arXiv subjects

Zi-Yuan Li

Publications and source records attributed to Zi-Yuan Li.

9 recordsLinked to original sources

arXiv2026

Gaussian curvature and Lyapunov exponent as probes of black hole phase transitions

First-order phase transitions of black holes have been extensively studied within thermodynamic frameworks, yet the corresponding evolution of spacetime geometric properties remains unclear. This paper establishes a purely differential geometric framework to probe such phase transitions by analyzing the curvature of unstable null orbits. Using the geodesic curvature of the null circular orbit in the optical metric to locate the light ring, we demonstrate that the corresponding Gaussian curvature $K$ serves as a direct geometric signature of the phase transition. During a first-order phase transition, the curve $K$ versus temperature $T$ exhibits a multivalued structure within the spinodal region, precisely mirroring the swallowtail behavior of the free energy. Numerical analysis of Hayward-Letelier-AdS black holes confirms the effectiveness of this geometric signature. Our work demonstrates that the intrinsic geometric quantities of spacetime encode the information of black hole phase transitions. These quantities serve as geometric probes of black hole phase transitions, while their discontinuity between the small and large black hole branches exhibits order parameter-like behavior. As an extension of this geometric probe, we also find that the Gaussian curvature exhibits a heat-capacity-like divergence at the second-order phase transition point. These results provide a purely geometric foundation for understanding the correspondence between thermodynamics and spacetime curvature in the null case.

gr-qc↗

arXiv2026

Nonlinear topological laser based on multipole insulators

Two-dimensional higher-order topological insulators (HOTIs), characterized by distinctive one-dimensional edge states and zero-dimensional corner states, provide an ideal platform for developing higher-order topological lasers. In this work, we systematically investigate the two-dimensional Benalcazar-Bernevig-Hughes (BBH) model, which hosts quantized quadrupole moments and topologically protected corner and edge states. By confining the lasing mode to selected topological corner or edge states under controlled gain, we demonstrate that the stable light excitation achieved after long-time evolution is predominantly determined by the topological properties of the model Hamiltonian. To characterize the system's topological features, we introduce several diagnostic ratios: the corner decay ratio $τ_{1}$ and edge-to-corner ratio $τ_{2}$ quantify the localization degree and spatial extent of corner states, respectively, while the inter-corner transfer ratio $χ$ measures the intensity transfer efficiency mediated by coherent edge-state dynamics. The abrupt changes in $τ_{1}$ and $τ_{2}$ as functions of the hopping parameter $γ/λ$ directly reveal topological phase transitions, providing a comprehensive toolkit for extracting topological signatures from the system's dynamical evolution. Additionally, modulating the lattice site parity enables flexible tuning of corner state localization positions, offering insights for device engineering. Our calculations reveal that achieving bistability between corner states and edge states is relatively challenging.

cond-mat.str-el↗

arXiv2026

Universal geometric framework for black hole phase transitions: from multivaluedness to classification

Recent studies have revealed synchronized multivalued behavior in thermodynamic, dynamical, and geometric quantities during the black hole first-order phase transition, which enables a diagnosis from different perspectives, yet its fundamental origin has remained poorly understood. By constructing a unified geometric framework integrating real analysis and covering space theory, we reveal the universal mathematical mechanism behind this phenomenon. We prove that this multivaluedness originates from two non-degenerate critical points in the temperature function $T(r_+)$, where $r_+$ is the horizon radius, which fold the parameter space into a three-sheeted covering structure. As a direct application, we propose that a black hole undergoes a first-order phase transition if and only if its $T(r_+)$ curve has two extrema. Accordingly, we establish a classification scheme, denoted $A1$, $A2$, and $B$ for black holes. This scheme offers a complementary perspective to classifications based on global topological invariants. Our work provides a theoretical foundation for diagnosing phase transitions via multivaluedness and establishes a unified geometric perspective on black hole thermodynamics, chaotic dynamics, and spacetime structure during first-order phase transitions.

gr-qc↗

arXiv2026

Geometric unification of timelike orbital chaos and phase transitions in black holes

The deep connection between black hole thermodynamics and spacetime geometry remains a central focus of general relativity. While recent studies have revealed a precise correspondence for null orbits, given by $K = -λ^2$ between the Gaussian curvature $K$ and the Lyapunov exponent $λ$, its validity for timelike orbits had remained unknown. Our work introduces the massive particle surface (MPS) framework and constructs a new geometric quantity $\mathcal{G}$. We demonstrate that $\mathcal{G} \propto -λ^2$ on unstable timelike orbits, thus establishing the geometry-dynamics correspondence for massive particles. Crucially, near the first-order phase transition of a black hole, $\mathcal{G}$ displays synchronized multivalued behavior with the Lyapunov exponent $λ$ and yields a critical exponent $δ=1.0244$. Our results demonstrate that spacetime geometry encodes thermodynamic information, opening a new pathway for studying black hole phase transitions from a geometric perspective.

