arXiv subjects

Ling Sun

Publications and source records attributed to Ling Sun.

At least 19 recordsLinked to original sources

arXiv2026

Tracing source imprints on the gravitational direct wave

The direct wave component of black hole (BH) ringdown, revealed through quasinormal-mode filters, carries a non-quasinormal-mode imprint of the plunging perturber's dynamics. However, the connection between the source trajectory and the observed direct wave remains incompletely understood. We first show that the full waveform filtered by the frequency-dependent black hole response gives a substantially more localized kernel than the standard rational filter approach. We then show that analytically continuing the Teukolsky source variables to complex coordinates allows for a semianalytic direct wave which closely reproduces numerical integration throughout the entire plunge. Our generalized steepest-descent method clarifies how coherent emission shapes the imprint of source dynamics on the observed direct wave beyond the light-cone picture.

gr-qc↗

arXiv2026

Accounting for detector calibration uncertainty in black-hole ringdown analysis

Detector calibration systematics can bias measurements of a remnant black hole's mass and spin, producing spurious evidence against general relativity if unaccounted for. The ringdown phase in the gravitational-wave signal produced by a binary black-hole merger encodes the remnant properties: at sufficiently late times, the signal is well described by a superposition of quasinormal modes, each with a frequency and damping time set only by the remnant mass and spin. Here we present two complementary approaches for analyzing the ringdown portion of the data to estimate the remnant mass and spin in the presence of a nonnegligible detector calibration error, using the quasinormal-mode rational filter (QNMRF). With a well-measured error, we apply the best-estimated calibration correction to the strain before conducting the standard analysis; with an unknown error, we instead jointly sample the remnant mass, spin and the frequency-dependent calibration error, marginalizing over an uncertainty prior. By injecting the numerical-relativity waveform SXS:BBH:0305 into colored detector noise, at a full-signal matched-filter signal-to-noise ratio of $\sim60$ and with simulated calibration errors of $\pm25\%$ in magnitude and $\pm25^\circ$ in phase, marginalizing over the calibration uncertainty recovers the true mass and spin within the 90\% credible interval, whereas the estimated values are biased if the calibration errors are ignored. We apply the method to GW250207, an event recorded while the Hanford detector response was not well characterized, and recover a remnant consistent with the inspiral-merger-ringdown prediction using the ringdown portion alone, both by correcting for a best-estimated calibration error and by marginalizing over a broad uncertainty prior.

gr-qc↗

arXiv2026

Systematic Uncertainties in Ultralight Boson Constraints from Superradiance

Ultralight bosons are well-motivated candidates for physics beyond the Standard Model and may constitute part or all of the dark matter. Black-hole superradiance provides a powerful means of probing these particles through their gravitational interaction with rotating black holes. This mechanism has motivated a growing body of constraints from electromagnetic measurements of black-hole spins and, more recently, gravitational-wave observations. Gravitational-wave probes draw on several distinct signatures: the spins of merging binary black holes, gravitational radiation emitted by boson clouds, and potential imprints of cloud-induced changes to binary dynamics. The interpretation of these probes depends on method-specific astrophysical and theoretical assumptions, including black hole formation, natal spin, age, accretion history, population priors, and boson self-interactions. In this paper, we review the principal electromagnetic and gravitational-wave constraints derived from black-hole superradiance, with particular emphasis on their underlying assumptions and systematic uncertainties. The distinct observational signatures and systematic uncertainties of these approaches offer complementary perspectives on the viability of ultralight-boson models. In particular, their overlapping coverage around boson masses of $10^{-13}$-$10^{-12}$ eV makes this region particularly informative for comparing constraints, with attention to the assumptions underlying each result.

