Physics of the Dark Universe最新文献

{"title":"Quantum-corrected thermodynamics and plasma lensing in non-minimally coupled symmetric teleparallel black holes","authors":"Erdem Sucu ,&nbsp;İzzet Sakallı ,&nbsp;Özcan Sert ,&nbsp;Yusuf Sucu","doi":"10.1016/j.dark.2025.102063","DOIUrl":"10.1016/j.dark.2025.102063","url":null,"abstract":"<div><div>We investigate the thermodynamic and optical signatures of electrically charged black holes (BHs) in symmetric teleparallel gravity (STPG) with non-minimal electromagnetic coupling, incorporating quantum corrections and plasma dispersion effects. The BH solution, characterized by a coupling parameter <span><math><mi>k</mi></math></span>, generalizes the Reissner–Nordström spacetime through power-law modifications to electromagnetic terms in the metric function. We implement exponential corrections to the Bekenstein–Hawking entropy of the form <span><math><mrow><mi>S</mi><mo>=</mo><msub><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>+</mo><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo><msub><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msub></mrow></msup></mrow></math></span> and derive quantum-corrected expressions for fundamental thermodynamic quantities including internal energy, Helmholtz and Gibbs free energies, pressure, enthalpy, and heat capacity. Our analysis reveals rich phase transition structures with second-order transitions occurring at critical horizon radii for specific coupling values, demonstrating enhanced thermodynamic instability under strong non-minimal coupling effects. The quantum-corrected Joule–Thomson expansion analysis identifies distinct cooling and heating regimes separated by inversion points that shift systematically with the coupling parameter <span><math><mi>k</mi></math></span>. We analyze the efficiency of heat engines operating in Carnot cycles, finding that electromagnetic charge enhances thermodynamic performance with efficiency values approaching 99% for optimal configurations in this geometry. Using the Gauss–Bonnet theorem, we derive analytical expressions for gravitational deflection angles in both vacuum and plasma environments, revealing how non-minimal coupling and plasma dispersion create frequency-dependent lensing signatures that differ substantially from general relativity predictions.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102063"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144912936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lorentz-violating ModMax black holes in phantom-enhanced Kalb–Ramond gravity: Thermodynamics and topological charges","authors":"Y. Sekhmani ,&nbsp;S.K. Maurya ,&nbsp;J. Rayimbaev ,&nbsp;M. Altanji ,&nbsp;I. Ibragimov ,&nbsp;S. Muminov","doi":"10.1016/j.dark.2025.102079","DOIUrl":"10.1016/j.dark.2025.102079","url":null,"abstract":"<div><div>We derive exact static, spherically symmetric black hole (BH) solutions within the framework of four-dimensional Einstein gravity, coupled to ModMax nonlinear electrodynamics and a Kalb–Ramond two-form. This coupling is governed by a discrete sign parameter, denoted as <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>±</mo><mn>1</mn></mrow></math></span>. In the ”ordinary” branch (<span><math><mrow><mi>ζ</mi><mo>=</mo><mo>+</mo><mn>1</mn></mrow></math></span>), the metric features both Cauchy and event horizons, while the electromagnetic stress–energy adheres to all classical energy conditions. In contrast, the ”phantom” branch (<span><math><mrow><mi>ζ</mi><mo>=</mo><mo>−</mo><mn>1</mn></mrow></math></span>) accommodates only a single horizon and simultaneously violates the weak, null, and strong conditions, which reflects genuine ghost-matter behaviour. The thermodynamic behaviour for <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>+</mo><mn>1</mn></mrow></math></span> results in multiple divergences in heat capacity and presents a distinctive swallowtail pattern in the AdS Gibbs free energy, indicative of a first-order phase transition that encompasses small, intermediate, and large phases. In contrast, for <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>−</mo><mn>1</mn></mrow></math></span>, there is only a single divergence observed, accompanied by a smooth Gibbs curve with no van der Waals-type oscillatory behaviour, which precludes the possibility of true coexistence. Topological analysis using Duan’s <span><math><mi>φ</mi></math></span>-mapping in AdS further differentiates the branches by examining their winding numbers. For <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>+</mo><mn>1</mn></mrow></math></span>, the winding numbers are <span><math><mrow><mo>(</mo><mo>+</mo><mn>1</mn><mo>,</mo><mo>−</mo><mn>1</mn><mo>,</mo><mo>+</mo><mn>1</mn><mo>)</mo></mrow></math></span>, resulting in a total topological charge (net winding number) of <span><math><mrow><mi>W</mi><mo>=</mo><mo>+</mo><mn>1</mn></mrow></math></span>. In contrast, for <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>−</mo><mn>1</mn></mrow></math></span>, the winding numbers are <span><math><mrow><mo>(</mo><mo>−</mo><mn>1</mn><mo>,</mo><mo>+</mo><mn>1</mn><mo>)</mo></mrow></math></span>, leading to a total topological charge of <span><math><mrow><mi>W</mi><mo>=</mo><mn>0</mn></mrow></math></span>. This distinction assigns a clear topological charge, which differentiates between the first-order transitions associated with <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>+</mo><mn>1</mn></mrow></math></span> and the smooth, latent-heat-free phase changes linked to <span><math><mrow><mi>ζ</mi><mo>=</mo><mo>−</mo><mn>1</mn></mrow></math></span>. Overall, <span><math><mi>ζ</mi></math></span> serves as the primary determinant influencing causal structure, energy condition profiles, critical phenomena, and topological charge in ModMax-Kalb-Ramond BH.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102079"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145060593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Possible formation of traversable wormholes and their thermodynamic analysis in F(Q,Lm,T) gravity","authors":"Rounak Manna,&nbsp;Krishna Pada Das,&nbsp;Ujjal Debnath","doi":"10.1016/j.dark.2025.102142","DOIUrl":"10.1016/j.dark.2025.102142","url":null,"abstract":"<div><div>In this work, we investigate static and spherically symmetric traversable wormhole solutions within the framework of the extended symmetric teleparallel gravity, specifically the <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>Q</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></mrow></math></span> gravity theory, where <span><math><mi>Q</mi></math></span>, <span><math><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>, and <span><math><mi>T</mi></math></span> are the respective representations of the non-metricity scalar, the matter Lagrangian, and the trace of the energy–momentum tensor. By employing a specific redshift function and deriving the shape function through the Karmarkar condition, we examine the fundamental geometric features required for a viable wormhole structure. The analysis confirms the satisfaction of key conditions such as the throat condition, flaring-out condition, and asymptotic flatness. A detailed study of energy conditions for various values of model parameters reveals that the null energy condition and averaged null energy condition are violated near the throat, indicating the presence of exotic matter. Additionally, thermodynamic quantities such as temperature, pressure, specific heat, work density, and energy flux are analyzed, all of which support the thermal and equilibrium stability of the wormhole. Our findings demonstrate that even in extended theories like <span><math><mrow><mi>F</mi><mrow><mo>(</mo><mi>Q</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></mrow></math></span> gravity, exotic matter remains essential for sustaining traversable wormholes. This work lays the foundation for further investigations into their stability under dynamical perturbations and potential astrophysical implications.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102142"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145415948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cosmological perturbations of extended NGR model with parity violation","authors":"Yuxuan Kang,&nbsp;Mingzhe Li,&nbsp;Yeheng Tong","doi":"10.1016/j.dark.2025.102148","DOIUrl":"10.1016/j.dark.2025.102148","url":null,"abstract":"<div><div>Recently the modified teleparallel gravity models attracted a lot of interests. In this paper we consider more extensions to the New General Relativity (NGR) model with parity violations. This extended NGR model differs from the normal NGR model by the inclusion of additional parity-odd term that is quadratic in the torsion tensor. By investigating its cosmological perturbations of this model, we find that this model can avoid ghost instabilities in certain regions of the parameter space, where the coefficient of the parity-odd term does not vanish.