gr-qc↗

arXiv2022

High-order harmonic generations in tilted Weyl semimetals

We investigate high-order harmonic generations (HHGs) under the comparison of Weyl cones in two types. Due to the hyperboloidal electron pocket structure, strong noncentrosymmetrical generations in high orders are observed around a single type-II Weyl point, especially at frequency zero. Such remarkable DC signal is proved to have attributions from the intraband transition after spectral decomposition. Under weak pulse electric field , the linear optical response of a non-tilted Weyl cone is consistent with the Kubo theory. With more numerical simulations, we conclude the non-zero chemical potential can enhance the even-order generations, from the slightly tilted system to the over-tilted systems. In consideration of dynamical symmetries, type-I and -II Weyl cones also show different selective responses under the circularly polarized light. Finally, using a more realistic model containing two pairs of Weyl points, we demonstrate the paired Weyl points with opposite chirality could suppress the overall even-order generations.

cond-mat.mes-hall↗

arXiv2022

Improving the machine learning based vertex reconstruction for large liquid scintillator detectors with multiple types of PMTs

Precise vertex reconstruction is essential for large liquid scintillator detectors. A novel method based on machine learning has been successfully developed to reconstruct the event vertex in JUNO previously. In this paper, the performance of machine learning based vertex reconstruction is further improved by optimizing the input images of the neural networks. By separating the information of different types of PMTs as well as adding the information of the second hit of PMTs, the vertex resolution is improved by about 9.4 % at 1 MeV and 9.8 % at 11 MeV, respectively.

physics.ins-det↗

arXiv2021

A method for sharing dynamic geometry information in studies on liquid-based detectors

The liquid-based detectors are widely used in particle and nuclear physics experiments. Due to the fixed way of constructing geometry in detector simulation such as Geant4, it is usually difficult to describe the non-uniformity of liquid in detectors. We propose a method based on GDML and tessellated detector description to share the detector geometry information between Computational Fluid Dynamics (CFD) simulation software and detector simulation software. The method makes it possible to study the impact of liquid flow and non-uniformity on some key performance of the liquid-based detectors, such as event vertex reconstruction resolution. It will also be helpful in detector design and performance optimization.

physics.ins-det↗

arXiv2017

Antiproton identification below threshold with AMS-02 RICH detector

The Alpha Magnetic Spectrometer (AMS-02) was installed on the International Space Station (ISS) and it has been collecting data successfully since May 2011. The main goals of AMS-02 are the search for cosmic anti-matter, dark matter and the precise measurement of the relative abundance of elements and isotopes in galactic cosmic rays. In order to identify particle properties, AMS-02 includes several specialized sub-detectors. Among them, the AMS-02 Ring Imaging Cherenkov detector (RICH) is designed to provide a very precise measurement of the velocity and electric charge of particles. We describe a method to reject the dominant electron background in antiproton identification with the use of the AMS-02 RICH detector as a veto for rigidities below 3 GV. Ray tracing integration method is used to maximize the statistics of $\bar{p}$ with the lowest possible $e^{-}$ background, providing 4 times rejection power gain for $e^{-}$ background with respect to only 3\% of $\bar{p}$ signal efficiency loss. By using the collected cosmic-rays data, $e^{-}$ contamination can be well suppressed within 3\% with $β\approx 1$, while keeping 76\% efficiency for $\bar{p}$ below the threshold.

physics.ins-det↗

arXiv2016

GOE statistics in graphene billiards with the shape of classically integrable billiards

A crucial result in quantum chaos, which has been established for a long time, is that the spectral properties of classically integrable systems generically are described by Poisson statistics whereas those of time-reversal symmetric, classically chaotic systems coincide with those of random matrices from the Gaussian orthogonal ensemble (GOE). Does this result hold for two-dimensional Dirac material systems? To address this fundamen- tal question, we investigate the spectral properties in a representative class of graphene billiards with shapes of classically integrable circular-sector billiards. Naively one may expect to observe Poisson statistics, which is indeed true for energies close to the band edges where the quasiparticle obeys the Schrödinger equation. However, for energies near the Dirac point, where the quasiparticles behave like massless Dirac fermions, Pois- son statistics is extremely rare in the sense that it emerges only under quite strict symmetry constraints on the straight boundary parts of the sector. An arbitrarily small amount of imperfection of the boundary results in GOE statistics. This implies that, for circular sector confinements with arbitrary angle, the spectral properties will generically be GOE. These results are corroborated by extensive numerical computation. Furthermore, we provide a physical understanding for our results.

quant-ph↗