hep-ph↗

arXiv2026

Complex frequency evolution of direct waves from binary black hole mergers

While no signal originating at a black hole's event horizon can reach future null infinity, information about the horizon and its immediate vicinity can be encoded in asymptotic properties of waves emitted by matter or field perturbations falling toward a growing/forming horizon. Within a response-filtered framework, "direct wave" denotes source-sensitive plunge and remnant-formation information revealed by filtering the black-hole response. Unlike a stationary damped sinusoid with a fixed complex frequency, the direct wave follows the evolving source and has an evolving instantaneous complex frequency tied at late times to the remnant horizon angular velocity $Ω_H$ and surface gravity $κ_H$. Using rational filters, we remove quasinormal modes from numerical-relativity waveforms to study this evolution. Before numerical contamination, trajectories depend on remnant spin: the real frequency evolves toward $2Ω_H$ from above for lower spins ($χ_f\lesssim0.7$) and from below for higher spins ($χ_f\gtrsim0.7$), while the instantaneous decay rate increases, with best-resolved cases approaching the expected value of $3κ_H$. As in particle-plunge results, the horizon-controlled value is approached only at late times, as frame dragging controls near-horizon motion. For $χ_f\sim0.7$ remnants of non-precessing, comparable-mass binaries, the early-time real frequency is close to $2Ω_H$ because the binary orbital frequency transitions smoothly to the remnant horizon frequency. Finite-time deviations therefore carry information about merger/collapse dynamics rather than undermining the horizon connection. Full direct-wave evolution requires numerical-relativity calibration. We further show that approximate pole-zero pairing in the Kerr response motivates a minimal filter set that suppresses quasinormal-mode features while revealing source-trajectory information.

gr-qc↗

arXiv2026

A semicoherent resampling method for long-transient gravitational wave searches with applications to subsolar-mass primordial black-hole binaries

Resampling removes the modeled phase evolution of a frequency-evolving signal, transforming it into a monochromatic one. We introduce a novel implementation for long-transient gravitational-wave searches that evaluates the Fourier spectrum of the resampled data using a type-I non-uniform fast Fourier transform (NUFFT). This implementation can be up to two orders of magnitude faster than some previous implementations, depending on coherent length, sampling rate, and desired accuracy. To demonstrate its application, we benchmark the method with a semicoherent search for long-duration inspiral signals from subsolar-mass primordial black hole binaries. For a search over $40$--$60\,\mathrm{Hz}$ and chirp masses of $5\times10^{-4}$--$10^{-1}\,M_\odot$, with a coherent duration of $30\,\mathrm{s}$ and a realistic computing cost, the estimated horizon distance exceeds the Galactic Center for all of the parameter space considered and exceeds Andromeda for chirp masses above approximately $2\times10^{-2}M_\odot$. These results establish NUFFT-based resampling as a computationally efficient and broadly applicable approach for searches for modeled, frequency-evolving gravitational-wave signals.

gr-qc↗

arXiv2026

From driven oscillations to free ringdown: a particle plunging into Kerr

We show that a ringdown waveform can admit a constant-coefficient quasinormal-mode (QNM) representation while its individual QNM-pole contributions remain driven. To establish this result, we construct a first-principles rational approximation to the Kerr Green's function from its QNM poles, physical residues, and horizon-frequency zeros. For particles plunging from the innermost stable circular orbit into Kerr black holes with spins 0.5-0.9, each QNM-pole contribution initially follows the source's instantaneous complex frequency and decouples only after the source decays faster than the corresponding mode. At late times, the source approaches a sum of damped oscillations at the third and higher horizon frequencies. The corresponding zeros in the Green's function cancel these source-frequency components in the coherent waveform, while the continuing drive generates oscillations at QNM frequencies. Thus, an apparently free QNM superposition can emerge before its individual contributions dynamically decouple from the source.

gr-qc↗

arXiv2026

A Tale of Two Calibrators: Comparing Newtonian and Photon Calibration in Advanced LIGO after the Third Observing Run

Precise calibration of LIGO's strain readout plays a vital role in our ability to extract information from gravitational-wave detections. We present a comparative analysis of two independent direct-force calibration methods: the Newtonian Calibrator (NCal) and Photon Calibrator (PCal) systems. Currently, LIGO relies solely on the PCal system as its absolute calibration reference. To facilitate comparison, a series of direct-force injections were performed using the NCal and PCal systems at the LIGO Hanford observatory just after the completion of the third observing run. We compute the ratio of the measured to expected strain amplitudes for every injection. For each injection frequency across a 30 Hz band, the ratios of NCal and PCal differ by $\sim$0.5-1%, demonstrating a small systematic difference between the two systems. This offset highlights the importance of maintaining multiple independent calibration references to validate LIGO's calibration.

