arXiv subjects

Xin-Yu Wang

Publications and source records attributed to Xin-Yu Wang.

11 recordsLinked to original sources

arXiv2026

Equilibrium and nonequlibrium scaling behaviors of localization transition in a non-Hermitian Aubry-André model with onsite gain and loss

The interplay between non-Hermiticity and localization has attracted considerable interest, yet the driven dynamics of localization transitions in non-Hermitian systems with on-site gain and loss remains largely unexplored. Here we investigate the critical scaling behavior and driven dynamics of the non-Hermitian Aubry-André (AA) model with on-site gain and loss. Through finite-size scaling analyses of the localization length, the inverse participation ratio (IPR), and the energy gap, we extract the critical exponents $ν= 1.00(2)$, $s = 0.7965(2)$, and $z = 1.999(2)$. These exponents are different from those of both the Hermitian AA model and the nonreciprocal hopping AA model, particularly the IPR exponent $s$, demonstrating that the gain-loss mechanism belongs to a distinct universality class. For the driven dynamics, we focus on the case where the system is initially prepared in a gapless extended state and linearly driven across the critical point. We verify that the finite-time scaling (FTS) framework remains applicable provided that the criterion $z' < r$ is satisfied, where $z' = 1.999(2)$ characterizes the gap closure in the extended phase and $r = z + 1/ν\approx 2.999$. The predicted FTS scaling forms for the IPR are numerically validated across a wide range of system sizes and driving rates, demonstrating that the unified scaling description can be successfully generalized to the gain-loss type non-Hermitian AA model. Our work not only establishes the gain-loss AA model as a new universality class of localization transitions but also extends the applicability of the FTS framework to non-Hermitian systems with gapless initial states.

cond-mat.dis-nn↗

arXiv2025

The extended inner shadow of Kerr-Taub-NUT black hole with thin disk flows

In this paper, we apply numerical backward ray-tracing to study the observational appearance of Kerr-Taub-NUT (KTN) black holes illuminated by thin accretion disk flows. We obtained the inner shadow, redshift characteristics, and intensity distribution of thin-disk images of the KTN black hole, as observed by a common observer located at different positions. The results show that increasing the spin parameter progressively deforms the critical curve into a "D" shape while simultaneously shrinking and distorting the inner shadow. More importantly, for n = 0.3 at theta_o = 80 degrees, the inner shadow develops a novel "duck-cap-like" morphology with a sharply protruding lower-right edge beyond the critical curve. We term this feature the "extended inner shadow", a structure distinct from the Kerr case. Unlike the standard inner shadow, it consists partly of photons absorbed by the horizon and partly of photons that avoid both absorption and crossing the disk plane, thus receiving no emission. Such deviations from Kerr predictions could be tested by future high-precision astronomical observations, potentially offering new evidence for the existence of NUT charge (or the gravitomagnetic monopole) in black holes.

gr-qc↗

arXiv2025

NVIDIA Nemotron Nano V2 VL

We introduce Nemotron Nano V2 VL, the latest model of the Nemotron vision-language series designed for strong real-world document understanding, long video comprehension, and reasoning tasks. Nemotron Nano V2 VL delivers significant improvements over our previous model, Llama-3.1-Nemotron-Nano-VL-8B, across all vision and text domains through major enhancements in model architecture, datasets, and training recipes. Nemotron Nano V2 VL builds on Nemotron Nano V2, a hybrid Mamba-Transformer LLM, and innovative token reduction techniques to achieve higher inference throughput in long document and video scenarios. We are releasing model checkpoints in BF16, FP8, and FP4 formats and sharing large parts of our datasets, recipes and training code.

cs.LG↗

arXiv2025

Driven dynamics of localization phase transition in the Aubry-André model with initial gapless extended states

