arXiv subjects

Yong Song

Publications and source records attributed to Yong Song.

At least 19 recordsLinked to original sources

arXiv2026

Static spheres in black hole spacetimes: pairing, energy conditions, and an upper bound on the innermost radius

In this work, we investigate the existence, relation to the energy conditions, and radial bounds of static spheres in general static, spherically symmetric, asymptotically flat black hole spacetimes. By analyzing the global behavior of a radial function constructed from the mass and radial pressure functions, we prove that a static sphere necessarily requires a negative radial pressure (tension). Furthermore, we show that non-degenerate static spheres must always appear in pairs: an inner unstable sphere and an outer stable one. Assuming the Weak Energy Condition (WEC) always holds, the inner static sphere is characterized by a violation of the strong energy condition (SEC) inequality $\rho+p+2p_T<0$, where $\rho$, $p$, and $p_T$ denote the energy density, radial pressure, and tangential pressure, respectively; the SEC inequality is restored ($\rho+p+2p_T> 0$) at the outer sphere; the degenerate marginal case satisfies $\rho+p+2p_T=0$. In addition, focusing on the innermost static sphere and assuming that the WEC holds while the SEC is uniformly violated between the event horizon and this sphere, we derive a rigorous upper bound on its radius, \[ r^-_{\mathrm{sp}}\le \left[r_H^3+\frac{3r_H\bigl(1-8\pi r^2_H\rho(r_H)\bigr)}{8\pi\kappa}\right]^{1/3}, \] where $r_H$ is the horizon radius, $\rho(r_H)$ the energy density at the horizon, and $\kappa$ characterizes the strength of the SEC violation. These results establish a direct, analytic link between the energy conditions and the existence of static spheres, and provide a quantitative constraint on the matter environment of black holes possessing such orbits. The findings have potential applications in testing black hole solutions in general relativity and modified theories of gravity, as well as in interpreting related astronomical observations.

gr-qc↗

arXiv2026

Bounds on the radius of outermost photon sphere and black hole shadow in $n$-dimensional Einstein gravity

The photon sphere, which determines the contour of the black hole shadow, provides a direct probe of strong-field gravity. In this work, we derive model-independent bounds on both the outermost photon sphere radius $r_{\gamma,\mathrm{out}}$ and the shadow radius $r_{\mathrm{sh}}$ for static, spherically symmetric, asymptotically flat black holes in $n$-dimensional ($n\ge 4$) Einstein gravity, supported by an anisotropic matter field. We first establish a rigorous upper bound on $r_{\gamma,\mathrm{out}}$ under the Weak Energy Condition (WEC), the Strong Energy Condition (SEC), and an asymptotic decay condition on the matter fields, proving $r_{\gamma,\mathrm{out}} \le \bigl[(n-1)M\bigr]^{\frac{1}{n-3}}$, where $M$ is the ADM mass, with the bound saturated by the vacuum Schwarzschild-Tangherlini black hole. We further discuss the lower bound on $r_{\gamma,\mathrm{out}}$, clarifying that a conditional bound can be obtained from the innermost photon sphere under an extra monotonicity assumption. Turning to the black hole shadow, we derive both upper and lower bounds on $r_{\mathrm{sh}}$. Making use of the photon sphere upper bound and the fact that, under the WEC and SEC, the effective potential for null geodesics outside the outermost photon sphere is bounded below by that of the vacuum solution with the same ADM mass, we obtain $r_{\mathrm{sh}}\le\sqrt{\frac{n-1}{n-3}}\,\bigl[(n-1)M\bigr]^{\frac{1}{n-3}}$, while for the lower bound, using only the WEC, we prove $r_{\mathrm{sh}} \ge \left( \frac{n-1}{2} \right)^{\frac{1}{n-3}} \sqrt{\frac{n-1}{n-3}}r_H$, where $r_H$ is the horizon radius. Our results provide clear geometric constraints on the observable signatures of higher-dimensional black holes and underline the special role of the shadow as a robust observable.

gr-qc↗

arXiv2026

Diffusion Reinforcement Learning Based Online 3D Bin Packing Spatial Strategy Optimization

