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Kun Cheng

Publications and source records attributed to Kun Cheng.

At least 37 records · Page 2Linked to original sources
arXiv2025

Quantum Information meets High-Energy Physics: Input to the update of the European Strategy for Particle Physics

Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown and has gathered the attention of the scientific community. For the range of particles and fundamental interactions involved, particle colliders provide a novel environment where quantum information theory can be probed, with energies exceeding by about 12 orders of magnitude those employed in dedicated laboratory setups. Furthermore, collider detectors have inherent advantages in performing certain quantum information measurements, and allow for the reconstruction of the state of the system under consideration via quantum state tomography. Here, we elaborate on the potential, challenges, and goals of this innovative and rapidly evolving line of research and discuss its expected impact on both quantum information theory and high-energy physics.

hep-ph↗
arXiv2025

Coupled Modeling of External Pressure and Capillary Blood Flow: Nonlinear Dynamics of Vascular Elasticity and Collapse Effects

External pressure significantly influences microcirculatory capillary blood flow, yet current studies lack quantitative modeling. This work proposes a nonlinear segmented coupling model between external pressure and capillary flow, incorporating vascular elasticity and collapse effects. The pressure-flow response is divided into three phases: elastic compression under low pressure (less than 30 mmHg), elliptical collapse in the transition zone (30 to 40 mmHg), and closure-induced attenuation under high pressure (above 40 mmHg), with explicit expressions derived for each. Parameter sensitivity analysis and comparison with literature demonstrate the model's capability in capturing key determinants. The proposed framework supports dose-response assessment and individualized parameter tuning in pressure-based therapies such as tourniquets and compression garments.

physics.bio-ph↗
arXiv2025

Quantum Tomography in Neutral Meson and Antimeson Systems

The flavor space of particles produced in collider environments contains informative quantum correlations. We present a systematic approach for constructing the complete flavor density matrix for a meson and antimeson system ($M \bar M$) in the Bloch vector space at a given time $t$, which can be at or after production. We point out that the $B_s^0$ and $K^0$ systems are superior to the $B^0_d$ and $D^0$ systems for quantum tomography because of their flavor oscillation and decay properties. Performing quantum tomography for the $M \bar M$ system can facilitate the study of production mechanisms, decoherence phenomena, quantum information variables, and potential new sources of CP violation.

hep-ph↗
arXiv2025

Bell Inequality Violation of Light Quarks in Back-to-Back Dihadron Pair Production at Lepton Colliders

Spin correlations between particles produced at colliders provide valuable insights for quantum information studies. While traditional studies of quantum information at colliders are typically limited to massive particles with perturbative decay, we propose an innovative method to explore the Bell inequality in massless quark pair systems by analyzing the azimuthal correlations in back-to-back $π^+π^-$ dihadron pair production at lepton colliders. Revisiting the Belle data, we have shown the potential to detect Bell inequality violation of light quarks by introducing an additional angular cut, achieving a significance of 2.5 $σ$ even in the worst-case scenario of 100% correlated systematic uncertainties in each bins. The significance substantially exceeds $5σ$ when considering uncorrelated systematic uncertainties. Our approach opens avenues for exploring spin quantum information in the non-perturbative aspect and leverages existing data for quantum information research.

hep-ph↗
arXiv2025

Maximizing the Azimuthal-Angle Correlation in the Decay of Vector Boson Pairs

Spin correlation observables of particles produced at colliders generally depend on the coordinate basis. While spin correlations and their associated basis dependence have been studied in top-quark pair production, the basis dependence of spin correlations of a $W^\pm$ pair has not been studied. In this work, we focus on the azimuthal-angle correlation in the decay of a $W^\pm$ pair, which encodes spin information in the direction transverse to the rotational axis. We quantitatively describe the basis dependence of the relative azimuthal angle. We further present the optimal coordinate direction to define the azimuthal angle between the decay products of $W^\pm$ bosons to achieve the maximal spin correlation based on symmetry considerations. The results can be used to optimize the measurement of the CP-even and CP-odd interactions, and have applications to quantum information observables in the vector boson pair system.

hep-ph↗
arXiv2025

Quantum Tomography at Colliders: With or Without Decays

The interpretation of groups of particle spins at colliders as quantum states has opened up the possibility of using colliders for quantum information. While most efforts have focused on utilizing the decays of the particles to infer their spins to reconstruct the quantum density matrix, we show that the production kinematics of the particles provides sufficient information about the spins to establish quantum tomography without using the decays. We perform a comparative study, highlighting the advantages and disadvantages of using this "kinematic approach" relative to the usual "decay approach." Since the kinematic approach leverages the simplicity of scattering kinematics, this approach promises to achieve the optimal statistical results for quantum tomography at colliders.

