The Giant Dipole Resonance (GDR) in 51V has been a long-term conflicting interpretation, with existing photoneutron cross section data suggesting either a single peak or a pronounced splitting, leading to opposite conclusions on nuclear deformation. A new measurement of the 51V( <italic>&#947;</italic>,1n) cross section, performed at the Shanghai Laser Electron Gamma Source (SLEGS) facility, employs a refined monochromatic cross section extraction method. By integrating Polynomial Regression and Support Vector Regression (SVR) for robust interpolation and extrapolation, the new extracted monoenergetic cross sections exhibit a single, broad peak with no evidence of GDR splitting. Re-analysis of the reported splitting shows that any deformation extracted from such a structure would be relatively weaker than those of neighboring nuclei, providing a support for a spherical or near-spherical shape of 51V. Furthermore, we found that deliberately overfitting the data using an SVR model reproduces multi-peak structures similar to those reported in historical datasets, implying that the previously claimed splitting might originated from analysis artifacts rather than physical phenomena.

China

Zi-Rui Hao

Gong-Tao Fan

Chen Chen

Qian-Kun Sun

Hong-Wei Wang

Yi-Fei Niu

Hang-Hua Xu

Long-Xiang Liu

Yue Zhang

Yu-Xuan Yang

Kai-Jie Chen

Zhi-Cai Li

Pu Jiao

Meng-Die Zhou

Shan Ye

Zhen-Wei Wang

Xiang-Fei Wang

Meng-Ke Xu

Yu-Long Shen

Chang Yang

Jia-Wen Ding

New measurement of 51V( <italic>&#947;</italic>,1n) cross section through the refined monochromatic cross section extraction method

We investigate the thermodynamic behavior of a spherically symmetric Anti-de Sitter black hole in Mod(A)Max electrodynamics surrounded by a cloud of strings. Within the extended phase-space framework, we treat the cosmological constant as a pressure and interpret the black-hole mass as enthalpy, which enables a unified discussion of local stability, global phase structure, and Joule–Thomson expansion. We analyze the Hawking temperature, Gibbs free energy, and heat capacity, and show how the string-cloud parameter, the Mod(A)Max deformation, and the electric charge reshape the physical domain, the stability windows, and the small/large black-hole transition pattern. We further characterize the critical behavior and demonstrate that a van der Waals–like phase structure arises only in the physical sector, while the alternate branch does not admit a genuine critical point. For the Joule-Thomson process, we determine the inversion curve and the corresponding isenthalpic trajectories, highlighting how the model parameters control the cooling/heating regimes and can generate terminating isenthalpic behavior at sufficiently large charge. Finally, we examine the sparsity of Hawking radiation and discuss how the underlying parameters influence the temporal discreteness of the emitted flux, particularly near extremality and in the large-radius AdS regime.

India

Faizuddin Ahmed

Jordan

Ahmad Al-Badawi

Brazil

Edilberto O. Silva

Thermal analysis, Joule-Thomson expansion and Hawking sparsity of Mod(A)Max-AdS black hole immersed in a cloud of strings

In this paper, we investigate the shadow and optical appearance of the Bardeen black hole surrounded by perfect fluid dark matter (PFDM) illuminated by various static accretions. First, we find that as the dark matter parameter | <italic>&#945;</italic>| increases, the fundamental characteristic quantities of the black hole, the event horizon <italic>r<inf>h</inf></italic>, the photon sphere radius <italic>r<inf>ph</inf></italic>, and the critical impact parameter <italic>b<inf>ph</inf></italic> all increase, while the peak of the effective potential <italic>V</italic> <inf>eff</inf> decreases and shifts toward the direction of increasing <italic>r</italic>. In contrast, the magnetic charge parameter <italic>g</italic> suppresses <italic>r<inf>h</inf>, r<inf>ph</inf></italic>, and <italic>b<inf>ph</inf></italic>, while increases the peak of <italic>V</italic> <inf>eff</inf> and shifts it toward the direction of decreasing <italic>r</italic>. This indicates a competing effect between the dark matter parameter | <italic>&#945;</italic>| and the magnetic charge parameter <italic>g</italic> on the fundamental properties of the black hole. Furthermore, we use the EHT observational data to constrain the dark matter parameters <italic>&#945;</italic> and find that the constraint range given by the supermassive black hole SgrA* is stricter than that of the black hole M87*. Finally, we investigate black hole images under different accretion models. The results reveal that both dark matter parameters <italic>&#945;</italic> and accretion models significantly influence the black hole images. For larger dark matter parameters | <italic>&#945;</italic>|, the inner shadow or central faint illuminating region of the Bardeen black hole surrounded by PFDM is larger, but the bright ring of the image is fainter. This provides a potential method for us to distinguish between classical Bardeen black holes and Bardeen black holes surrounded by PFDM. These preliminary results may provide some clues for future investigations of dark matter using black hole shadows and images.

