arXiv subjects

Zhong-Ying Fan

Publications and source records attributed to Zhong-Ying Fan.

At least 19 recordsLinked to original sources

arXiv2026

Axial Obstructions to Rotating Bumblebee Vacuum Solutions

We establish two obstructions to globally regular rotating constant-norm vector vacua. At an axial fixed point of a regular nondegenerate bifurcate Killing horizon, horizon-boost and axial invariance force every smooth symmetry-inheriting one-form to vanish, contradicting a strictly nonzero constant norm. Independently, varying axial conicity produces an orthonormal curvature component diverging as the inverse proper distance and precludes a $C^2$ extension. Applied to a three-parameter Kerr--disformal family in Einstein--bumblebee gravity, these results reveal a nonsmooth bumblebee one-form, while direct calculation shows that the Kretschmann scalar diverges as the inverse square of the transverse proper distance to either open exterior axis. Even the distinguished nonextremal branch selected by nonpolar outer-horizon regularity is therefore an exact nonpolar rotating exterior solution, not a globally regular isolated black hole. Together, these field- and metric-level obstructions provide a two-pronged no-go framework for globally regular rotating constant-norm vector vacua.

gr-qc↗

arXiv2026

Emergent symmetry and thermodynamic crossovers for supercritical AdS black holes

Ising symmetry typically emerges in the critical domain between liquid-gas phases. Universality of this property imposes strong constraints on the behavior of thermodynamic crossovers for supercritical fluids. In this work, we develop a novel approach to investigate the crossover lines for supercritical AdS black holes using Lee-Yang phase transition theory. We analytically continue Lee-Yang zeros into the complex plane within the supercritical region by keeping a modular pressure real. Consequently, we obtain a pair of complex crossover lines, which exhibit universal scalings and manifest the emergent Ising symmetry in the complex phase space. The real crossover lines are defined by projecting the complex crossovers onto the real phase space. As a result, the phase diagram above the critical point is divided into three distinct regimes: liquid-like, indistinguishable and gas-like states, in sharp contrast to scenarios featuring only a single crossover line.

cond-mat.stat-mech↗

arXiv2025

Probing the Penrose Process: Images of Split Hotspots and Their Observational Signatures

While theoretically established for decades, the Penrose process - energy extraction from rotating black holes - still lacks clear observational evidence. A promising theoretical framework posits magnetic reconnection in the ergosphere as a trigger, causing a plasmoid to separate into an escaping positive-energy fragment and an infalling negative-energy one. In this work, we investigate the observational imprints of this scenario. We treat the energized plasmoid as a hotspot and calculate its light curves for a realistic plasma magnetization. In particular, we further compare with the scenario in which the plasmoid, after fragmentation, falls into the black hole with positive energy, while all other conditions remain unchanged. Our results reveal that the process of fragmentation generates distinct flares, whose characteristics depend heavily on whether the infalling fragment carries negative or positive energy. We propose that these differences serve as identifiable signatures of the Penrose process.

astro-ph.HE↗

arXiv2025

Emergent Ising symmetry and supercritical fluids

The symmetry of Ising model questions any single crossover scenario for supercritical fluids. In this work, we firstly study a pair of thermodynamic crossovers $L^\pm$ analytically for the Van der Waals class fluids. We uncover an emergent $Z_2$ symmetry in addition to the universal scalings in the scaling regime for this class fluids. By using the self-reciprocal property between coexistenct phases, we further establish that under suitable conditions, the Ising symmetry generally emerges in the scaling regime for a general universality class. As a consequence, the thermodynamic crossovers $L^\pm$ generally exhibit an emergent $Z_2$ symmetry in the scaling regime. This partly resolves the symmetry puzzle raised by the Ising model. The results also imply that the physical importance of the Ising model in critical phenomenon is far beyond the scope of magentic transitions.

cond-mat.stat-mech↗

arXiv2025

Analytical approach to criticality of AdS black holes

We establish a hidden symmetry between the specific volumes of the coexistent phases and hence develop an analytical approach to study criticality of AdS black holes. In particular, using the method, we solve the coexistence line exactly for a variety of black holes, including the charged AdS black hole in diverse dimensions, the rotating AdS black hole, the Gauss-Bonnet black hole and the quantum BTZ black hole as well as the Van der Waals fluid.

gr-qc↗

arXiv2025

Critical phenomenon of quantum BTZ black holes

We extend the thermodynamics of quantum BTZ black holes by treating the quantum backreaction strength parameter $ν$ as a thermodynamic variable. We find various novel features. The critical point appears at $ν_c=1$ and a first order transition occurs either below the critical temperature for $ν<ν_c$ or above the critical temperature for $ν>ν_c$. By solving the coexistence curve analytically, we analyze the phase structures and clarify an unexpected discontinuity around the critical point. The critical exponents are significantly different from the mean field theory results and violate one of the scaling laws. We present an intepretation for this by using a universal three scale factor hypothesis for critical behavior of thermodynamic potential. Finally, we prove that given an arbitrarily small angular momenta, only one stable black hole phase can exist and hence no transition will occur.