hep-ph↗
arXiv2025

Round Attention: A Novel Round-Level Attention Mechanism to Accelerate LLM Inference

The increasing context window size in large language models (LLMs) has improved their ability to handle complex, long-text tasks. However, as the conversation rounds continue, it is required to store a large amount of KV cache in GPU memory, which significantly affects the efficiency and even availability of the model serving systems. This paper analyzes dialogue data from real users on the granularity of round and discovers that the LLM inference manifests a watershed layer, after which the distribution of round-level attention shows notable similarity. Based on this, we propose Round Attention - a novel round-level attention mechanism that selectively processes the KV cache of top-k relevant rounds, where k is dynamically determined through the attention matrix in the watershed layer. Theoretical analysis demonstrates that our method reduces memory usage by 54\% to 82\%, while experimental results confirm that loading sparse critical-round KV cache maintains answer accuracy without performance degradation.

cs.CL↗
arXiv2025

A generalization of the Chvátal-Erdős theorem

A well-known result of Chvátal and Erdős from 1972 states that a graph with connectivity not less than its independence number plus one is hamiltonian-connected. A graph $G$ is called an $[s,t]$-graph if any induced subgraph of $G$ of order $s$ has size at least $t.$ We prove that every $k$-connected $[k+1,2]$-graph is hamiltonian-connected except $kK_1\vee G_{k},$ where $k\ge 2$ and $G_{k}$ is an arbitrary graph of order $k.$ This generalizes the Chvátal-Erdős theorem.

math.CO↗
arXiv2025

Sub-MHz Radio Background from Ultralight Dark Photon Dark Matter

Dark photons are a well-motivated candidate for dark matter, but their detection becomes challenging for ultralight masses with both experimental and astrophysical probes. In this work, we propose a new approach to explore this regime through the dark inverse Compton scattering of ultralight dark photons with cosmic ray electrons and positrons. We show this process generates a potentially observable background radiation that is most prominent at frequencies below MHz. We compute this effect using the latest cosmic ray models and radio absorption maps. Comparing it to observations of the Milky Way's radio spectrum from Explorer 43, Radio Astronomy Explorer 2, and the Parker Solar Probe, we place leading constraints on the kinetic mixing of dark photon dark matter for masses $\lesssim 2 \times 10^{-17} \ \rm eV$.

hep-ph↗
arXiv2024

Connected triangle-free planar graphs whose second largest eigenvalue is at most 1

Let $λ_2$ be the second largest eigenvalue of the adjacency matrix of a connected graph. In 2023, Li and Sun \cite{LiSun1} determined all the connected $\{K_{2,3}, K_4\}$-minor free graphs whose second largest eigenvalue $λ_2\le 1$. As a continuance of it, in this paper we completely identify all the connected $\{K_5,K_{3,3}\}$-minor free graphs without $C_3$ whose second largest eigenvalue does not exceed 1. This partially solves an open problem posed by Li and Sun \cite{LiSun1}: Characterize all connected planar graphs whose second largest eigenvalue is at most $1.$ Our main tools include the spectral theory and the local structure characterization of the planar graph with respect to its girth.

math.CO↗
arXiv2024

Constructions of minimally $t$-tough regular graphs

A non-complete graph $G$ is said to be $t$-tough if for every vertex cut $S$ of $G$, the ratio of $|S|$ to the number of components of $G-S$ is at least $t$. The toughness $τ(G)$ of the graph $G$ is the maximum value of $t$ such that $G$ is $t$-tough. A graph $G$ is said to be minimally $t$-tough if $τ(G)=t$ and $τ(G-e)<t$ for every $e\in E(G)$. In 2003, Kriesell conjectured that every minimally $1$-tough graph contains a vertex of degree $2$. In 2018, Katona and Varga generalized this conjecture, asserting that every minimally $t$-tough graph contains a vertex of degree $\lceil 2t \rceil$. Recently, Zheng and Sun disproved the generalized Kriesell conjecture by constructing a family of $4$-regular graphs of even order. They also raised the question of whether there exist other minimally $t$-tough regular graphs that do not satisfy the generalized Kriesell conjecture. In this paper, we provide an affirmative answer by constructing a family of $4$-regular graphs of odd order, as well as a family of 6-regular graphs of order $3k+1~(k\geq 5)$.

math.CO↗
arXiv2024

Sparse graphs with an independent or foresty minimum vertex cut

A connected graph is called fragile if it contains an independent vertex cut. In 2002 Chen and Yu proved that every connected graph of order $n$ and size at most $2n-4$ is fragile, and in 2013 Le and Pfender characterized the non-fragile graphs of order $n$ and size $2n-3.$ It is natural to consider minimum vertex cuts. We prove two results. (1) Every connected graph of order $n$ with $n\ge 7$ and size at most $\lfloor 3n/2\rfloor$ has an independent minimum vertex cut; (2) every connected graph of order $n$ with $n\ge 7$ and size at most $2n$ has a foresty minimum vertex cut. Both results are best possible.

