arXiv subjects

Lang Cheng

Publications and source records attributed to Lang Cheng.

7 recordsLinked to original sources

arXiv2026

Early-Time Nonlinear Growth in an Unstable Q-Ball Hairy Black Hole

Early-time evolution away from an unstable equilibrium in a nonlinear system is often expected to be governed by the associated linear instability. Combining full nonlinear evolution with first- and second-order quasinormal mode (QNM) calculations, we show that this expectation can fail during the unstable growth stage of a Q-ball hairy black hole in Einstein-Maxwell theory with a charged self-interacting scalar field. The linear unstable QNM has a much larger amplitude in one component of the scalar field than in the other: the more strongly responding component follows that mode, whereas the early growth of the more weakly responding component is dominated by a second-order QNM sourced by the linear unstable mode. This occurs while the evolution remains perturbative. Our results thus show that the early growth of an individual component need not be governed by its linear response.

gr-qc↗

arXiv2026

PolyReal: A Benchmark for Real-World Polymer Science Workflows

Multimodal Large Language Models (MLLMs) excel in general domains but struggle with complex, real-world science. We posit that polymer science, an interdisciplinary field spanning chemistry, physics, biology, and engineering, is an ideal high-stakes testbed due to its diverse multimodal data. Yet, existing benchmarks related to polymer science largely overlook real-world workflows, limiting their practical utility and failing to systematically evaluate MLLMs across the full, practice-grounded lifecycle of experimentation. We introduce PolyReal, a novel multimodal benchmark grounded in real-world scientific practices to evaluate MLLMs on the full lifecycle of polymer experimentation. It covers five critical capabilities: (1) foundational knowledge application; (2) lab safety analysis; (3) experiment mechanism reasoning; (4) raw data extraction; and (5) performance & application exploration. Our evaluation of leading MLLMs on PolyReal reveals a capability imbalance. While models perform well on knowledge-intensive reasoning (e.g., Experiment Mechanism Reasoning), they drop sharply on practice-based tasks (e.g., Lab Safety Analysis and Raw Data Extraction). This exposes a severe gap between abstract scientific knowledge and its practical, context-dependent application, showing that these real-world tasks remain challenging for MLLMs. Thus, PolyReal helps address this evaluation gap and provides a practical benchmark for assessing AI systems in real-world scientific workflows.

cs.CV↗

arXiv2026

Exceptional Points in Quasinormal Spectra of Hairy Black Holes

Exceptional points (EPs) in quasinormal mode (QNM) spectra are non-Hermitian degeneracies at which both the eigenvalues and eigenfunctions coalesce. In this paper, we identify an EP in the scalar QNM spectrum of hairy black holes in the Einstein-Maxwell-scalar theory by scanning the parameter space. We then investigate its implications for ringdown signals by extracting QNMs from time-domain waveforms. Our results show that an EP ansatz, which includes a resonant contribution containing a term linear in time, provides a more robust description of ringdown at the EP than the standard ansatz based on a superposition of independent damped modes. In particular, it captures the resonant contribution associated with spectral coalescence more naturally, and even when the waveform is fitted with the standard ansatz, the resulting fit may still exhibit characteristic features of the EP ansatz.

gr-qc↗

arXiv2025

Rotating Black Holes in Einstein-Born-Infeld Theory

We numerically construct a family of stationary, axisymmetric black hole solutions in Einstein-Born-Infeld theory, incorporating both electric charge and rotation. Our results indicate that when nonlinear electromagnetic effects are weak, rotating BI black holes with fixed spin approach the extremal limit as the electric charge increases. In contrast, strong nonlinear effects lead to the termination of solutions at configurations corresponding to naked singularities. We demonstrate that nonlinear electrodynamics enhances the gyromagnetic ratio relative to that of Kerr-Newman (KN) black holes. Additionally, we analyze the Innermost Stable Circular Orbits (ISCOs) and find that both prograde and retrograde ISCO radii are consistently smaller than those found in KN black holes.

gr-qc↗

arXiv2025

Spin-induced Scalarized Black Holes in Einstein-Maxwell-scalar Models

We construct spin-induced scalarized black hole solutions in a class of Einstein-Maxwell-scalar models, where a scalar field is non-minimally coupled to the electromagnetic field. Our results show that scalar hair develops only for rapidly rotating black holes, while slowly spinning ones remain well described by the Kerr-Newman (KN) metric. The scalar field contributes only a small fraction of the total mass, indicating suppressed nonlinear effects. This suppression may account for the narrow existence domains of scalarized black holes and the similarities observed in their existence domains across different coupling functions. Moreover, scalarized black holes are found to coexist with linearly stable, entropically favored KN black holes. These results motivate further investigations into the nonlinear dynamics and stability of scalarized black holes in these models.

gr-qc↗

arXiv2024

Polarized Image of a Synchrotron-emitting Ring in Einstein-Maxwell-scalar Theory

This study investigates polarized images of an equatorial synchrotron-emitting ring surrounding hairy black holes within the Einstein-Maxwell-scalar theory. Our analysis demonstrates qualitative similarities between the polarization patterns of hairy black holes and Schwarzschild black holes. However, due to the non-minimal coupling between the scalar and electromagnetic fields, an increase in black hole charge and coupling constant can substantially amplify polarization intensity and induce deviations in the electric vector position angle. These effects may offer observational signatures to distinguish hairy black holes from Schwarzschild black holes.

gr-qc↗

arXiv2024

Observational Signatures of Traversable Wormholes

In this paper, we study the observational signatures of traversable Simpson-Visser wormholes illuminated by luminous celestial spheres and orbiting hot spots. We demonstrate that when light sources and observers are on the same side of the wormholes, the images of the wormholes mimic those of black holes. However, when the light sources are positioned on the opposite side from observers, photons traversing the wormhole throat generate distinct observational signatures. Specifically, unlike black hole images, the wormhole images are confined within the critical curve, resulting in smaller centroid variations. Furthermore, the light curve of hot spots can exhibit additional peaks.

gr-qc↗