Recently, the driven dynamics of localization phase transitions have garnered growing interest. However, studies so far have mainly considered initial localized states, whose driven dynamics follow the Kibble-Zurek mechanism (KZM). In this study, we investigate the driven dynamics of the localization phase transition in the Aubry-André (AA) model starting from a gapless extended state, which violates the adiabatic-impulse scenario of KZM. By linearly driving the quasiperiodic potential strength across the critical point, we numerically simulate the driven dynamics and analyze the scaling behavior of both the inverse participation ratio ($\mathcal{I}$) and the dynamic deviation from the instantaneous ground state energy $(\mathcal{D})$. We demonstrate that the driven dynamics starting from initially extended states satisfies the criterion for the applicability of KZM and its extension, finite-time scaling (FTS). The scaling functions governing the driven dynamics of both $\mathcal{I}$ and $\mathcal{D}$ have been derived based on FTS and numerically validated. We found that the scaling functions exhibit significant differences at large $R$ and small $R$, and also differ considerably from the scaling functions when the initial state is localized, highlighting the crucial role of initial state behavior. The established scaling laws remain robust across a wide range of system sizes and driving rates, providing testable predictions for experimental realizations.

cond-mat.dis-nn↗

arXiv2025

Non-equilibrium dynamics of localization phase transition in the non-Hermitian Disorder-Aubry-André model

The driven dynamics of localization transitions in a non-Hermitian Disordered Aubry-André (DAA) model are examined under both open boundary conditions (OBC) and periodic boundary conditions (PBC). Through an analysis of the static properties of observables, including the localization length ($ξ$), inverse participation ratio ($\rm IPR$), and energy gap ($ΔE$), we found that the critical exponents examined under PBC are also applicable under OBC. The Kibble-Zurek scaling (KZS) for the driven dynamics in the non-Hermitian DAA systems is formulated and numerically verified for different local-to-local quench directions. The hybrid KZS (HKZS) in the overlapping critical region of non-Hermitian DAA and Anderson localization is proposed and numerically confirmed the validity across a local-to-skin quench direction. This study generalizes the application of the KZS to the dynamical localization transitions within systems featuring dual localization mechanisms.

cond-mat.dis-nn↗

arXiv2025

Hybrid scaling mechanism of critical behavior in the overlapping critical regions of classical and quantum Yang-Lee edge singularities

Recently, the study of scaling behavior in Yang-Lee edge singularities (YLES) has attracted sustained attention. However, the scaling mechanism for the overlapping critical region between classical and quantum YLES remains unclear. In this work, we investigate this question, and a hybrid scaling mechanism is introduced to characterize the scaling behavior in the overlapping regions. The hybrid scaling mechanism asserts that in the overlapping region the scaling behavior can be described by the scaling function for both critical regions simultaneously, and it results in a constraint on the scaling functions. The transverse Ising chain in an imaginary longitudinal field, which exhibits $(0+1)$ dimensional (D) and $(1+1)$ D quantum YLES phase transitions at zero temperature, and $(0+0)$ D and $(1+0)$ D classical YLES phase transitions at finite temperature, is employed as a model to test this hybrid scaling mechanism. The scaling functions in the critical regions of $(0+1)$ D and $(1+1)$ D quantum YLES as well as $(0+0)$ D and $(1+0)$ D classical YLES of such model are systematically investigated. Furthermore, the hybrid scaling mechanisms in overlapping critical regions, particularly between classical and quantum YLES, are thoroughly examined. Through this study, we have established a scaling mechanism capable of describing behaviors in the overlapping critical regions between classical and quantum phase transitions, which also facilitates the extraction of quantum phase transition information from classical phase transition systems.

cond-mat.stat-mech↗

arXiv2025

Infinity Branches and Asymptotic Analysis of Algebraic Space Curves: New Techniques and Applications

Let C represent an irreducible algebraic space curve defined by the real polynomials fi(x1, x2, x3) for i = 1, 2. It is a recognized fact that a birational relationship invariably exists between the points on C and those on an associated irreducible plane curve, denoted as Cp. In this work, we leverage this established relationship to delineate the asymptotic behavior of C by examining the asymptotes of Cp. Building on this foundation, we introduce a novel and practical algorithm designed to efficiently compute the asymptotes of C, given that the asymptotes of Cp have been ascertained.

math.AG↗

arXiv2024

Hybrid scaling properties of localization transition in a non-Hermitian disorder Aubry-André model