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102148"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145415951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Particle dynamics and thermal properties in Kalb–Ramond ModMax black holes: Theoretical predictions for observational tests of exotic physics","authors":"Ahmad Al-Badawi ,&nbsp;Faizuddin Ahmed ,&nbsp;İzzet Sakallı","doi":"10.1016/j.dark.2025.102076","DOIUrl":"10.1016/j.dark.2025.102076","url":null,"abstract":"<div><div>We present a comprehensive theoretical study of geodesic motion and thermodynamic behavior in Kalb–Ramond (KR) black hole (BH) spacetimes sourced by ModMax electrodynamics. Both neutral and charged test particle dynamics are investigated, highlighting how the Lorentz symmetry breaking (LSB) parameter <span><math><mi>ℓ</mi></math></span>, the ModMax nonlinearity parameter <span><math><mi>γ</mi></math></span>, and the discrete branch parameter <span><math><mi>ζ</mi></math></span> significantly modify orbital structures compared to classical Schwarzschild and Reissner–Nordström (RN) solutions. Effective potential analysis reveals notable shifts in the innermost stable circular orbit (ISCO): ordinary branches allow stable orbits closer to the horizon, while phantom branches shift them outward by factors of 5–10. For charged particles, the combined influence of modified gravity and nonlinear electromagnetic fields may induce chaotic trajectories in certain regimes. On the thermodynamic side, we derive full expressions for Hawking temperature, entropy, and Helmholtz free energy. Ordinary branches exhibit divergent specific heat indicating second-order phase transitions, whereas phantom branches yield consistently negative specific heat, implying thermal instability. Phantom BHs are found to possess higher Hawking temperatures and show distinct thermodynamic phase structures, including Hawking–Page-type transitions. Observational features such as BH shadows and gravitational lensing are explored, revealing parameter-dependent changes in photon sphere radii and deflection angles. Notably, the deflection angle analysis via the Gauss–Bonnet theorem method (GBTm) shows opposite-sign electromagnetic corrections for phantom versus ordinary branches, suggesting potential observational discriminants.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102076"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145109404","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From geometry to observation: Gravitational waves and the Raychaudhuri equation","authors":"Sougata Bhunia ,&nbsp;Anubhab Dutta ,&nbsp;Debashis Gangopadhyay ,&nbsp;Goutam Manna","doi":"10.1016/j.dark.2025.102089","DOIUrl":"10.1016/j.dark.2025.102089","url":null,"abstract":"<div><div>Gravitational waves (GWs) are independent of any particular theory of gravity. The universality of this notion is highlighted by the Raychaudhuri equation (RE), which is independent of any theory of gravity and contains the Ricci tensor <span><math><msub><mrow><mi>R</mi></mrow><mrow><mi>μ</mi><mi>ν</mi></mrow></msub></math></span> as a key ingredient, thereby connecting spacetime geometry with matter-energy content. Under small metric perturbations, <span><math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mi>μ</mi><mi>ν</mi></mrow></msub><mo>∝</mo><mo>□</mo><msub><mrow><mi>h</mi></mrow><mrow><mi>μ</mi><mi>ν</mi></mrow></msub></mrow></math></span>, where <span><math><msub><mrow><mi>h</mi></mrow><mrow><mi>μ</mi><mi>ν</mi></mrow></msub></math></span> is the perturbation, indicating that various gravity theories, via their corresponding <span><math><msub><mrow><mi>R</mi></mrow><mrow><mi>μ</mi><mi>ν</mi></mrow></msub></math></span>, produce different gravitational wave equations. In the framework of Einstein’s gravity, this leads to the standard wave equation. This study analyzes a modified form, <em>GW-inspired RE</em>, within the homogeneous and isotropic FLRW background to investigate late-time cosmic acceleration and structure formation. We employ <em>Pantheon+ SNe Ia, Hubble, and BAO</em> datasets to constrain model parameters through Bayesian inference utilizing NUTS in <em>NumPyro</em>. A nuisance parameter <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span> is introduced to address residual systematics. This facilitates a robust estimation of <span><math><msub><mrow><mi>H</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>, <span><math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>D</mi><mi>E</mi><mo>,</mo><mn>0</mn></mrow></msub></math></span>, and <span><math><msub><mrow><mi>r</mi></mrow><mrow><mi>d</mi></mrow></msub></math></span>, which addresses the resolution of the Hubble tension. We analyze the redshift evolution of the deceleration parameter, <span><math><mrow><mi>q</mi><mrow><mo>(</mo><mi>z</mi><mo>)</mo></mrow></mrow></math></span>, both with and without <span><math><msub><mrow><mi>μ</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>, emphasizing