gr-qc↗

arXiv2026

Spotlight searches for continuous gravitational waves triggered on radiometer candidates in LIGO O4a data

We report on a follow-up search for continuous gravitational waves (CWs) targeting sub-threshold candidates from the O4a LIGO-Virgo-KAGRA (LVK) all-sky all-frequency (ASAF) directed radiometer analysis. We analyze a total of $562$ ASAF candidates using Advanced LIGO data from the first part of the fourth LVK observing run. Each candidate comprises a narrow $1/32$ Hz frequency band paired with a ${\sim}13$ deg$^2$ sky pixel, defining the search parameter space for our analysis. Our search pipeline leverages the $F$-statistic matched filter equipped with a hidden Markov model to enable tracking of a potentially frequency-wandering CW signal. Of the 562 initial candidates, we obtain $21$ outliers with false alarm probability less than $5\%$ that survive all instrumental vetoes. None of the outliers are recovered at comparable statistical significance in the second part of the fourth observing run, from which we conclude that no convincing CW signals are detected. We estimate the sensitivity of our analysis by recovering simulated signals added to real detector data. Across the $20\text{--}1726$ Hz frequency band, our search achieves $95\%$ detection efficiency for strain amplitudes in the range of $h_0\sim (0.63\text{--}6.3)\times10^{-25}$ with respect to isolated neutron stars (NSs), and $h_0\sim (0.82\text{--}7.1)\times10^{-25}$ with respect to NSs in long-period ($>1$ yr) binary systems. The large range in sensitivity is due to the strong frequency dependence of detector noise, particularly at low frequencies.

gr-qc↗

arXiv2026

GW250114 reveals black hole horizon signatures

The horizon of a black hole, the "surface of no return", is characterized by its rotation frequency $Ω_H$ and surface gravity $κ$. A striking signature is that any infalling object appears to orbit at $Ω_H$ due to frame dragging, while its emitted signals decay exponentially at a rate set by $κ$ as a consequence of gravitational redshift. Recent theoretical work predicts that the merger phase of gravitational waves from binary black hole coalescences carries direct imprints of the remnant horizon's properties, via a "direct wave" component that (i) oscillates near $2Ω_H$, reflecting the horizon's frame dragging and the dominant quadrupole nature of the gravitational radiation, and (ii) decays at an increasing rate characterized by $κ$, with additional screening from the black hole's potential barrier. In this paper, we report observational evidence for the direct wave in GW250114, with a 90\% credible matched-filter signal-to-noise ratio of $15.8^{+0.1}_{-0.5}$ ($17.1^{+0.1}_{-0.4}$) in the LIGO Hanford (Livingston) detector. The measured properties are in full agreement with theoretical predictions. These findings establish a new observational channel to directly measure frame-dragging effects in black hole ergospheres and explore (near-)horizon physics in dynamical, strong-gravity regimes.

gr-qc↗

arXiv2026

Ultralight boson constraints from gravitational wave observations of spinning binary black holes

In the presence of an ultralight scalar or vector boson, a spinning black hole will be spun down through the superradiant instability. We use spin measurements from gravitational wave observations of binary black holes, in particular the heavy binary black hole merger event GW231123, along with the lower-mass GW190517 event, to constrain the existence of ultralight bosons. We disfavor scalars with masses in the range of $[0.55, 11]\times 10^{-13}$ eV and vectors in the range of $[0.11, 18]\times 10^{-13}$ eV, making only a conservative assumption that the black hole lifetimes are greater than $10^5$ years. The lower ends of these ranges, where the exclusion confidence is the highest, were not previously excluded by spin measurements from electromagnetic or gravitational wave observations. We map these constraints to axion and dark photon models with interactions.

gr-qc↗

arXiv2025

Proficiency-Aware Adaptation and Data Augmentation for Robust L2 ASR

General-purpose ASR underperforms for atypical speakers, such as L2 learners, reinforcing bias and limiting use in education and accessibility. Using the CEFR-graded Speak and Improve corpus, we show that naive fine-tuning of Whisper reduces average WER but simultaneously widens disparities and disproportionately harms lower-level learners. To address this, we propose two strategies: (i) proficiency-aware multitask learning, jointly optimizing ASR with proficiency classification, and (ii) targeted augmentation, applying spectrogram masking to low-proficiency speech to counter imbalance. These approaches reduce WER by up to 29.4 percent (relative) and insertion/deletion errors by as much as 58.6 percent (relative). Crucially, despite the severe imbalance of the dataset reflecting real-world distributions, both strategies consistently narrow proficiency gaps, advancing equitable ASR for L2 learners.