Hui Zeng

Yuan Meng

Images from disk and spherical accretions of Bardeen black hole surrounded by perfect fluid dark matter

We explore black hole solutions in the context of Born-Infeld- <italic>f</italic>( <italic>R</italic>) gravity, a modified gravitational framework that extends both Born-Infeld and <italic>f</italic>( <italic>R</italic>) theories. By adopting a static, spherically symmetric spacetime ansatz, we derive an exact black hole solution and investigate its geometrical structure. We proceed to analyze the thermodynamic properties of the solution, including the Hawking temperature, entropy, and specific heat, with particular emphasis on their dependence on the model parameters. Our results reveal novel thermodynamic behavior that deviates significantly from the standard predictions of general relativity. A comparative study with the Schwarzschild-AdS black holes is also presented, showing how Born-Infeld- <italic>f</italic>( <italic>R</italic>) corrections alter black hole thermodynamics.

Türkiye

Salih Kibaroğlu

Born–Infeld- <italic>f</italic>( <italic>R</italic>) black holes

We show that black holes and the evolving universe belong to fundamentally different thermodynamic regimes: while stationary black holes obey ordinary Bekenstein-Hawking thermodynamics, cosmology follows memory-bearing teleodynamics, which is also inevitable for non-stationary black holes. This provides a dynamical, semi-classical realization of the thermodynamic split conjecture and identifies memory accumulation as the natural source of deviations from the area law in cosmology. Our results suggest that quantum gravity constructions should not seek to extrapolate black hole thermodynamics to the universe, but instead perhaps incorporate horizon memory as a fundamental microscopic ingredient and consider cosmological constructions consistent with that.

United States

Oem Trivedi

Venkat Venkatasubramanian

Thermodynamics vs teleodynamics: A cosmological divide?

The ACT data have severely constrained the single scalar field models. Known models of inflation, like the Starobinsky model, the Higgs model and the <italic>a</italic>-attractors are at least 2 <italic>&#963;</italic> off the ACT data. In this work we aim to provide a top-to-bottom approach in single scalar field inflationary cosmology compatible with the ACT data. Specifically, inspired by the fact that the Starobinsky model, the Higgs model and the <italic>a</italic>-attractors, all being plateau potentials, result to the same attractor relation between the spectral index of scalar perturbations and the tensor-to-scalar ratio, which is of the form <math altimg='si7.svg'><mrow><msub><mi>n</mi><mi>s</mi></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mn>1</mn><mo linebreak='goodbreak'>&#8722;</mo><mi>&#945;</mi><msup><mi>r</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></math>, in this work we seek for attractors of the form <math altimg='si8.svg'><mrow><msub><mi>n</mi><mi>s</mi></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>f</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math> that may lead to ACT-compatible inflation. Specifically, we fix the function <italic>f</italic>( <italic>r</italic>) to have a specific desirable form and then solve the differential equation <math altimg='si8.svg'><mrow><msub><mi>n</mi><mi>s</mi></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>f</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math> to find the potential which results to the relation <math altimg='si8.svg'><mrow><msub><mi>n</mi><mi>s</mi></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>f</mi><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow></mrow></math>. We discovered analytically three classes of potentials which are variants of the general form <math altimg='si9.svg'><mrow><msub><mi>n</mi><mi>s</mi></msub><mrow><mo>(</mo><mi>r</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mi>&#947;</mi><mo>&#177;</mo><mi>&#946;</mi><mi>r</mi><mo>&#177;</mo><msup><mi>r</mi><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></mrow></math> and all these models are found to be compatible with the ACT data.

Greece

Azerbaijan

V.K. Oikonomou

General scalar field inflation ACT attractors: Utilizing the <italic>n<inf>s</inf></italic>( <italic>r</italic>) relation

Lee-Yang zero theory plays a crucial role in phase transition theory and is widely employed in the critical behavior of statistical thermodynamics. The supercritical regime of black hole thermodynamics remains a relatively unexplored area, and recent applications of this theory to charged anti-de Sitter (AdS) black holes have initiated probes into this regime, revealing a simple structure partitioned by a single Widom line. In this paper, we apply Lee-Yang theory to charged Gauss-Bonnet AdS black holes, which feature complex phase diagrams (e.g., triple points), to determine how such structures are reflected in the supercritical regime. Notably, we observe a key dimensional difference in that the five-dimensional (5d) system, which lacks a triple point, confirms the known single Widom line structure, while the six-dimensional (6d) system, which admits a triple point, generates two distinct Widom lines. These lines partition the supercritical domain into three sectors (small-, intermediate-, and large- black hole-like phases), corresponding to the three phases coexisting at the triple point. Our results reveal a direct correspondence between the number of coexisting phases at a triple point and the number of distinct supercritical sectors separated by Widom lines.