its influence on cosmic dynamics. The GW-inspired RE is reformulated as a harmonic oscillator, providing insight into expansion and geodesic focusing. A graphical comparison demonstrates the relationship <span><math><mrow><msubsup><mrow><mi>d</mi></mrow><mrow><mi>L</mi></mrow><mrow><mi>G</mi><mi>W</mi></mrow></msubsup><mrow><mo>(</mo><mi>z</mi><mo>)</mo></mrow><mo>=</mo><msubsup><mrow><mi>d</mi></mrow><mrow><mi>L</mi></mrow><mrow><mi>E</mi><mi>M</mi></mrow></msubsup><mrow><mo>(</mo><mi>z</mi><mo>)</mo></mrow></mrow></math></span> utilizing GWOSC data. Thus, the RE in the context of small perturbation of the metric opens up whole new vistas of <em>observational astronomy.</em></div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102089"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145105824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Traversable wormholes in non-minimal Einstein–Yang–Mills gravity: Geometry, energy conditions, and gravitational lensing","authors":"Jureeporn Yuennan ,&nbsp;Allah Ditta ,&nbsp;Thammarong Eadkhong ,&nbsp;Phongpichit Channuie","doi":"10.1016/j.dark.2025.102091","DOIUrl":"10.1016/j.dark.2025.102091","url":null,"abstract":"<div><div>This work presents a new class of static, spherically symmetric traversable wormhole solutions within the framework of non-minimal Einstein–Yang–Mills (EYM) gravity, where the SU(2) Yang–Mills field is purely magnetic. By adopting a constant redshift function and introducing a direct coupling between the Ricci scalar and the Yang–Mills field strength, we investigate the role of the non-minimal coupling constant <span><math><mi>ξ</mi></math></span> and the magnetic charge <span><math><mi>Q</mi></math></span> in shaping the wormhole geometry. Our analysis shows that for small values of <span><math><mi>ξ</mi></math></span>, the flare-out and throat conditions can be satisfied, allowing physically viable traversable wormholes without requiring externally introduced exotic matter. The Arnowitt–Deser–Misner (ADM) mass is evaluated, revealing that for <span><math><mrow><mi>ξ</mi><mo>&lt;</mo><mn>0</mn><mo>.</mo><mn>01</mn></mrow></math></span> it grows monotonically with charge, whereas for <span><math><mrow><mi>ξ</mi><mo>≳</mo><mn>0</mn><mo>.</mo><mn>01</mn></mrow></math></span> it decreases with increasing charge, signaling a reduction in the total mass-energy of the system. An examination of the energy conditions indicates localized violations of the null and weak energy conditions at the throat, while the strong energy condition remains satisfied. Finally, the study of gravitational lensing confirms that the deflection angle of light is consistently positive, reflecting the overall attractive nature of the wormhole’s gravitational field. These results highlight the significant role of non-minimal gauge–gravity couplings in enabling traversable wormholes with distinct observational signatures.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102091"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145105928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"f(Q,Lm) gravity, and its cosmological implications","authors":"Ayush Hazarika ,&nbsp;Simran Arora ,&nbsp;P.K. Sahoo ,&nbsp;Tiberiu Harko","doi":"10.1016/j.dark.2025.102092","DOIUrl":"10.1016/j.dark.2025.102092","url":null,"abstract":"<div><div>Symmetric teleparallel gravity and its <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>)</mo></mrow></mrow></math></span> extensions have emerged as promising alternatives to General Relativity (GR), yet the role of explicit geometry–matter couplings remains largely unexplored. In this work, we address this gap by proposing a generalized <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span> theory, where the gravitational Lagrangian density depends on both the non-metricity scalar <span><math><mi>Q</mi></math></span> and the matter Lagrangian <span><math><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub></math></span>. This formulation naturally includes Coincident GR and the Symmetric Teleparallel Equivalent of GR as special cases. Working in the metric formalism, we derive the corresponding field equations, which generalize those of the standard <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>)</mo></mrow></mrow></math></span> gravity, and obtain the modified Klein–Gordon equation for scenarios involving scalar fields. The cosmological implications of the theory are explored in the context of the Friedmann–Lemaître–Robertson–Walker (FLRW) universe. As a first step, we obtain the modified Friedmann equations for <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span> gravity in full generality. We then investigate specific cosmological models arising from both linear and non-linear choices of <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>Q</mi><mo>,</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>m</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span>, performing detailed comparisons with the standard <span><math><mi>Λ</mi></math></span>CDM scenario and examining their observational consequences.