hep-th↗

arXiv2024

Magnetic reconnection under centrifugal and gravitational electromotive forces

We examine the physical implications of the centrifugal and gravitational electromotive forces on magnetic reconnection in a Kerr black hole background. We find that both forces increase the reconnection rate, though the underlying mechanisms differ substantially. The gravitational force leads to a separation of charge density, breaking the quasi-neutrality of the plasma. In contrast, the centrifugal electromotive force affects the electric current by reducing the effective length of the current sheet. This reduction arises from the non-Euclidean spatial geometry observed by a locally comoving observer with respect to the rotating sheet. This phenomenon amplifies both the transport of charged carriers and the thermal-inertia effect within the current sheet, irrespective of the presence of a black hole.

astro-ph.HE↗

arXiv2024

Momentum-Krylov complexity correspondence

In this work, we relate the growth rate of Krylov complexity in the boundary to the radial momentum of an infalling particle in AdS geometry. We show that in general AdS black hole background, our proposal captures the universal behaviors of Krylov complexity at both initial and late times. Hence it can be generally considered as an approximate dual of the Krylov complexity at least in diverse dimensions. Remarkably, for BTZ black holes, our holographic Krylov complexity perfectly matches with that of CFT$_2$ at finite temperatures.

hep-th↗

arXiv2024

Fast magnetic reconnection in Kerr spacetime

We develop a relativistic scenario of fast magnetic reconnection process, for general magnetohydrodynamical plasmas around Kerr black holes. Generalizing the Petschek model, we study various properties of the reconnection layer in distinct configurations. When current sheet forms in the zero-angular-momentum (ZAMO) frame which corotates with the black hole, the reconnection rate for both radial and azimuthal configurations is decreased by spacetime curvature. However, when the current sheet forms in a non-ZAMO frame, which rotates either faster or slower than the black hole, detail analysis establishes that for any given slow rotations (subrelativistic at most) and mildly relativistic inflow, the ZAMO observer will find asymmetric reconnection rates for radial configuration: it is decreased on one side of the current sheet and is increased on the other side in comparison to the unrotation limit. This is valid to both the Sweet-Parker and the Petschek scenario. The results clarify the effects of rotation on the reconnection layer in the laboratory frame in the flat spacetime limit.

astro-ph.HE↗

arXiv2024

Criticality of global monopole charges in diverse dimensions

In this work, we construct charged AdS black holes with a global monopole charge in diverse dimensions and study the thermodynamics. We find a critical monopole charge below which the solution exhibits Van-der Waals like behaviors. In the context of holography, this could be intepreted using the boundary degrees of freedoms. As an example, we study the phase diagram in the four dimensions analytically. We further analyze the microstructures of the solution using Ruppeiner geometry. We find that repulsive interactions dominates for black holes in a wide range of temperatures. However, around the critical point, attractive interactions is dominant and the Ruppeiner scalar curvature shows universal behaviors: it has a critical exponent $2$ and coefficient $-1/8$ in diverse dimensions. Universality of the results is interpreted from the scaling behavior of free energy near the critical point for Van-der Waals like fluids.

hep-th↗

arXiv2024

Criticality of central charges for Gauss-Bonnet black holes

Employing extended phase space formalism, we study critical phenomenon of A-charge and C-charge for holographic theories dual to Gauss-Bonnet black holes. We find a universal critical Gauss-Bonnet coupling, giving rise to a universal ratio between the two central charges at the critical point. This leads to a new intepretation for critical behavior of Gauss-Bonnet black holes in terms of the boundary degrees of freedoms, although the solutions are electrically neutral. Another novel feature is for either of the central charges, the transition temperature is beyond the critical point but is upper bounded by causality of the boundary theories.

hep-th↗

arXiv2023

Generalised Krylov complexity

In this paper, we studied a set of generalised Krylov complexity for operator growth. We demonstrate their universal features at both initial times and long times using half-analytical technique as well as numerical results. In particular, by using the logarithmic relation to the Krylov entropy, we establish an inequality (\ref{master}) between the variance of the K-complexity and the generalised notions which holds in the long time limit. Extending the result to finite (but long) times, we show that for fast scramblers, the K-complexity constrains the growth of generalised complexity more stringently than the dispersion bound. However, for slow scramblers, the growth rate of K-complexity is tighter bounded by the generalised complexity in the other way around. Our results enlarge the zoo of Krylov quantities and may shed new light on the future research in this field.