cs.SD↗

arXiv2025

Quantum NLP models on Natural Language Inference

Quantum natural language processing (QNLP) offers a novel approach to semantic modeling by embedding compositional structure directly into quantum circuits. This paper investigates the application of QNLP models to the task of Natural Language Inference (NLI), comparing quantum, hybrid, and classical transformer-based models under a constrained few-shot setting. Using the lambeq library and the DisCoCat framework, we construct parameterized quantum circuits for sentence pairs and train them for both semantic relatedness and inference classification. To assess efficiency, we introduce a novel information-theoretic metric, Information Gain per Parameter (IGPP), which quantifies learning dynamics independent of model size. Our results demonstrate that quantum models achieve performance comparable to classical baselines while operating with dramatically fewer parameters. The Quantum-based models outperform randomly initialized transformers in inference and achieve lower test error on relatedness tasks. Moreover, quantum models exhibit significantly higher per-parameter learning efficiency (up to five orders of magnitude more than classical counterparts), highlighting the promise of QNLP in low-resource, structure-sensitive settings. To address circuit-level isolation and promote parameter sharing, we also propose a novel cluster-based architecture that improves generalization by tying gate parameters to learned word clusters rather than individual tokens.

cs.CL↗

arXiv2025

Impact of Detector Calibration Accuracy on Black Hole Spectroscopy

Systematic errors in detector calibration can bias signal analyses and potentially lead to incorrect interpretations suggesting violations of general relativity. In this study, we investigate how calibration systematics affect black hole (BH) spectroscopy, a technique that uses the quasinormal modes (QNMs) emitted during the ringdown phase of gravitational waves (GWs) to study remnant BHs formed in compact binary coalescences. We simulate a series of physically motivated, tunable calibration errors and use them to intentionally miscalibrate numerical relativity waveforms. We then apply a QNM extraction method -- the rational QNM filter -- to quantify the impact of these calibration errors. We find that current calibration standards (errors within $10\%$ in magnitude and $10^\circ$ in phase across the most sensitive frequency range of 20--2000 Hz) are adequate for BH ringdown analyses with existing observations, but insufficient for the accuracy goals of future upgraded and next-generation observatories. Specifically, we show that for events with a high ringdown signal-to-noise ratio of $\sim 120$, calibration errors must remain $\lesssim 4\%$ in magnitude and $\lesssim 4^\circ$ in phase to avoid introducing biases. While this analysis focuses on a particular aspect of BH spectroscopy, the results offer quantitative benchmarks for calibration standards crucial to fully realize the potential of precision tests of general relativity in the next-generation detector era.

gr-qc↗

arXiv2025

Statistical identification of ringdown modes with rational filters

Measuring quasinormal modes (QNMs) during the ringdown phase of binary black hole coalescences provides key insights into merger dynamics and enables tests of the no-hair theorem. The QNM rational filter has recently been introduced as a technique to identify specific QNMs in ringdown signals without sampling over mode amplitudes and phases. In this work, we extend the QNM rational filter framework to quantify the statistical confidence of subdominant mode detections in real gravitational wave (GW) observations. We employ a frequentist approach to estimate false-alarm probabilities and propose a workflow for robust identification of specific QNMs. We first validate our methodology using synthetic signals generated from numerical relativity waveforms. We then reanalyze the first GW event, GW150914, finding a marginal detection of an overtone, but at time when the applicability of constant amplitude QNM fits is not fully understood. This extended methodology provides a systematic approach to improving the reliability of QNM detections, paving the way for more precise tests of strong-field gravity with current and future GW observations.

gr-qc↗

arXiv2025

A Unified Framework for Interactive Visual Graph Matching via Attribute-Structure Synchronization

