active galactic nuclei characterized by having one of their relativistic jets oriented close to our line of sight. Their broad emission spectrum makes them exceptional laboratories for probing fundamental physics. In this review, we explore the potential impact [...] Read more.

Blazars are a class of active galactic nuclei characterized by having one of their relativistic jets oriented close to our line of sight. Their broad emission spectrum makes them exceptional laboratories for probing fundamental physics. In this review, we explore the potential impact on blazar observations of three scenarios beyond the standard paradigm: (i) the hadron beam model, (ii) the interaction of photons with axion-like particles (ALPs), and (iii) Lorentz invariance violation. We focus on the very-high-energy spectral features these scenarios induce in the blazars Markarian 501 and 1ES 0229+200, making them ideal targets for testing such effects. Additionally, we examine ALP-induced effects on the polarization of UV-X-ray and high-energy photons from the blazar OJ 287. The unique signatures produced by these models are accessible to current and upcoming instruments—such as the ASTRI Mini Array, CTAO, LHAASO, IXPE, COSI, and AMEGO—offering new opportunities to probe and constrain fundamental physics through blazar observations. Full article

(This article belongs to the Special Issue Multi-wavelength Properties of Active Galactic Nuclei)

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11 pages, 210 KB

Open AccessCommunication

Toward a Reliability Scale for Assessing Reports of Unidentified Anomalous Phenomena (UAP)

by Dirk Schulze-Makuch and Tony Reichhardt

Universe 2025, 11(10), 326; https://doi.org/10.3390/universe11100326 - 25 Sep 2025

Viewed by 765

Abstract

Unidentified Anomalous Phenomena (UAP) observations have been reported from ancient times to today, but their true nature remains uncertain. In this paper we propose a rating scale designed to separate “signal” from “noise” in assessing UAP sighting reports. Our intention is that this [...] Read more.

Unidentified Anomalous Phenomena (UAP) observations have been reported from ancient times to today, but their true nature remains uncertain. In this paper we propose a rating scale designed to separate “signal” from “noise” in assessing UAP sighting reports. Our intention is that this will help professionals and laypeople alike distinguish cases that warrant further investigation from easily explainable false alarms. We categorize UAP sighting reports according to the quality of their evidence, considering such factors as number of observers, amount and quality of supporting evidence, especially physical evidence, and perhaps most importantly, whether UAP witnesses have made some effort to find an ordinary explanation for what they saw or experienced and whether the evidence has been subject to expert analysis. Full article

35 pages, 580 KB

Open AccessArticle

Quadrupole Perturbations of Slowly Spinning Ellis–Bronnikov Wormholes

by Bahareh Azad, Jose Luis Blázquez-Salcedo, Fech Scen Khoo, Jutta Kunz and Francisco Navarro-Lérida

Universe 2025, 11(10), 325; https://doi.org/10.3390/universe11100325 - 24 Sep 2025

Viewed by 781

Abstract

We study the axial and polar perturbations of slowly rotating Ellis–Bronnikov wormholes in General Relativity, applying a perturbative double expansion. In particular, we derive the equations for

l = 2

,

M_{z} = 2

perturbations of these objects, which are parametrized by [...] Read more.

We study the axial and polar perturbations of slowly rotating Ellis–Bronnikov wormholes in General Relativity, applying a perturbative double expansion. In particular, we derive the equations for

l = 2

,

M_{z} = 2

perturbations of these objects, which are parametrized by an asymmetry parameter. The equations constitute an astrophysically interesting sector of the perturbations that contribute dominantly to the gravitational wave radiation. Moreover, calculation of these modes may exhibit potential instabilities in the quadrupole sector. Full article

(This article belongs to the Special Issue Experimental and Observational Constraints on Wormhole Models)

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15 pages, 356 KB

Open AccessArticle

Energy–Momentum Squared Gravity Attached with Perfect Fluid Admitting Conformal Ricci Solitons

by Mohd Danish Siddiqi and Ibrahim Al-Dayel

Universe 2025, 11(10), 324; https://doi.org/10.3390/universe11100324 - 24 Sep 2025

Viewed by 337

Abstract

In the present research note, we explore the nature of the conformal Ricci solitons on the energy–momentum squared gravity model

F (R, T^{2})

that is a modification of general relativity. Furthermore, we deal with a subcase of the [...] Read more.

In the present research note, we explore the nature of the conformal Ricci solitons on the energy–momentum squared gravity model

F (R, T^{2})

that is a modification of general relativity. Furthermore, we deal with a subcase of the

F (R, T^{2}) = R + λ T^{2}

-gravity model coupled with a perfect fluid, which admits conformal Ricci solitons with a time-like concircular vector field. Using the steady conformal Ricci soliton, we derive the equation of state for the perfect fluid in the

F (R, T^{2})

-gravity model. In this series, we convey an indication of the pressure and density in the phantom barrier period and the stiff matter era, respectively. Finally, using a conformal Ricci soliton with a concircular vector field, we study the various energy constraints, black holes, and singularity circumstances for a perfect fluid coupled to

F (R, T^{2})

-gravity. Lastly, employing conformal Ricci solitons, we formulate the first law of thermodynamics, enthalpy, and the particle production rate in

F (R, T^{2})

-gravity and orthodox gravity. Full article

(This article belongs to the Section Gravitation)

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