math.CO↗
arXiv2024

Effective Diffusion Transformer Architecture for Image Super-Resolution

Recent advances indicate that diffusion models hold great promise in image super-resolution. While the latest methods are primarily based on latent diffusion models with convolutional neural networks, there are few attempts to explore transformers, which have demonstrated remarkable performance in image generation. In this work, we design an effective diffusion transformer for image super-resolution (DiT-SR) that achieves the visual quality of prior-based methods, but through a training-from-scratch manner. In practice, DiT-SR leverages an overall U-shaped architecture, and adopts a uniform isotropic design for all the transformer blocks across different stages. The former facilitates multi-scale hierarchical feature extraction, while the latter reallocates the computational resources to critical layers to further enhance performance. Moreover, we thoroughly analyze the limitation of the widely used AdaLN, and present a frequency-adaptive time-step conditioning module, enhancing the model's capacity to process distinct frequency information at different time steps. Extensive experiments demonstrate that DiT-SR outperforms the existing training-from-scratch diffusion-based SR methods significantly, and even beats some of the prior-based methods on pretrained Stable Diffusion, proving the superiority of diffusion transformer in image super-resolution.

cs.CV↗
arXiv2024

One Step Diffusion-based Super-Resolution with Time-Aware Distillation

Diffusion-based image super-resolution (SR) methods have shown promise in reconstructing high-resolution images with fine details from low-resolution counterparts. However, these approaches typically require tens or even hundreds of iterative samplings, resulting in significant latency. Recently, techniques have been devised to enhance the sampling efficiency of diffusion-based SR models via knowledge distillation. Nonetheless, when aligning the knowledge of student and teacher models, these solutions either solely rely on pixel-level loss constraints or neglect the fact that diffusion models prioritize varying levels of information at different time steps. To accomplish effective and efficient image super-resolution, we propose a time-aware diffusion distillation method, named TAD-SR. Specifically, we introduce a novel score distillation strategy to align the data distribution between the outputs of the student and teacher models after minor noise perturbation. This distillation strategy enables the student network to concentrate more on the high-frequency details. Furthermore, to mitigate performance limitations stemming from distillation, we integrate a latent adversarial loss and devise a time-aware discriminator that leverages diffusion priors to effectively distinguish between real images and generated images. Extensive experiments conducted on synthetic and real-world datasets demonstrate that the proposed method achieves comparable or even superior performance compared to both previous state-of-the-art (SOTA) methods and the teacher model in just one sampling step. Codes are available at https://github.com/LearningHx/TAD-SR.

cs.CV↗
arXiv2024

Optimizing Fictitious States for Bell Inequality Violation in Bipartite Qubit Systems

There is a significant interest in testing quantum entanglement and Bell inequality violation in high-energy experiments. Since the analyses in high-energy experiments are performed with events statistically averaged over phase space, the states used to determine observables depend on the choice of coordinates through an event-dependent basis and are thus not genuine quantum states, but rather "fictitious states." We prove that if Bell inequality violation is observed with a fictitious state, then it implies the same for a quantum sub-state. We further show analytically that the basis which diagonalizes the spin-spin correlations is optimal for constructing fictitious states, and for maximizing the violation of Bell's inequality.

hep-ph↗
arXiv2024

Hadronic Mono-$W'$ Probes of Dark Matter at Colliders

Particle collisions at the energy frontier can probe the nature of invisible dark matter via production in association with recoiling visible objects. We propose a new potential production mode, in which dark matter is produced by the decay of a heavy dark Higgs boson radiated from a heavy $W'$ boson. In such a model, motivated by left-right symmetric theories, dark matter would not be pair produced in association with other recoiling objects due to its lack of direct coupling to quarks or gluons. We study the hadronic decay mode via $W'\rightarrow tb$ and estimate the LHC exclusion sensitivity at 95\% confidence level to be $10^2-10^5$ fb for $W'$ boson masses between 250 and 1750 GeV.

hep-ph↗
arXiv2024

Global Symmetries and Effective Potential of 2HDM in Orbit Space

We extend the framework of analyzing the 2HDM in its orbit space to study the one-loop effective potential before and after electroweak symmetry breaking. In this framework, we present a comprehensive analysis of global symmetries of the one-loop thermal effective potential in the 2HDM, demonstrating when the global symmetries of the tree-level 2HDM potential are broken by loop contributions. By introducing light-cone coordinates and generalizing the bilinear notation around the vacuum, we present a geometric view of the scalar mass matrix and on-shell renormalization conditions.

hep-ph↗