arXiv subjects

Xuan Luo

Publications and source records attributed to Xuan Luo.

At least 73 records · Page 4Linked to original sources

arXiv2024

The Theoretical Study of $Σ^{+} p \toΛa_0^{+} p$ Reaction

We conducted a theoretical study on the process $Σ^{+} p \toΛa_0^{+} p$ based on an effective Lagrangian approach. This model encompasses the excitation of intermediate states leading to the production of $Δ(1920)$ through $π^{+}$ and $K^{+}$ meson exchanges between the initial $Σ^{+}$ baryon and the initial proton $p$, as well as the generation of $Δ(1940)$ via $π^{+}$ and $ρ^{+}$ meson exchanges. We provide predictions for the total and differential cross sections and discuss the potential impacts of cutoff parameters, off-shell effects, and branching ratios on the $Δ^{\ast} \to a_0 p$ decay. Given the dominance of $Δ(1940)$ in the region close to the reaction threshold, this reaction is considered an ideal platform for deeply exploring the unique properties of the $Δ(1940)$ resonance. Through this approach, we can gain a more precise understanding of the intrinsic characteristics of this particle.

hep-ph↗

arXiv2024

Incommensurate magnetic order in an axion insulator candidate EuIn$_2$As$_2$ investigated by NMR measurement

Magnetic topological insulators exhibit unique electronic states due to the interplay between the electronic topology and the spin structure. The antiferromagnetic metal $\rm{EuIn_2As_2}$ is a prominent candidate material in which exotic topological phases, including an axion insulating state, are theoretically predicted depending on the magnetic structure of the $\rm{Eu}^{2+}$ moments. Here, we report experimental results of the nuclear magnetic resonance (NMR) measurements of all the nuclei in $\rm{EuIn_2As_2}$ to investigate the coupling between the magnetic moments in the Eu ions and the conduction electrons in $\rm{In_2As_2}$ layers and the magnetic structure. The $^{75}\rm{As}$ and $^{115}\rm{In}$ NMR spectra observed at zero external magnetic field reveal the appearance of internal fields of $4.9$ and $3.6\ \rm{T}$ respectively at the lowest temperature, suggesting a strong coupling between the conduction electrons in the $\rm{In_2As_2}$ layer and the ordered magnetic moments in the Eu ions. The $^{75}\rm{As}$ NMR spectra under in-plane external magnetic fields show broad distributions of the internal fields produced by an incommensurate fan-like spin structure which turns into a forced ferromagnetic state above $0.7\ \rm{T}$. We propose a spin reorientation process that an incommensurate helical state at zero external magnetic field quickly changes into a fan state by applying a slight magnetic field.

cond-mat.str-el↗

arXiv2024

Exploring the molecular scenario of X(4160)

In this work, we investigate the decays of meson $X(4160)$ in the molecular frame. By using an effective lagrangian approach, we calculate the widths of $X(4160)\to J/ψϕ$, $D^*\bar{D}^*$, $D^*\bar{D}$ and $D\bar{D}$ through the triangle loop mechanism in the molecular scenario. Based on the compositeness condition, the coupling between $X(4160)$ and the $D_s^*\bar{D}_s^*$ molecular state is determined. The other coupling constants used are determined phenomenologically. The calculation of the decay widths shows that the $D^*\bar{D}^*$ decay mode has a larger branching ratio. These predictions can be seen as a test for the charmonium assignment of $X(4160)$.

hep-ph↗

arXiv2024

The Theoretical Study of $π^+p\to pa_0^+ϕ$ Reaction

We study the production of hyperon resonances in the $π^+p\to pa_0^+ϕ$ reaction within an effective Lagrangian approach. The model includes the production of $Δ(1940)$ and $Δ(1920)$ in the intermediate state excited by the $ρ$ and $p$ exchanges between the initial proton and $π$ meson. Due to the large contribution of $ρ$ exchange in $Δ(1940)$ production, $Δ(1940)$ is found a significant contribution near the threshold in this reaction. We provide total and differential cross section predictions for the reation and discuss the possible influence of model parameters, off-shell effects and branching ratios for $Δ(1940)\to pa_0$ and $Δ(1920)\to pa_0$ decays, which will be useful in future experimental studies. This reaction can provide a platform for studying the features of $Δ(1940)$ resonance, especially the coupling to $pa_0$ channel.

hep-ph↗

arXiv2024

Roles of the Narrow Electronic Band near the Fermi Level in 1T-TaS$_2$-Related Layered Materials