In traditional graph retrieval tools, graph matching is commonly used to retrieve desired graphs from extensive graph datasets according to their structural similarities. However, in real applications, graph nodes have numerous attributes which also contain valuable information for evaluating similarities between graphs. Thus, to achieve superior graph matching results, it is crucial for graph retrieval tools to make full use of the attribute information in addition to structural information. We propose a novel framework for interactive visual graph matching. In the proposed framework, an attribute-structure synchronization method is developed for representing structural and attribute features in a unified embedding space based on Canonical Correlation Analysis (CCA). To support fast and interactive matching, \revise{our method} provides users with intuitive visual query interfaces for traversing, filtering and searching for the target graph in the embedding space conveniently. With the designed interfaces, the users can also specify a new target graph with desired structural and semantic features. Besides, evaluation views are designed for easy validation and interpretation of the matching results. Case studies and quantitative comparisons on real-world datasets have demonstrated the superiorities of our proposed framework in graph matching and large graph exploration.

cs.IR↗

arXiv2025

Methodology for constraining ultralight vector bosons with gravitational wave searches targeting merger remnant black holes

Ultralight bosons are a hypothetical class of particles predicted under various extensions of Standard Model physics. As a result of the superradiance mechanism, we expect ultralight bosons, should they exist in certain mass ranges, to form macroscopic clouds around rotating black holes, so that we can probe their existence by looking for the long-transient gravitational wave emission produced by such clouds. In this paper, we propose a statistically robust framework for constraining the existence of ultralight vector bosons in the absence of detecting such a signal from searches targeting merger remnant black holes, effectively marginalizing over the uncertainties present in the properties of the target black holes. We also determine the impact of weak kinetic mixing with the ordinary photon and vector mass generation through a hidden Higgs mechanism on the constraining power of these searches. We find that individual follow-up searches, particularly with the next-generation gravitational wave detectors, can probe regions of parameter space for such models where robust constraints are still lacking.

gr-qc↗

arXiv2025

Differential torsion sensor for direct detection of ultralight vector dark matter

Ultralight bosons with masses in the range from $\sim 10^{-22}$ eV/$c^2$ to $\sim 1$ eV/$c^2$, are well-motivated, wave-like dark matter candidates. Particles on the lower-mass end are less explored in experiments due to their vanishingly small mass and weak coupling to the Standard Model. We propose a sensor with dual torsion pendulums for the direct detection of U(1)$_{B\!-\!L}$ gauge boson dark matter, which can achieve an enhanced differential torque sensitivity in a frequency band of $\sim 10^{-2}$-$10$ Hz due to its advantages in common-mode rejection and differential angular sensitivity. We describe the design of the differential torsion sensor and present the estimated sensitivity to an ultralight dark matter field coupled to baryon minus lepton ($B\!-\!L$) number, in a mass range of $\sim 10^{-17}$-$10^{-13}$ eV/$c^2$. Given a setup with meter-scale torsion pendulum beams and kg-scale test masses, the projected constraints on the coupling constant $g_{B\!-\!L}$ can reach $\sim 10^{-27}$ for a boson mass of $\sim 10^{-15}$ eV/$c^2$.

hep-ph↗

arXiv2025

Mapping inspiral-merger-ringdown waveforms of binary black holes from black hole perturbation waveforms by machine learning

Identifying weak gravitational wave signals in noise and estimating the source properties require high-precision waveform templates. Numerical relativity (NR) simulations can provide the most accurate waveforms. However, it is challenging to compute waveform templates in high-dimensional parameter space using NR simulations due to high computational costs. In this work, we implement a novel waveform mapping method, which is an alternative approach to the existing analytical approximations, based on closed-form continuous-time neural networks. This machine-learning-based method greatly improves the efficiency of calculating waveform templates for arbitrary source parameters, such as the binary mass ratio and the spins of component black holes. Based on this method, we present \textit{BHP2NRMLSur}, a class of models (including nonspinning and spin-aligned ones) that maps point-particle black hole perturbation theory waveforms into NR and surrogate waveforms. The nonspinning model provides highly accurate waveforms that match the NR waveforms to the level of $\gtrsim 0.995$. The spin-aligned model reduces the required input parameters and hence improves the efficiency of the waveform generation -- it takes a factor of $\sim 50$ less time than existing NR surrogate models to generate $100,000$ waveforms, with a mismatch of $<0.01$ compared to the NR waveforms from the Simulating eXtreme Spacetimes collaboration.

gr-qc↗