The online 3D bin packing problem is important in logistics, warehousing and intelligent manufacturing, with solutions shifting to deep reinforcement learning (DRL) which faces challenges like low sample efficiency. This paper proposes a diffusion reinforcement learning-based algorithm, using a Markov decision chain for packing modeling, height map-based state representation and a diffusion model-based actor network. Experiments show it significantly improves the average number of packed items compared to state-of-the-art DRL methods, with excellent application potential in complex online scenarios.

cs.RO↗

arXiv2026

A universal lower bound on the photon sphere radius in higher-dimensional black holes

The photon sphere, a hypersurface of circular null geodesics, plays a fundamental role in characterizing black hole spacetimes, influencing phenomena such as black hole shadows, gravitational lensing, and quasinormal modes. While universal upper bounds on the photon sphere radius have been established for both four-dimensional and higher-dimensional black holes, the question of a corresponding lower bound in higher-dimensional black holes remains less explored. In this work, we derive a universal lower bound for the photon sphere radius in static, spherically symmetric, asymptotically flat black hole spacetimes of arbitrary dimension $n\ge 4$. Under the assumptions of the weak energy condition, a non-positive trace of the energy-momentum tensor, and a monotonicity condition on the radial pressure function $|r^{n-1}p_r(r)|$, we prove that the photon sphere radius $r_\gamma$ satisfies $r_\gamma\ge (\frac{n-1}{2})^{1/(n-3)}r_H$, where $r_H$ is the radius of the outer event horizon. For $n=4$, this reduces to the known result $r_\gamma\ge \frac{3}{2}r_H$. Our result generalizes Hod's four-dimensional theorem to higher dimensions, and provides a new geometric constraint on the structure of black holes in extended theories of gravity.

gr-qc↗

arXiv2026

Bounds on the photon sphere radius for spherically symmetric black holes in n-dimensional Einstein gravity

The photon sphere, a hypersurface of null circular geodesics, plays a fundamental role in characterizing black hole spacetimes, influencing phenomena such as black hole shadows, gravitational lensing, and quasinormal modes. In this work, we derive both upper and lower bounds on the photon sphere radius for static, spherically symmetric, asymptotically flat black holes within $n$-dimensional Einstein gravity ($n\ge 4$), assuming an anisotropic matter field satisfying the weak energy condition and a non-positive trace of the energy-momentum tensor. For the upper bound, we obtain $r_\gamma\le [(n-1)M]^{\frac{1}{n-3}}$, where $M$ is the ADM mass. In the four-dimensional case ($n=4$), this reduces to $r_\gamma\le 3M$, in agreement with previous results. For the lower bound, under the additional assumption that $|r^{n-1}p_r(r)|$ is monotonically decreasing, we prove $r_\gamma\ge (\frac{n-1}{2})^{1/(n-3)}r_H$, where $r_H$ is the radius of the outer event horizon; for $n=4$ this gives $r_\gamma\ge \frac{3}{2}r_H$, also consistent with previous four-dimensional result. These results provide dimension-dependent geometric constraints that generalize well-known four-dimensional bounds to a specific class of higher-dimensional black holes (described by a Tangherlini-type metric) and deepen our understanding of spacetime structure in higher-dimensional gravitational theories.

gr-qc↗

arXiv2025

Robust topological invariants of timelike circular orbits for spinning test particles in black hole spacetimes

The spin-curvature coupling in the Mathisson-Papapetrou-Dixon (MPD) formalism induces non-geodesic motion, shifting the orbital parameters of spinning test particles in black hole spacetimes. We investigate whether these quantitative shifts alter the qualitative, global structure of the orbit manifold. Using a topological approach, we study timelike circular orbits (TCOs) for spinning particles in static, spherically symmetric spacetimes. By constructing an auxiliary vector field, we compute the topological winding number $W$ in horizon-bounded regions of asymptotically flat, anti-de Sitter (AdS), and de Sitter (dS) backgrounds. We find that $W$ is robust against both the magnitude and direction of the particle's spin: between two horizons, $W = -1$, guaranteeing at least one unstable TCO; outside the outermost horizon in asymptotically flat and AdS spacetimes, $W = 0$, enforcing that TCOs must appear in stable-unstable pairs or be absent. This spin independence reveals that the fundamental orbital structure is a property of spacetime geometry itself, not of the particle's spin. We validate this with quantitative examples in Schwarzschild, Schwarzschild-AdS, and Schwarzschild-dS spacetimes, showing explicit spin-induced TCO shifts while confirming the invariant topology. This result provides a topological foundation for interpreting gravitational waveforms from extreme mass-ratio inspirals involving spinning secondaries.