Here we use low-temperature scanning tunneling microscopy and spectroscopy (STM/STS) to reveal the roles of the narrow electronic band in two 1T-TaS$_2$-related materials (bulk 1T-TaS$_2$ and 4Hb-TaS$_2$). 4Hb-TaS$_2$ is a superconducting compound with alternating 1T-TaS$_2$ and 1H-TaS$_2$ layers, where the 1H-TaS$_2$ layer has weak charge density wave (CDW) pattern and reduces the CDW coupling between the adjacent 1T-TaS$_2$ layers. In the 1T-TaS$_2$ layer of 4Hb-TaS$_2$, we observe a narrow electronic band located near Fermi level, and its spatial distribution is consistent with the tight-binding calculations for two-dimensional 1T-TaS$_2$ layers. The weak electronic hybridization between the 1T-TaS$_2$ and 1H-TaS$_2$ layers in 4Hb-TaS$_2$ shifts the narrow electronic band to be slightly above the Fermi level, which suppresses the electronic correlation induced band splitting. In contrast, in bulk 1T-TaS$_2$, there is an interlayer CDW coupling induced insulating gap. In comparison with the spatial distributions of the electronic states in bulk 1T-TaS$_2$ and 4Hb-TaS$_2$, the insulating gap in bulk 1T-TaS$_2$ results from the formation of a bonding band and an antibonding band due to the overlap of the narrow electronic bands in the dimerized 1T-TaS$_2$ layers.

cond-mat.mes-hall↗

arXiv2024

Bot or Human? Detecting ChatGPT Imposters with A Single Question

Large language models (LLMs) like GPT-4 have recently demonstrated impressive capabilities in natural language understanding and generation. However, there is a concern that they can be misused for malicious purposes, such as fraud or denial-of-service attacks. Therefore, it is crucial to develop methods for detecting whether the party involved in a conversation is a bot or a human. In this paper, we propose a framework named FLAIR, Finding Large Language Model Authenticity via a Single Inquiry and Response, to detect conversational bots in an online manner. Specifically, we target a single question scenario that can effectively differentiate human users from bots. The questions are divided into two categories: those that are easy for humans but difficult for bots (e.g., counting, substitution, searching, and ASCII art reasoning), and those that are easy for bots but difficult for humans (e.g., memorization and computation). Our approach shows different strengths of these questions in their effectiveness, providing a new way for online service providers to protect themselves against nefarious activities. Our code and question set are available at https://github.com/hongwang600/FLAIR.

cs.CL↗

arXiv2024

Single spin asymmetry $ A _{ U L } ^ { \sin ( 2 ϕ_ { h } ) }$ in dihadron production in SIDIS

The paper calculates the helicity-dependent dihadron fragmentation function (DiFF), by extending the dihadron spectator model and examine the single longitudinal spin asymmetry $A^{\sin(2ϕ_h)}_{UL}$ from dihadron in semi-inclusive inelastic scattering (SIDIS). This function elucidates the relationship between the longitudinal polarization of the fragmented quark and the transverse momentum of the resulting hadron pairs. A study by the COMPASS collaboration detected a minimal signal in their experimental search for this azimuthal asymmetry in SIDIS. Here, we use the spectator model to calculate the unknown T-odd dihadron fragmentation function $H_1^\perp$. Adopting collinear factorization to describe the data, avoiding the transverse momentum dependent factorization and the associated resummation effects, helping us understand the asymmetry and explaining why the signal is so weak. We involve the approach of transverse momentum dependence in the model calculations, in order to formulate the differential cross sections and the spin asymmetries in terms of the collinear parton distributions and the collinear DiFFs. A transverse momentum factor analysis method was used, in which the transverse momentum of the final hadron pairs was not integrated. The asymmetry of $sin(2ϕ_h)$ in COMPASS kinematics was calculated and compared with experimental data. In addition, predictions for the same asymmetry are also presented for HERMES and the Electron Ion Collider.

hep-ph↗

arXiv2024

Doping-tunable Fermi surface with persistent topological Hall effect in axion candidate EuIn$_2$As$_2$

Rare-earth Zintl compound EuIn$_2$As$_2$ has been theoretically recognized as a candidate for realizing an intrinsic antiferromagnetic (AFM) bulk axion insulator and a higher-order topological state, which provides a fertile platform to explore novel topological transport phenomena. However, the axion state has yet to be realized because EuIn$_2$As$_2$ is highly hole-doped. Here, we synthesized a series of high-quality Ca-doped EuIn2As2 (Ca$_x$Eu$_{1-x}$In$_2$As$_2$, x = 0 ~ 0.25) single crystals to tune the Fermi energy above the hole pocket. Our Hall measurements reveal that the isovalent Ca substitution decreases the hole carrier density by shrinking the lattice spacing, which is also confirmed by our first-principles calculations. We further find that both the temperature dependence of the magnetic susceptibility with a local maximum at the Néel temperature and the topological Hall effect originating from the finite real-space spin chirality persist in the Ca-doped samples as observed in the pristine EuIn$_2$As$_2$, despite that the nonmagnetic Ca substitution decreases the effective moment and the Néel temperature. These results show that the Ca substitution tunes the Fermi energy while keeping the AFM magnetic structure, suggesting that the axion insulating state may be realized by further Ca substitution.

