In the Kerr–Sen black hole, this study investigates the changes in hotspot images before and after the occurrence of magnetic reconnection. After reviewing the Comisso–Asenjo magnetic reconnection process and introducing the hotspot imaging method, we examine the temporal evolution of hotspot intensity, including when energy extraction occurs, when it does not occur, and when the observer’s azimuthal angle is altered. We also discuss the influence of the black hole’s expansion parameter and spin on hotspot imaging. The results indicate that the first flare may serve as a potential signature of ongoing energy extraction; changing the observer’s azimuthal angle may alter the time interval between the first and second flares; a larger expansion parameter makes it more difficult to identify the energy extraction signal, and a higher spin also makes it more challenging to detect the energy extraction signal.

China

Ke Wang

Xiao-Xiong Zeng

Hotspot images driven by magnetic reconnection in Kerr–Sen black hole

We investigate the potential of extreme mass-ratio inspirals to constrain quantum Oppenheimer–Snyder black holes within the framework of loop quantum gravity. We consider a stellar-mass object orbiting a supermassive Oppenheimer–Snyder black hole in an equatorial eccentric trajectory. To explore the dynamical behavior of the system, we analyze its orbital evolution under gravitational radiation within the adiabatic approximation and the mass-quadrupole formula for different initial orbital configurations. Our results show that the quantum correction parameter $$\hat{\alpha }$$ slows down the evolution of the orbital semi-latus rectum and eccentricity. We then employ the numerical kludge method to generate the corresponding time-domain gravitational waveforms. To assess detectability, we include Doppler modulation due to the motion of space-based detectors and compute the frequency-domain characteristic strain. By evaluating mismatches between response signals for different values of $$\hat{\alpha }$$ , we show that even small corrections $$( \hat{\alpha } \sim 10^{-5})$$ produce distinguishable effects. Our analysis suggests that future space-based detectors such as LISA can probe quantum gravitational corrections in the strong-field regime and place constraints significantly stronger than those from black hole shadow observations.

Sen Yang

Yu-Peng Zhang

Li Zhao

Yu-Xiao Liu

Constraints on quantum Oppenheimer–Snyder black holes with eccentric extreme mass-ratio inspirals

The Georgi–Machacek (GM) model extends the Higgs sector of the Standard Model by introducing additional triplets, preserving custodial symmetry at tree level and allowing large triplet vacuum expectation values (VEVs) of order $$\mathcal {O}(10)$$ GeV. Theoretical constraints on the model’s parameters include bounded-from-below (BFB) conditions for the tree-level scalar potential. This study goes beyond the BFB constraints by examining the positive definiteness of the effective potential in the GM model to ensure the absence of deeper vacua in regions with large field values. Using a one-loop renormalization group-improved (RG-improved) effective potential and new criteria for positive definiteness of homogeneous polynomials with multiple variables (necessary due to custodial symmetry breaking effects from loops), we numerically analyze these constraints. Our results reveal that the parameter ranges allowed by positive definiteness differ significantly from those derived from tree-level BFB conditions. Notably, some regions previously excluded by tree-level BFB constraints remain viable under the one-loop RG-improved scalar potential. Besides, certain parameter spaces that satisfy tree-level BFB constraints with electroweak (EW) scale couplings should be excluded due to violations of positive definiteness in large field-value regions. Our numerical analysis, based on the new criteria for positive definiteness of homogeneous polynomials with multiple variables, not only revises the GM model’s viability map but also provides a methodological template for stability studies in other extended Higgs models.

Xiaokang Du

Fei Wang

Positive definiteness constraints of effective scalar potential in Georgi–Machacek model

Thailand

David Senjaya

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

In this paper we study the shadow and quasi-normal modes (QNMs) of a black hole (BH) surrounded by a dark matter halo with Hernquist-type density distribution, which was reported in Cardoso et al. (Phys. Rev. D 105(6):L061501, 2022). In astrophysical scenarios, we find that the shadow radius enlarges as the compactness of halo increases. Therefore, we obtain an upper bound for the compactness $$\mathcal{C}\le 0.092$$ with the Event Horizon Telescope (EHT) observations. We calculate axial gravitational QNMs of the galactic BH up to $$\mathcal{C}\sim \mathcal{O}(1)$$ , and fit the redshift relative to Schwarzschild QNMs up to second order in the compactness (for $$\mathcal{C}\le 0.3)$$ . These highly redshifted QNMs, resulting from large compactness, are key to modeling the dark matter halo.