gr-qc↗

arXiv2025

The existence and upper bound for stable photon spheres in static spherically symmetric black holes

In this work, we establish the existence conditions and a universal upper bound on the radius of stable photon spheres (SPS) outside the event horizons of static, spherically symmetric, asymptotically flat black holes surrounded by matter fields. We prove that stable photon spheres exist if the external matter satisfies specific conditions. Furthermore, under the additional assumption of a monotonically decreasing mass-radius ratio $m(r)/r^3$ outside the horizon, we derive a strict upper bound on the radius $r_{\mathrm{sps}}$ of any stable photon sphere: $r_{\mathrm{sps}}<6M$, where $M$ is the asymptotic mass of the black hole. This bound is independent of specific black hole solutions and broadly applies to hairy black holes and other configurations with external matter fields meeting the stated energy conditions. Our results resolve fundamental questions regarding the existence and spatial constraints on stable photon orbits, with implications for gravitational lensing, accretion disk dynamics (e.g., the Aschenbach effect), and black hole shadow observations.

gr-qc↗

arXiv2025

From quasi-local definitions to a dynamical potential: A unified framework for evolving circular orbits in dynamical spacetimes

The study of circular orbits is fundamental in gravitational physics, yet their definition in dynamical spacetimes remains challenging due to the lack of temporal symmetry. In this work, we establish a unified framework by commencing from the geometrically invariant quasi-local definition of a particle surface. We demonstrate that this definition naturally leads to a set of conditions that can be recast into the language of a coordinate-dependent dynamical potential. This potential serves as a practical computational tool for locating evolving circular orbits within a specific coordinate system. We rigorously prove the equivalence between the quasi-local and dynamical potential approaches in dynamical spherically symmetric spacetimes. The efficacy and self-consistency of the dynamical potential method are explicitly verified through its application to the Oppenheimer-Snyder dust collapse model, where it correctly reproduces the established evolution equations for null and timelike circular orbits. This work bridges the gap between abstract geometric definitions and concrete calculations, providing a robust and adaptable framework for analyzing orbital dynamics in time-dependent gravitational fields.

gr-qc↗

arXiv2025

A New Perspective of the Meese-Rogoff Puzzle: Application of Sparse Dynamic Shrinkage

We propose the Markov Switching Dynamic Shrinkage process (MSDSP), nesting the Dynamic Shrinkage Process (DSP) of Kowal et al. (2019). We revisit the Meese-Rogoff puzzle (Meese and Rogoff, 1983a,b, 1988) by applying the MSDSP to the economic models deemed inferior to the random walk model for exchange rate predictions. The flexibility of the MSDSP model captures the possibility of zero coefficients (sparsity), constant coefficient (dynamic shrinkage), as well as sudden and gradual parameter movements (structural change) in the time-varying parameter model setting. We also apply MSDSP in the context of Bayesian predictive synthesis (BPS) (McAlinn and West, 2019), where dynamic combination schemes exploit the information from the alternative economic models. Our analysis provide a new perspective to the Meese-Rogoff puzzle, illustrating that the economic models, enhanced with the parameter flexibility of the MSDSP, produce predictive distributions that are superior to the random walk model, even when stochastic volatility is considered.

econ.EM↗

arXiv2025

Upper bound on the radius of the innermost stable circular orbit of black holes

In this work, we investigate a universal upper bound on the radius of the innermost stable circular orbit (ISCOs) for massive particles in static, spherically symmetric, and asymptotically flat black hole spacetimes. By analyzing the spacetime metrics with external matter fields, we derive the characteristic equation for ISCO via the effective potential method. By imposing appropriate energy conditions for the matter fields, we rigorously demonstrate that the ISCO radius is bounded by $r_{\mathrm{ISCO}}\le 6M$, where $M$ is the total ADM mass of the black hole. The Schwarzschild black hole saturates this bound ($r_{\mathrm{ISCO}}=6M$), and the Reissner-Nordstr\"om black hole, supergravity black holes, fluid sphere models, which satisfy the imposed energy conditions, also obey $r_{\mathrm{ISCO}}\le 6M$. The universality of this upper limit provides a theoretical benchmark for observational astrophysics: deviations from $6M$ in accretion disk observations or gravitational wave signals could indicate the presence of exotic matter fields. This work highlights the interplay between black hole geometry and external matter fields, paving the way for future studies in compact object dynamics.