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102092"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145105931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Machine learning-based analytical expressions for Gray-Body Factors and application to Primordial Black Holes","authors":"Guan-Wen Yuan ,&nbsp;Marco Calzà ,&nbsp;Davide Pedrotti","doi":"10.1016/j.dark.2025.102078","DOIUrl":"10.1016/j.dark.2025.102078","url":null,"abstract":"<div><div>Symbolic Regression (SR) is a machine learning approach that explores the space of mathematical expressions to identify those that best fit a given dataset, balancing both accuracy and simplicity. We apply SR to the study of Gray-Body Factors (GBFs), which play a crucial role in the derivation of Hawking radiation and are recognized for their computational complexity. We explore simple analytical forms for the GBFs of the Schwarzschild Black Hole (BH). We compare the results obtained with different approaches and quantify their consistency with those obtained by solving the Teukolsky equation. As a case study, we apply our pipeline, which we call <span>ReGrayssion</span>, to the study of Primordial Black Holes (PBHs) as Dark Matter (DM) candidates, deriving constraints on the abundance from observations of diffuse extragalactic <span><math><mi>γ</mi></math></span>-ray background. These results highlight the possible role of SR in providing human-interpretable, approximate analytical GBF expressions, offering a new pathway for investigating PBH as a DM candidate.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102078"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145050091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamics of charged-spinning particles around charged Kalb–Ramond black holes","authors":"Shokhzod Jumaniyozov ,&nbsp;Javlon Rayimbaev ,&nbsp;Munisbek Akhmedov ,&nbsp;Yunus Turaev ,&nbsp;Sulton Usanov ,&nbsp;Satimbay Palvanov","doi":"10.1016/j.dark.2025.102161","DOIUrl":"10.1016/j.dark.2025.102161","url":null,"abstract":"<div><div>This work examines the dynamics of charged spinning test particles in the spacetime of a charged Kalb–Ramond (KR) black hole, characterized by its mass, electric charge, and a Lorentz symmetry-breaking parameter. The equations of motion for spinning, charged particles are derived using the Mathisson–Papapetrou–Dixon (MPD) equations, which incorporate both spin–curvature coupling and electromagnetic interactions. Using the spacetime’s symmetries, we obtain conserved quantities such as energy and angular momentum and employ them to construct the effective potential governing radial motion. The analysis focuses on circular trajectories and the properties of the innermost stable circular orbits (ISCOs), emphasizing how particle spin, black hole charge, and the Lorentz symmetry-breaking parameter modify orbital stability. Our results show that increases in spin and electric charge significantly alter the location of ISCOs. At the same time, the Lorentz symmetry-breaking parameter shifts the effective potential and changes the binding energy of orbits. Beyond orbital motion, we investigate high-energy processes by analyzing collisions of charged spinning particles near the event horizon. The conditions for reaching critical angular momentum are determined, and the resulting center-of-mass energy is computed. We demonstrate that the interplay between spin, electromagnetic interactions, and spacetime modifications can enhance collision energies, potentially producing signatures relevant for astrophysical observations. The study also addresses the emergence of superluminal motion in extreme regimes and identifies the bounds necessary for physically admissible trajectories. Overall, the results highlight how spin, charge, and KR corrections jointly shape particle dynamics, providing potential observational imprints of modified gravity in strong-field environments.</div></div>","PeriodicalId":48774,"journal":{"name":"Physics of the Dark Universe","volume":"50 ","pages":"Article 102161"},"PeriodicalIF":6.4,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145528680","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}