We investigate thermodynamics of a non-interacting quantum field in a static black hole background. The horizon divergences are regulated by the brick wall method, which consists of subjecting the quantum field to Dirichlet boundary conditions on a surface (the brick wall) just outside the horizon. Using heat kernel and Mellin transform methods, we derive high-temperature expansions for the free energy and entropy and study the boundary and higher-order geometric effects on the horizon divergences induced by the brick wall. We consider real scalar, complex scalar, and Dirac fields in Schwarzschild, Reissner–Nordström and dilatonic black hole backgrounds, as well as in their near-horizon geometries. By evaluating the high-temperature expansion of the entropy (up to a certain order) at the Hawking temperature, we show that, for a given field type, the leading horizon divergence is the same for all the metrics considered. Moreover, we show that the different orders in the high-temperature expansion become comparable at the Hawking temperature and compare our findings with existing results in the literature. We derive an explicit formula for the sub-leading horizon divergence expressed in terms of the field mass, surface gravity, horizon area, and dilaton parameter, which is applicable to all the exact metrics considered. We also consider the possibility of using Neumann boundary conditions to regularize the horizon divergences.

Türkiye

Emine Ertuğrul

Birses Debir

Levent Akant

Boundary effects on the thermodynamics of quantum fields near a static black hole

In this work I study the finite temperature Casimir effect caused by a complex and massive scalar field that breaks Lorentz invariance in a CPT-even, aether-like manner. The Lorentz invariance breaking is caused by a constant space-like vector directly coupled to higher order field derivatives. This vector needs to be space-like in order to avoid non-causality problems that will arise with a time-like vector. I investigate the two scenarios of the scalar field satisfying either Dirichlet or mixed boundary conditions on a pair of flat parallel plates. I use the generalized zeta function technique that enables me to obtain the Helmholtz free energy and the Casimir pressure when the Casimir plates are in thermal equilibrium with a heat reservoir at finite temperature. I investigate two different directions of the unit vector, parallel and perpendicular to the plates. I examine both scenarios for both types of boundary conditions and, in both cases and for the two different boundary conditions, I obtain simple analytic expressions of the Casimir energy and pressure in the three asymptotic limits of small plate distance, high temperature, and large mass, examining all combinations of boundary conditions, unit vector direction, and asymptotic limits.

United States

Andrea Erdas

Finite temperature Casimir effect of a Lorentz-violating scalar with higher order derivatives

In this paper we present the first measurement of a Gallium Arsenide (GaAs) crystal as a scintillating calorimeter with dual heat and light readout within the DAREDEVIL project. The experimental setup features a 4.3 g GaAs ( GaAs-1) crystal, operated at approximately 10 mK coupled with a Neutron Transmutation Doped (NTD) thermal sensor for phonon detection and an auxiliary calorimeter for the detection of scintillation light. For the GaAs-1 crystal, a baseline resolution of 121 ± 2 eV has been achieved. While, with a 3.5 g GaAs (GaAs-2) crystal an even better baseline resolution of 44.5 ± 0.8 eV was achieved. Alpha and X-ray calibration sources were used to study the scintillation light response to different types of interacting radiation. The GaAs crystal exhibits a strong particle discrimination capability based on the emitted scintillation light, featuring a light yield (LY) of 0.9 ± 0.2 keV/MeV for $$\alpha $$ induced events and 0.07 ± 0.01 keV/MeV for $$\beta $$ / $$\gamma $$ events, both measured at 1 MeV. The unusual luminescence behavior, i.e. more light being produced under irradiation by $$\alpha $$ particles warrants further investigation, particularly due to its potential to enhance sensitivity to low-energy nuclear recoils from light dark matter scattering.