gr-qc↗

arXiv2025

A unified topological classification of circular orbits for charged particles in black hole spacetimes

The study of circular orbits offers profound insights into the structure of spacetime around black holes. While the topological properties of these orbits are well-established for neutral particles, the influence of electric charge-particularly for massless particles-remains a subject of exploration. In this work, we employ a topological current $\phi$-mapping approach to systematically investigate the circular orbits of charged test particles in static, spherically symmetric black hole spacetimes with flat, anti-de Sitter (AdS), and de Sitter (dS) asymptotics. We demonstrate that the particle's charge significantly alters the topological classification of both timelike and null circular orbits. A key finding is that for multi-horizon black holes, if a circular orbit with fixed angular momentum and charge exists between two neighboring horizons, there will always be at least one unstable null and one unstable timelike circular orbit. Outside the outermost horizon, the asymptotic behavior of spacetime and the specific charge ratio crucially determine the topological charge $W$, dictating the existence and stability of orbits. Our results, validated through Reissner-Nordstr\"om (RN), RN-AdS, and RN-dS examples, extend the topological orbit classification framework and provide a foundation for potential applications in environments where effective charge dynamics may be relevant, such as magnetized plasmas around black holes.

gr-qc↗

arXiv2025

Bayesian inference for dynamic spatial quantile models with interactive effects

With the rapid advancement of information technology and data collection systems, large-scale spatial panel data presents new methodological and computational challenges. This paper introduces a dynamic spatial panel quantile model that incorporates unobserved heterogeneity. The proposed model captures the dynamic structure of panel data, high-dimensional cross-sectional dependence, and allows for heterogeneous regression coefficients. To estimate the model, we propose a novel Bayesian Markov Chain Monte Carlo (MCMC) algorithm. Contributions to Bayesian computation include the development of quantile randomization, a new Gibbs sampler for structural parameters, and stabilization of the tail behavior of the inverse Gaussian random generator. We establish Bayesian consistency for the proposed estimation method as both the time and cross-sectional dimensions of the panel approach infinity. Monte Carlo simulations demonstrate the effectiveness of the method. Finally, we illustrate the applicability of the approach through a case study on the quantile co-movement structure of the gasoline market.

econ.EM↗

arXiv2023

The particle surface of spinning test particles

In this work, inspired by the definition of the photon surface given by Claudel, Virbhadra, and Ellis, we give an alternative quasi-local definition to study the circular orbits of single-pole particles. This definition does not only apply to photons but also to massive point particles. For the case of photons in spherically symmetric spacetime, it will give a photon surface equivalent to the result of Claudel, Virbhadra, and Ellis. Meanwhile, in general static and stationary spacetime, this definition can be regarded as a quasi-local form of the effective potential method. However, unlike the effective potential method which can not define the effective potential in dynamical spacetime, this definition can be applied to dynamical spacetime. Further, we generalize this definition directly to the case of pole-dipole particles. In static spherical symmetry spacetime, we verify the correctness of this generalization by comparing the results obtained by the effective potential method.

gr-qc↗

arXiv2023

AIGC Empowering Telecom Sector White Paper_chinese

In the global craze of GPT, people have deeply realized that AI, as a transformative technology and key force in economic and social development, will bring great leaps and breakthroughs to the global industry and profoundly influence the future world competition pattern. As the builder and operator of information and communication infrastructure, the telecom sector provides infrastructure support for the development of AI, and even takes the lead in the implementation of AI applications. How to enable the application of AIGC (GPT) and implement AIGC in the telecom sector are questions that telecom practitioners must ponder and answer. Through the study of GPT, a typical representative of AIGC, the authors have analyzed how GPT empowers the telecom sector in the form of scenarios, discussed the gap between the current GPT general model and telecom services, proposed for the first time a Telco Augmented Cognition capability system, provided answers to how to construct a telecom service GPT in the telecom sector, and carried out various practices. Our counterparts in the industry are expected to focus on collaborative innovation around telecom and AI, build an open and shared innovation ecosystem, promote the deep integration of AI and telecom sector, and accelerate the construction of next-generation information infrastructure, in an effort to facilitate the digital transformation of the economy and society.