Zhi-Yuan Li

Xuan-Rui Chen

Bin Wu

Zhen-Ming Xu

Thermodynamic supercriticality and complex phase diagram for charged Gauss-Bonnet AdS black holes

In this study, we explore how photons move around slowly rotating wormholes, maintained by the subtle interplay of non-commutative geometry and Casimir vacuum energy. Our aim is to understand how quantum-corrected redshift profiles and rotation influence photon-sphere locations and shape the shadows an observer would see. Photon spheres—where light can orbit at a fixed radius—are highly sensitive to the wormhole’s gravitational structure. Quantum effects from non-commutative smearing and Casimir energy gently modify the gravitational potential near the throat, leading to small but meaningful shifts in the photon-sphere radius. Gaussian smearing produces mild inward shifts, nonlocal gamma-type profiles spread corrections over a broader region, and Lorentzian profiles, concentrated near the throat, generate the largest deviations. Rotation introduces frame-dragging effects, subtly pulling co-rotating photons inward while pushing counter-rotating photons outward, resulting in two closely spaced photon rings. The impact of this splitting depends on the wormhole’s angular momentum and the steepness of the quantum-corrected redshift, with Lorentzian profiles creating the most noticeable asymmetry. Consequently, the shadow’s shape reflects these effects: Gaussian profiles yield nearly circular shadows, gamma-type profiles produce moderate asymmetry, and Lorentzian profiles generate the most pronounced distortions. The quantum energy density and radial violation of the null energy condition stabilize the throat and determine photon-sphere positions. Together, quantum smearing, Casimir energy, and slow rotation encode subtle directional biases in photon paths, shaping the wormhole’s visible shadow. In essence, quantum effects set the gravitational stage, while rotation adds a delicate directional twist, together crafting the wormhole’s observable signature.

South Africa

A. Errehymy

M. Govender

Oman

S.K. Maurya

K.N. Singh

Kazakhstan

B. Myrzakulova

Uzbekistan

J. Rayimbaev

M. Vapayev

Quantum-corrected slowly rotating wormholes: Frame dragging, photon rings, and shadows

We construct static, spherically symmetric black hole solutions in Einstein gravity coupled to a hidden <italic>U</italic>(1) vector (dark photon), treating both a minimal massive-vector sector and the phenomenologically standard kinetically mixed Einstein-Maxwell-Proca theory. A key ingredient is a clean separation between (i) the <italic>source</italic> density that enters the Helmholtz (Proca) equation and (ii) the <italic>field</italic> energy density and pressures that gravitate in Einstein&#8217;s equations. In the Einstein-Proca setup, the exterior Yukawa profile <math altimg='si17.svg'><mrow><mo>&#8733;</mo><msup><mi>e</mi><mrow><mo>&#8722;</mo><msub><mi>m</mi><mi>X</mi></msub><mi>r</mi></mrow></msup><mo linebreak='goodbreak'>/</mo><mi>r</mi></mrow></math> implies a <italic>Yukawa-squared</italic> correction to the metric, yielding a closed-form deformation of the Schwarzschild/Reissner-Nordstr&#246;m lapse proportional to <math altimg='si18.svg'><mrow><mrow><mo>(</mo><mn>1</mn><mo linebreak='badbreak'>+</mo><msub><mi>m</mi><mi>X</mi></msub><mi>r</mi><mo>)</mo></mrow><mspace width='0.16em' /><msup><mi>e</mi><mrow><mo>&#8722;</mo><mn>2</mn><msub><mi>m</mi><mi>X</mi></msub><mi>r</mi></mrow></msup><mo linebreak='goodbreak'>/</mo><msup><mi>r</mi><mn>2</mn></msup></mrow></math> at leading order in the dark-sector backreaction. From this geometry we obtain compact analytic expressions for horizon quantities and curvature diagnostics, and we compute first-order shifts of the photon-sphere radius and shadow size. The resulting fractional corrections are controlled by a small dimensionless backreaction parameter and are exponentially suppressed for <math altimg='si19.svg'><mrow><msub><mi>m</mi><mi>X</mi></msub><mi>M</mi><mo>&#8819;</mo><mi mathvariant='script'>O</mi><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></mrow></math>. In the kinetically mixed theory, after diagonalizing the kinetic terms we show that the asymptotic exterior is fixed by the Gauss-law charge of the massless (Maxwell) combination, while any massive-mode contribution is necessarily short-ranged and Yukawa suppressed unless a conserved hidden charge is present. We further emphasize that magnetic-dipole/Breit operators are intrinsically angle dependent and do not generate isotropic exterior modifications for an unpolarized spherically symmetric configuration at leading order. Overall, our results provide a minimal, self-consistent analytic framework for how a massive hidden vector can induce short-ranged deformations of Schwarzschild/RN observables relevant to horizon-scale imaging and precision strong-field tests.

Ali Övgün

Philippines

Reggie C. Pantig

Black hole solutions in dark photon models

In this paper, we pursue an investigation of the consequences of a mixing between supersymmetric partners - the photon and photino - analogous to the so-called Primakoff effect, but induced by a Lorentz-symmetry violating (LSV) fermionic-condensate background. In our framework, the LSV parameters are introduced as members of a non-dynamical superfield. As a consequence, we show that naturally there appears a mixing term between the gauge boson and the gaugino, which can be readily seen in the superspace/superfield approach. We inspect the kinetic photon-photino mixing matrix in the scenario of stellar physics which we apply our results to. Bounds on the strength of the fermionic LSV background are can be set by invoking the energy loss argument and the solar data we adopt.

Bernard T. de Menezes

José A. Helayël-Neto

Stellar bounds on a model with photon-photino oscillation