Xing-Hui Feng

Guang-Yu Zhang

Shadow and quasi-normal modes of Schwarzschild–Hernquist black hole

A quantum-corrected black hole model arising from gravitational collapse in the framework of asymptotically safe gravity was recently proposed in Bonanno et al. (Phys Rev Lett 132:031401, 2024). Quantum corrected spacetime strongly deviates from the Schwarzschild solution near the event horizon, quickly merging with the Schwarzschild metric in the far region. While quasinormal modes and gray-body factors have been analyzed for test fields in this background, no such analysis has yet been performed for gravitational perturbations. In this work, we study axial gravitational perturbations of these black holes by modeling the effective quantum corrections through an anisotropic fluid energy-momentum tensor. We compute both quasinormal modes and gray-body factors, and show that quantum corrections enhance the quality factor of the oscillations, thereby making the quantum-corrected black hole a more efficient gravitational wave emitter. At asymptotically late times, the power-law decay is indistinguishable from Price’s tails, which behave as $$ \sim t^{-(2\ell + 3)} $$ , where $$ \ell $$ is the multipole number. We also demonstrate that quantum corrections lead to a suppression of the gray-body factors and examine the validity of the correspondence between gray-body factors and quasinormal modes.

Czechia

B. Lütfüoğlu

Quasinormal modes and gray-body factors for gravitational perturbations in asymptotically safe gravity

Erratum to: Black hole in Dehnen $$\left( 1,4,\frac{1}{2}\right) $$ dark matter halo: exact solution, lensing, light ring, and thermodynamics

Motivated by the recent observation of the open-charm tetraquark $$T_{c\bar{s}0}^{a}(2327)$$ by the LHCb Collaboration, as well as results from Lattice QCD calculations, we consider the $$T_{c\bar{s}0}^{a}(2327)$$ and the $$D_{s0}^{*}(2317)$$ as $\textit{DK}$ molecular states, with $$I(J^{P})$$ equal to $$1(0^{+})$$ and $$0(0^{+})$$ , respectively, and we investigate their strong decay behavior in an effective Lagrangian approach. Within the model parameter range, we can reproduce the $$T_{c\bar{s}0}^{a}(2327)$$ experimental decay width, with the assumption that the $$D_{s}^{+}\pi ^{0}$$ is the dominant decay channel of the $$T_{c\bar{s}0}^{a+}(2327)$$ . In the same parameter range, we can establish a stringent limitation for the decay width of the $$D_{s0}^{*}(2317)$$ , which is $$(63.0-209)~\textrm{keV}$$ being significantly smaller than the PDG upper limit value.

Italy

Zi-Li Yue

Quan-Yun Guo

Dian-Yong Chen

Elena Santopinto

Determining the width of $$D_{s0}^{*}(2317)$$ by using $$T_{c\bar{s}0}^{a}(2327)$$ in a molecular frame

This paper studies the quantization of the future null infinity ( $$\mathscr {I}^+$$ ) of an asymptotically flat spacetime. Based on the observation by Ashtekar and Speziale that $$\mathscr {I}^+$$ can be regarded as an extremal weakly isolated horizon, we extend the quantization framework developed for weakly isolated horizon to quantize $$\mathscr {I}^+$$ . We first show that the symplectic structure of $$\mathscr {I}^+$$ is equivalent to the sum of the symplectic structures of two $\textit{SU}$(2) Chern–Simons theories with opposite levels. Based on this observation, we apply Chern–Simons quantization approach to quantize $$\mathscr {I}^+$$ . Finally, we compute the entropy of $$\mathscr {I}^+$$ by counting the microstates, showing that it is proportional to the area of $$\tilde{\Delta }$$ , a spacelike cross-section of $$\mathscr {I}^+$$ . Our result is consistent with the universal entropy formula in the framework of (weakly) isolated horizon.

Hongwei Tan

Kui Xiao

Shoucheng Wang

Null infinity as $\textit{SU}$(2) Chern–Simons theories and its quantization

Hawking’s Chronology Protection Conjecture (CPC) proposes that the laws of physics prevent the formation of time machine. In his original argument, fields near a would-be chronology horizon undergo repeated blueshifts, signaling the onset of instabilities. In this work, we obtain an exact analytical solution of the Klein–Gordon equation for a relativistic scalar field in a spherically symmetric Morris–Thorne traversable wormhole. By polynomializing the radial equation and analyzing the Klein–Gordon current, we find that the resulting radiation modes generically possess complex eigenfrequencies: unstable modes grow in time and propagate inward toward the throat, while stable modes decay and flow outward. This directional instability prevents stationary configuration required to support time machine constructions, providing a dynamical obstruction consistent with Hawking’s Chronology Protection Conjecture.

Probing the chronology protection conjecture via scalar quasiresonance