Italy

A. Melchiorre

D. Helis

A. Puiu

G. Benato

P. Carniti

I. Colantoni

A. Continenza

N. Marco

A. Ferella

C. Ferrari

F. Giannessi

C. Gotti

E. Monticone

S. Nagorny

France

E. Olivieri

L. Pagnanini

G. Pessina

C. Petrucci

S. Pirro

A. Prajapati

G. Profeta

M. Rajteri

P. Settembri

A. Shaikina

C. Tresca

D. Trotta

First measurement of GaAs as a scintillating calorimeter: achievements and prospects

Within the Bethe–Salpeter framework, we present a computation of space-like electromagnetic form factors for pseudoscalar mesons, including light and heavy-light systems. Our approach employs a flavour-dependent variation of the standard Taylor effective charge, which contains key contributions from the quark-gluon vertices. This effective interaction is a common ingredient of all relevant dynamical equations, and accommodates the crucial mass differences between the various quark flavours. Particular attention is paid to the nonperturbative determination of the quark-photon vertex. The computed electromagnetic form factors for the pion and the kaon mesons show excellent agreement with experimental determinations. In addition, the predictions for the charge radii of heavy-light systems are in overall good agreement with lattice QCD.

Spain

A. Miramontes

J. Papavassiliou

Germany

J. Pawlowski

Electromagnetic properties of heavy-light mesons

We derive and analyze a Schwarzschild-like Anti-de Sitter (AdS) (BH) obtained as a static, spherically symmetric solution of Einstein’s equations sourced by a cloud of strings (CoS) and a dark matter (DM) halo modeled by a Dehnen-type density profile. We first study the geodesic motion of massless and massive test particles, emphasizing how the CoS parameter $$\alpha $$ and the DM halo parameters $$(\rho _s,r_s)$$ influence photon spheres, circular orbits, the BH shadow, and the innermost stable circular orbit (ISCO). We then examine scalar perturbations via the effective potential and the associated quasinormal-mode (QNM) spectra, showing how $$\alpha $$ and $$(\rho _s,r_s)$$ deform oscillation frequencies and damping rates, thereby affecting stability diagnostics. Furthermore, we investigate the thermodynamics in the extended phase space, deriving the Hawking temperature, equation of state, Gibbs free energy, and specific heat capacity, and establishing a consistent first law and Smarr relation with natural work terms for $$\alpha $$ and $$(\rho _s,r_s).$$ We find that the interplay between the CoS and the DM halo produces quantitative and sometimes qualitative changes in both dynamical and thermodynamic properties, including shifts in the Hawking–Page transition and heat-capacity divergences, thereby reshaping the phase structure of Schwarzschild–AdS BHs.

India

Faizuddin Ahmed

Algeria

Abdelmalek Bouzenada

Brazil

Edilberto Silva

AdS black hole solution with a dark matter halo surrounded by a cloud of strings

Kaniadakis holographic dark energy is a one-parameter extension of the standard HDE framework, in which the horizon entropy is reformulated using Kaniadakis entropy. At the cosmological level, it has been shown to give rise to modified Friedmann equations, leading to a richer phenomenology compared to $$\Lambda $$ CDM. In this work we test the Kanadiakis holography model against multiple late-time observational probes, including Type Ia supernovae from PantheonPlus and Union3, Cosmic Chronometer measurements of the Hubble parameter and Baryon Acoustic Oscillation from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2). Using a Bayesian inference approach with MCMC methods, we constrain the cosmological parameters of the model and evaluate its performance against $$\Lambda $$ CDM through the Akaike Information Criterion. We find that Kaniadakis holography can provide a better fit for some data combinations, although $$\Lambda $$ CDM remains slightly statistically favored overall. These results highlight Kaniadakis holography as a competitive alternative to the standard cosmological model, offering valuable insights into the role of generalized entropy in dark energy dynamics.

