Regular black holes offer a compelling framework to explore the consequences of resolving the central singularity of standard black holes. Using the Simpson–Visser “black-bounce” geometry as an elegant, analytically tractable framework, we explore the intricate thermodynamic behavior in such models. We demonstrate that this regular spacetime exhibits a critical instability, marked by a phase transition where the heat capacity is discontinuous. This transition signals a fundamental change in the black hole’s evaporation state, which depends on the regularization parameter. Pushing beyond the semiclassical limit, we then derive the leading-order quantum corrections to the entropy via the Hamilton–Jacobi tunneling formalism. Our analysis provides a refined statistical basis for the entropy of non-singular spacetimes and offers a quantitative analysis of the nature of the black hole end-state. These results reveal that singularity resolution is not merely a geometric modification but a profound thermodynamic event, with direct implications for the stability and ultimate fate of evaporating black holes.

India

Vinayak Joshi

Ashok Joshi

Thermodynamic phase transitions and quantum entropy corrections in the Simpson–Visser regular black hole

We present version 1.11 of , which extends the software package in several major ways to improve the handling of efficiency tables, the computation of observables in different reference frames and the calculation of statistical limits and/or significance. We detail how these improvements, whose development was motivated by the desire to implement two Run 2 LHC analyses targeting signatures with soft leptons and missing energy and exhibiting mild excesses (ATLAS-SUSY-2018-16 and ATLAS-SUSY-2019-09), have been implemented by both direct extensions of the code and integrations with third-party software. We then document the implementation and validation of these analyses, demonstrating their utility along with the improved statistics capabilities of through an investigation of the Next-to-Minimal Supersymmetric Standard Model in the context of a larger set of overlapping excesses in channels with soft leptons/jets and missing transverse energy.

United States

United Kingdom

Jack Araz

France

Benjamin Fuks

Mark Goodsell

Taylor Murphy

Deciphering compressed electroweakino excesses with

We investigate the superradiant instability of Ayón-Beato–García–de Sitter (ABG-dS) black holes under charged scalar field perturbations, employing both time-domain evolutions and frequency-domain computations. We demonstrate that the instability manifests exclusively for the spherically symmetric mode with $$\ell =0$$ for both massless and massive scalar field perturbations. In contrast, asymptotically flat ABG black holes remain stable in the massless limit, a finding that highlights the crucial role of the cosmological horizon in providing a confining boundary. We further analyze the dependence of the instability growth rate on the cosmological constant $$\Lambda $$ , the black hole charge $\textit{Q}$, the scalar field charge $\textit{q}$, and the scalar field mass $$\mu $$ . We find that the growth rate peaks at intermediate values of $$\Lambda $$ and $\textit{q}$, and increases monotonically with $\textit{Q}$. Conversely, an increase in the scalar field mass $$\mu $$ suppresses the instability, eventually quenching it when $$\mu $$ is sufficiently large. Compared with Reissner–Nordström–de Sitter black holes, ABG-dS black holes exhibit distinct instability characteristics, which arise from the modified electrostatic potential induced by nonlinear electrodynamics.

China

Yizhi Zhan

Hengyu Xu

Haowei Chen

Shao-Jun Zhang

Charged superradiant instability of spherically symmetric regular black holes in de Sitter spacetime: time- and frequency-domain analysis

The Lee–Yang phase transition theory applied in the anti-de Sitter (AdS) black hole has inspired the exploration of complex phase diagram and supercritical phenomena in black hole thermodynamics. In this study, we extend the approach to the four dimensional Born–Infeld AdS black hole. This system exhibits a rich phase structure, including reentrant phase transitions, due to the modulation of the Born–Infeld nonlinear parameter. Through the Lee–Yang zeros, we obtained the complex phase diagram of the Born–Infeld AdS black hole and derived the supercritical crossover line – Widom line, which strictly originates from the first-order stable critical point. The results indicate that Born–Infeld nonlinear effects significantly alter the types and characteristics of phase transition in critical region, while do not disrupt the uniqueness of the Widom line in supercritical region. Our study uncovers a universal simplified feature of the thermodynamic behavior of nonlinear gravitational systems in supercritical region. It also deepens our understanding of the fundamental connection between critical phenomena and continuous phase transitions in the extended phase space of black holes.

Fei Guo

Zhen-Ming Xu

Complex plane phase diagram and Widom line for the Born–Infeld black holes with reentrant phase transition

This paper investigates the shadow images of rotating charged black holes in Kalb–Ramond (KR) gravity, using an accretion disk that is both optically and geometrically thin and located on the equatorial plane as the light source model. The results show that, compared to Sgr A*, the observational data of M87* impose stronger constraints on the charge parameter $\textit{Q}$ and the Lorentz-violating parameter $$\mathcal {G}$$ . Under the thin accretion disk model, a larger observer inclination $$\theta _o$$ deforms the central brightness depression into a hat-like structure. The parameters $$(a, Q, \mathcal {G})$$ mainly affect the size of the central brightness depression and the brightness of the critical curve, where increasing these parameters reduces the shadow size and enhances the distinguishability of the critical curve. In the retrograde accretion disk case, the crescent-shaped bright area appears on the side opposite to that in the prograde case. In addition, we compute the distribution of the redshift factor on the projection screen. The results indicate that the Doppler effect induced by large $$\theta _o$$ enhances the blueshift in the image, while the light emitted by particles plunging into the black hole leads to strong redshift near the central brightness depression. Finally, we study the polarization images under synchrotron radiation and find that the polarization intensity $$\mathcal {P}_o$$ reaches its maximum around the lensed image and higher-order images, whereas no polarization vectors appear within the central brightness depression. This stands in sharp contrast to horizonless compact objects. These findings contribute to a deeper understanding of the shadow properties of charged black holes within Lorentz-violating gravity.