hep-th↗

arXiv2023

Imaging a Semi-Analytical Jet model Generated by 3D GRMHD Simulation

Employing 3D GRMHD simulation, we study the images of a geometrically thin jet, whose emissions concentrate on its surface, for accretion system surrounding a central spinning BH. By introducing a strong magnetic field, we observe three phases of BH accretion evolution: (a) initially, both the accretion rate and the magnetic flux on the horizon gradually increase; (b) at an intermediate stage, the magnetic flux approximately reaches saturation, and a jet forms via the Blandford-Znajek (BZ) mechanism; (c) ultimately, the entire system achieves a dynamic equilibrium, and a magnetically arrested disk (MAD) forms. We carefully study the jet images during the saturation and MAD regimes at various frequencies and from different observational angles. We reveal the presence of U-shaped brighter lines near the jet surface boundaries, which can be attributed to the photons whose trajectories skim over the jet surface. The existence of these brighter lines is a unique feature of a geometrically thin jet. Moreover, we notice that the jet images are relatively insensitive to the observed frequencies of interest. Additionally, we observe that the time-averaged images for the highly oscillating MAD regime show only slight differences from those of the saturation regime.

astro-ph.HE↗

arXiv2023

Holographic fermions in asymptotically scaling geometries with hyperscaling violation

We investigate holographic fermions in general asymptotically scaling geometries with hyperscaling violation exponent $θ$, which is a natural generalization of fermions in Lifshitz spacetime. We prove that the retarded Green functions in this background satisfy the ARPES (angle-resolved photoemission spectroscopy) sum rules by introducing a dynamical source on a UV brane for zero density fermionic systems. The big difference from the Lifshitz case is that the mass of probe fermions decoupled from the UV theory and thus has no longer been restricted by unitarity bound. We also study finite density fermions at finite temperature, with dynamical exponent $z=2$. We find that the dispersion relation is linear but the logarithm of the spectral function is not linearly related to the logarithm of $k_\bot =k-k_F$, independent of charge $q$ and $θ$. Furthermore, we show that with the increasing of charge, new branches of Fermi surfaces emerge and tend to gathering together to form a shell-like structure when the charge reaches some critical value beyond which a wide band pattern appears in the momentum-charge plane. However, all sharp peaks will be smoothed out when $θ$ increases, no matter how much large the charge is.

hep-th↗

arXiv2022

Topological interpretation for phase transitions of black holes

In this work, we develop a universal picture from topology in the thermodynamic parameters space to describe first order phase transitions of black holes. By employing an off-shell internal energy, we find two types of topological defects. The first is normal, describing black holes which move with a nonzero velocity and acceleration, in a central force field. The second type of defects are exotic: they are static in the space, not describing black holes but encoding information about first order transitions. For each defect, we assign a winding number and an inertial mass. By studying neutral and charged black holes in asymptotically anti-de Sitter space, we show that first order transitions can be viewed as once or twice interchange of winding numbers between black holes and the exotic defects, through wired action at a distance. This corresponds to the usual notion: a smaller black hole grows into a larger black hole or vice versa. However, our topological analysis illustrates that the transition can also be locally interpreted as virtual collisions between black holes and the exotic defects. In this interpretation, a smaller black hole first grows into a new exotic defect whereas an original exotic defect grows into a larger black hole. All the defects simply change their positions and momentums, rather than interchanging the winding numbers. Critical point of the transition can be extracted when all the defects meet in the parameters space. Certain quantities, such as the Jacobians and the velocities of normal defects show universal behaviors near the critical point.

gr-qc↗

arXiv2022

The growth of operator entropy in operator growth

We study upper bounds on the growth of operator entropy $S_K$ in operator growth. Using uncertainty relation, we first prove a dispersion bound on the growth rate $|\partial_t S_K|\leq 2b_1 ΔS_K$, where $b_1$ is the first Lanczos coefficient and $ΔS_K$ is the variance of $S_K$. However, for irreversible process, this bound generally turns out to be too loose at long times. We further find a tighter bound in the long time limit using a universal logarithmic relation between Krylov complexity and operator entropy. The new bound describes the long time behavior of operator entropy very well for physically interesting cases, such as chaotic systems and integrable models.

hep-th↗

arXiv2022

Universal relation for operator complexity

We study Krylov complexity $C_K$ and operator entropy $S_K$ in operator growth. We find that for a variety of systems, including chaotic ones and integrable theories, the two quantities always enjoy a logarithmic relation $S_K\sim \log{C_K}$ at long times, where dissipative behavior emerges in unitary evolution. Otherwise, the relation does not hold any longer. Universality of the relation is deeply connected to irreversibility of operator growth.

quant-ph↗

arXiv2021

On holographic braneworld cosmology

Recently, S. Antonini and B. Swingle builded a holographic model for braneworld cosmology by introducing an ``end-of-the-world" (ETW) brane moving in a charged black hole spactime. In this paper, we will show that a holographic description of braneworld cosmology is possible for a general black hole spacetime with a pure tension brane if one implements a mixed boundary condition on the ETW brane. As a simple example, we study AdS-Schwarzschild black holes and show that a sensible Euclidean braneworld solution is compatible with localization of gravity on the ETW brane.

hep-th↗