Giuseppe Luciano

South Africa

Chile

Andronikos Paliathanasis

Late-time cosmological constraints on Kaniadakis holographic dark energy

In the present work, we perform a combined analysis of the cross sections for $$e^+ e^- \rightarrow K^+ K^-$$ and $$e^+ e^- \rightarrow K_S^0 K_L^0$$ by including the interference between direct coupling process and resonance intermediate process. When setting the isospin factor as a free parameter, we can well reproduce the structures in the cross sections for $$e^+ e^- \rightarrow K^+ K^-$$ and $$e^+ e^- \rightarrow K_S^0 K_L^0,$$ however, the isospin factor deviates with the isospin symmetry conservation predicted value of one. By fixing the isospin factor to be one, we find the cross sections for $$e^+ e^-\rightarrow K^+ K^-$$ can be accurately fitted, while the same model parameters fail to adequately reproduce the observed cross section for the process $$e^+ e^- \rightarrow K_S^0 K_L^0,$$ which indicate that there should be contributions from other vector meson states, such as $$\rho (2150)$$ and $$\omega (2220).$$ The combined analysis with $$\phi (2170),$$ $$\omega (2220)$$ and $$\rho (2150)$$ indicate that the inclusion of $$\rho (2150)$$ can improve the descriptions of the cross sections for $$e^+ e^-\rightarrow K^+ K^-$$ and $$e^+ e^- \rightarrow K_S^0 K_L^0.$$

China

Dian-Yong Chen

Jing Liu

Yu Bai

Chun-Hua Liu

Wen-Biao Yan

Zhao-Xia Meng

A combined analysis of $\textit{Y}$(2240) in the $$e^+ e^- \rightarrow K^+ K^-$$ and $$e^+ e^- \rightarrow K_S^0 K_L^0$$ processes

In this paper, we have studied the consequences of some representative neutrino flavor-symmetry models for tri-resonant leptogenesis (which is realized by having three nearly degenerate right-handed neutrinos). To be specific, we have considered a neutrino flavor-symmetry model realizing the TM1 mixing and modular $$\textrm{A}_4$$ , $$\textrm{S}_4$$ and $$\textrm{A}_5$$ symmetry models that have a right-handed neutrino mass matrix $$M_{\textrm{R}}$$ as shown in Eq. (6) which gives three exactly degenerate right-handed neutrino masses and consequently prohibits the leptogenesis mechanism to work successfully. For these models, we study the scenario that the desired right-handed neutrino mass splittings for leptogenesis to work are generated from the renormalization-group running effects. In such a scenario, we explore the parameter space that allows for the reproduction of the observed baryon-antibaryon asymmetry of the Universe.

Zhi-Cheng Liu

Zhen-hua Zhao

Renormalization group running triggered tri-resonant leptogenesis within neutrino flavor-symmetry models

This work explores the universal classification of thermodynamic topology for charged static black holes within the $$z=3$$ Hor̆ava-Lifshitz gravity theory, considering both canonical and grand canonical ensembles. We introduce a new topological subclass, denoted as $$\ddot{W}^{1-}$$ . This finding expands the existing topological classification, going beyond the five previously defined classes and their respective subclasses. The $$\ddot{W}^{1-}$$ subclass presents a distinct and previously unobserved stability profile: In the low-temperature regime, an unstable small black hole appears in the phase space, whereas, while in the high temperature regime, two unstable small black holes exist together with a stable large black hole. Our study underscores the dependence of charged black hole stability on the selection of the ensemble. These results contribute to refining and expanding the topological framework in black hole thermodynamics, providing key perspectives on the underlying nature of black holes and gravity.

Hao Chen

Meng-Yao Zhang

Czechia

Azerbaijan

Hassan Hassanabadi

Qihong Huang

Zheng-Wen Long

Novel topological subclass in Hor̆ava–Lifshitz black holes

In the present study, we investigate the quasibound states and scalar cloud of relativistic charged scalar fields bound to a Kerr–Newman black hole. We present the exact eigensolutions of the governing Klein–Gordon equation with non-minimal coupling in the black hole background. By imposing boundary conditions on the quasibound states, we are able to find the exact complex quasibound state frequencies of the corresponding radial wave functions in terms of the confluent Heun polynomial. The quantization formula obtained here allows us to determine the exact resonance frequency of a charged scalar cloud, thereby revisiting and extending the earlier result derived through the asymptotic matching approach. Our analysis shows that a stationary configuration can exist only when the charge coupling satisfies $$qr_Q<0$$ . In this case, the scalar cloud remains stationary due to a flux balance: an outgoing flux from the Cauchy horizon compensates for the ingoing particle flux at the event horizon. This mechanism distinguishes scalar clouds from ordinary quasibound states, where such a compensating flux is absent.

Thailand

David Senjaya

Revisiting Kerr–Newman black hole’s charged scalar cloud: flux balance