Chen-Yu Yang

Ke-Jian He

Xiao-Xiong Zeng

Li-Fang Li

Observational signatures and polarized images of rotating charged black holes in Kalb–Ramond gravity

We investigate two simplified non-singular cyclic models with a negative time-varying cosmological constant to represent the non-conventional mechanism of negative cosmological constant expected to address the late-time cosmic acceleration. We show that a physically acceptable evolution with positive energy density can be realized, while negative energy density dominates in case of a positive or zero cosmological constant. In the first model, we demonstrate a sign flipping of the cosmic pressure in a quintessence-dominated universe with no violation of the null energy condition. In the second model, we propose a matter-bounce scenario with showing the crossing of the phantom divide line in the vicinity of the bounce. We find that while we get positive kinetic term and scalar potential, the sum of scalar and quantum potentials is negative.

Egypt

Nasr Ahmed

Japan

Kazuharu Bamba

Quintessence-dominated cyclic universe with negative cosmological constant

$$s\rightarrow u$$ weak decays of heavy flavor hadrons play a unique role in the field of heavy flavor physics. In this work, we investigate semileptonic $$s\rightarrow u$$ decays of singly heavy baryons in the light-front approach under the three-quark picture. Firstly, we provide all the form factors using this quark model, in particular for $$f_{3}$$ and $$g_{3}$$ , which are usually considered non-extractable in recent literature. We also discuss the heavy quark limit for the form factors, and some of our results differ from those in the literature. We find that, when considering the heavy quark limit, the $$m_{s}$$ correction may not be negligible. Secondly, we apply the obtained form factors to predict some observables in semileptonic decays. It is worth noting that, due to the extremely small phase space, lepton flavor universality (LFU) is sensitive to the masses of leptons, and precise measurement of LFU is expected to be an important tool for testing the standard model.

Yi-Peng Xing

Xiao-Qian Jiang

Zhen-Xing Zhao

Semileptonic $$s\rightarrow u$$ decays of singly heavy baryons

We analyze the Macdonald’s ($\textit{q}$, $\textit{t}$)-deformed hypergeometric functions with one and two set variables and present their constraints. We prove the uniqueness to the solutions of these constraints. We propose a concise method to prove the superintegrability relations for ($\textit{q}$, $\textit{t}$)-deformed matrix models, where the constraints of hypergeometric functions play a crucial role. A conjectured superintegrability relation in the literature for the refined Chern–Simons model can be easily proved by our method. Moreover, we construct a general ($\textit{q}$, $\textit{t}$)-deformed matrix model. We give the constraint conditions for parameters in the integral. The superintegrability relations for the ($\textit{q}$, $\textit{t}$)-deformed integrals with allowed parameters are derived from the hypergeometric constraints.

Fan Liu

Rui Wang

Jie Yang

Wei-Zhong Zhao

Superintegrability for some ($\textit{q}$, $\textit{t}$)-deformed matrix models

The first results for charged Higgs pair production associated with a neutral gauge boson at future multi-TeV muon colliders are presented within the framework of the Two-Higgs-Doublet Model (THDM). In this phenomenological study, we update the viable parameter space of the Type-X and Type-II THDM. All two-body decay channels of the charged Higgs boson are then evaluated with the help of . The dominant branching fractions of the charged Higgs decay modes are shown within the allowed parameter space of the considered models. The production cross sections also include initial-state radiation corrections up to two-loop order in this work. The signal significances for the production processes are then examined by scanning over the viable parameter space of the models. With the high integrated luminosity planned for future multi-TeV muon colliders, the production signals can be observed with a statistical significance exceeding $$5\sigma $$ for several selected points within the allowed parameter space.

Vietnam

Khiem Phan

Quang Pham

Charged Higgs pair production associated with neutral gauge bosons at future multi-TeV muon colliders

We investigate massive scalar perturbations and several characteristics of particle motion in the spacetime of regular black holes arising in four-dimensional quasi-topological gravity. Quasinormal modes are computed using high-order WKB approximations with Padé resummation and verified through time-domain integration. For moderate values of the scalar-field mass, the time-domain profiles confirm the WKB results with excellent accuracy. As the mass increases, the damping rate decreases substantially, indicating the approach to the quasi-resonant regime of long-lived modes. For sufficiently large masses, the late-time signal becomes dominated by oscillatory power-law tails, which mask the quasi-resonant mode in the time-domain profile. In addition, we analyze photon motion and circular geodesics, including the photon-sphere radius, shadow size, Lyapunov exponent, and ISCO characteristics. These quantities exhibit only moderate deviations from their Schwarzschild values, unlike the Hawking temperature of the black hole.

Czechia

Bekir Lütfüoğlu

Long-lived quasinormal modes, shadows and particle motion in four-dimensional quasi-topological gravity