In this paper, we study the critical behaviors in the non-Hermitian disorder Aubry-André (DAA) model, and we assume the non-Hermiticity is introduced by nonreciprocal hopping. We employ the localization length $ξ$, the inverse participation ratio ($\rm IPR$), and the energy gap $ΔE$ as the characteristic quantities to describe the critical properties of the localization transition. By performing scaling analysis, the critical exponents of the non-Hermitian Anderson model and the non-Hermitian DAA model are obtained, and these critical exponents are different from their Hermitian counterparts, indicating that the Hermitian and non-Hermitian Anderson and DAA models belong to different universality classes. The critical exponents of the non-Hermitian DAA model are remarkably different from both the pure non-Hermitian AA model and the non-Hermitian Anderson model, showing that disorder is an independent relevant direction at the non-Hermitian AA model critical point. We further propose a hybrid scaling law to describe the critical behavior in the overlapping critical region constituted by the critical regions of the non-Hermitian DAA model and the non-Hermitian Anderson localization.

cond-mat.dis-nn↗

arXiv2023

Robust Trading in a Generalized Lattice Market

This paper introduces a novel robust trading paradigm, called \textit{multi-double linear policies}, situated within a \textit{generalized} lattice market. Distinctively, our framework departs from most existing robust trading strategies, which are predominantly limited to single or paired assets and typically embed asset correlation within the trading strategy itself, rather than as an inherent characteristic of the market. Our generalized lattice market model incorporates both serially correlated returns and asset correlation through a conditional probabilistic model. In the nominal case, where the parameters of the model are known, we demonstrate that the proposed policies ensure survivability and probabilistic positivity. We then derive an analytic expression for the worst-case expected gain-loss and prove sufficient conditions that the proposed policies can maintain a \textit{positive expected profits}, even within a seemingly nonprofitable symmetric lattice market. When the parameters are unknown and require estimation, we show that the parameter space of the lattice model forms a convex polyhedron, and we present an efficient estimation method using a constrained least-squares method. These theoretical findings are strengthened by extensive empirical studies using data from the top 30 companies within the S\&P 500 index, substantiating the efficacy of the generalized model and the robustness of the proposed policies in sustaining the positive expected profit and providing downside risk protection.

q-fin.PM↗

arXiv2023

On Robustness of Double Linear Policy with Time-Varying Weights

In this paper, we extend the existing double linear policy by incorporating time-varying weights instead of constant weights and study a certain robustness property, called robust positive expectation (RPE), in a discrete-time setting. We prove that the RPE property holds by employing a novel elementary symmetric polynomials characterization approach and derive an explicit expression for both the expected cumulative gain-loss function and its variance. To validate our theory, we perform extensive Monte Carlo simulations using various weighting functions. Furthermore, we demonstrate how this policy can be effectively incorporated with standard technical analysis techniques, using the moving average as a trading signal.

math.OC↗

arXiv2022

Limit behavior of a class of Cantor-integers

In this paper, we study a class of Cantor-integers $\{C_n\}_{n\geq 1}$ with the base conversion function $f:\{0,\dots,m\}\to \{0,\dots,p\}$ being strictly increasing and satisfying $f(0)=0$ and $f(m)=p$. Firstly we provide an algorithm to compute the superior and inferior of the sequence $\left\{\frac{C_n}{n^α}\right\}_{n\geq 1}$ where $α=\log_{m+1}^{p+1}$, and obtain the exact values of the superior and inferior when $f$ is a class of quadratic function. Secondly we show that the sequence $\left\{\frac{C_n}{n^α}\right\}_{n\geq 1}$ is dense in the close interval with the endpoints being its inferior and superior respectively. As a consequence, (i) we get the upper and lower pointwise density $1/α$-density of the self-similar measure supported on $\mathfrak{C}$ at $0$, where $\mathfrak{C}$ is the Cantor set induced by Cantor-integers. (ii) the sequence $\{\frac{C_n}{n^α}\}_{n\geq 1}$ does not have cumulative distribution function but have logarithmic distribution functions (given by a specific Lebesgue integral). Lastly we obtain the Mellin-Perron formula for the summation function of Cantor-integers. In addition, we investigate some analytic properties of the limit function induced by Cantor-integers.

math.NT↗