cs.AI↗

arXiv2023

A Light Yield Enhancement Method Using Wavelength Shifter for the STCF EMC

Super Tau-Charm Facility (STCF) is a next-generation high luminosity electron-positron collider facility and is currently one of the major options for accelerator-based particle physics experiment in China. The crystal-based electromagnetic calorimeter (EMC) with undoped CsI is a major sub-system of the STCF spectrometer. To fulfill the increasing physics requirements on measurement precision and the suffering of radiation, improving the detected light yield is an important task of STCF EMC R&D. This paper studies a "wavelength shifting in propagation" scheme for STCF EMC using the nanostructured organosilicon luminophore (NOL). The studies are performed by both Monte Carlo simulation and experimental tests. The light yield is proved to be improved by a factor of 1.59 in the experiment. Meanwhile, a study of the NOL's radiation hardness is carried out to verify the reliability of the NOL. No obvious degradation in the performance is observed with the total ionization does up to 100 krad, far beyond the total radiation dose of STCF with ten years of operation.

physics.ins-det↗

arXiv2022

Quasi-local studies of the particle surfaces and their stability in general spacetimes

In this paper, enlightened by the definition of the photon surface given by Claudel, Virbhadra and Ellis, we give a quasi-local definition of the particle surface. From this definition, one can study the evolution of the circular orbits in general spacetime. Especially, we pointed out that this definition can be used to get the spherical circular orbits in stationary spacetimes which cannot be got by the definition of Claudel, Virbhadra and Ellis. Further, we give a condition to exclude the particle surface in spacetime without gravity. Simultaneously, we give a quasi-local definition of the stability of the particle surface in general spacetime. From this definition, one can get the evolution equation of the innermost stable circular orbit (ISCO) in general spacetime. To verify the correctness of these definitions, we studied the circular orbits in some special cases and the results are all consistent with the previous results.

gr-qc↗

arXiv2021

The evolutions of the innermost stable circular orbits in dynamical spacetimes

In this paper, we studied the evolutions of the innermost stable circular orbits (ISCOs) in dynamical spacetimes. At first, we reviewed the method to obtain the ISCO in Schwarzschild spacetime by varying its conserved orbital angular momentum. Then, we demonstrated this method is equivalent to the effective potential method in general static and stationary spacetimes. Unlike the effective potential method, which depends on the presence of the conserved orbital energy, this method requires the existence of conserved orbital angular momentum in spacetime. So it can be easily generalized to the dynamical spacetimes where there exists conserved orbital angular momentum. From this generalization, we studied the evolutions of the ISCOs in Vaidya spacetime, Vaidya-AdS spacetime and the slow rotation limit of Kerr-Vaidya spacetime. The results given by these examples are all reasonable and can be compared with the evolutions of the photon spheres in dynamical spacetime

gr-qc↗

arXiv2021

Quasi-local photon surfaces in general spherically symmetric spacetimes

Based on the geometry of the codimension-2 surface in a general spherically symmetric spacetime, we give a quasi-local definition of a photon sphere as well as a photon surface. This new definition is the generalization of the one by Claudel, Virbhadra, and Ellis but without reference to any umbilical hypersurface in the spacetime. The new definition effectively rules out the photon surface which has noting to do with gravity. The application of the definition to the Lemaitre-Tolman-Bondi (LTB) model of gravitational collapse reduces to a problem of a second order differential equation. We find that the energy balance on the boundary of the dust ball can provide one appropriate boundary condition to this equation. Based on this key investigation, we find an analytic photon surface solution in the Oppenheimer-Snyder (OS) model and reasonable numerical solutions for the marginally bounded collapse in the LTB model. Interestingly, in the OS model, we find that the time difference between the occurrence of the photon surface and the event horizon is mainly determined by the total mass of the system but not the size or the strength of gravitational field of the system.

gr-qc↗