cond-mat.mtrl-sci↗

arXiv2024

Learning 1D Causal Visual Representation with De-focus Attention Networks

Modality differences have led to the development of heterogeneous architectures for vision and language models. While images typically require 2D non-causal modeling, texts utilize 1D causal modeling. This distinction poses significant challenges in constructing unified multi-modal models. This paper explores the feasibility of representing images using 1D causal modeling. We identify an "over-focus" issue in existing 1D causal vision models, where attention overly concentrates on a small proportion of visual tokens. The issue of "over-focus" hinders the model's ability to extract diverse visual features and to receive effective gradients for optimization. To address this, we propose De-focus Attention Networks, which employ learnable bandpass filters to create varied attention patterns. During training, large and scheduled drop path rates, and an auxiliary loss on globally pooled features for global understanding tasks are introduced. These two strategies encourage the model to attend to a broader range of tokens and enhance network optimization. Extensive experiments validate the efficacy of our approach, demonstrating that 1D causal visual representation can perform comparably to 2D non-causal representation in tasks such as global perception, dense prediction, and multi-modal understanding. Code is released at https://github.com/OpenGVLab/De-focus-Attention-Networks.

cs.CV↗

arXiv2024

Theoretical study of the $B^+\to D^-D_s^{+}π^+$ reaction

Prompted by the recent discoveries of $T_{c\bar{s}0}(2900)^{++}$ in the $D_s^+π^+$ invariant mass distribution of $B^+\to D^-D_s^+π^+$ process, we present a model that hopes to help us investigate the nature of $T_{c\bar{s}0}(2900)^{++}$ by reproducing the mass distribution of $D^-π^+, D_s^+π^+$ and $D^-D_s^+$ in $B^+ \to D^-D_s^+π^+$ decays. The structure of the triangular singularity peak generated from the $χ_{c1}D^{*+}K^{*+}$ loop near the $D^{*+}K^{*+}$ threshold is considered in our model may be the experimentally discovered resonance-like state structure $T_{c\bar{s}0}(2900)^{++}$. In addition, we employ a coupled-channel approach to describe the dominant contribution of the $Dπ$ $S\text{-wave}$ amplitude, and also consider other excitations. Our model provides a well fit to the invariant mass distributions of $D^-π^+, D_s^+π^+$ and $D^-D_s^+$ simultaneously.

hep-ph↗

arXiv2023

Pole determination of $X(3960)$ and $X_0(4140)$ in decay $B^+\to K^+D_s^+D_s^-$

Two near-threshold peaking structures with spin-parities $J^{PC}=0^{++}$ were recently discovered by the LHCb Collaboration in the $D_s^+D_s^-$ invariant mass distribution of the decay process $B^+\to D_s^+D_s^-K^+$. In our study, we employed a coupled-channel model to fit the experimental results published by the LHCb collaboration, simultaneously fitting the model to the invariant mass distributions of $M_{D_s^+D_s^-}$, $M_{D_s^+K^+}$, and $M_{D_s^-K^+}$. We utilized a coupled-channel model to search for the poles of $X(3960)$ and $X_0(4140)$. The determination of the poles is meaningful in itself, and it also lays an foundation for the future research on $X(3960)$ and $X_0(4140)$. Upon turning off the coupled-channel and performing another fit, we observed a change in the fitting quality, the effect was almost entirely due to the peak of $X(3960)$, so we suggest that $X(3960)$ may not be a kinematic effect.

hep-ph↗

arXiv2023

Further study on the production of P-wave doubly heavy baryons from Z-boson decays

In this paper, we carried out a systematic investigation for the excited doubly heavy baryons production in $Z$-boson decays within the NRQCD factorization approach. Our investigation accounts for all the $P$-wave intermediate diquark states, {\it i.e.} $\langle cc\rangle[^1P_1]_{\bar 3}$, $\langle cc\rangle[^3P_J]_{6}$, $\langle bc\rangle[^1P_1]_{\bar 3/6}$, $\langle bc\rangle[^3P_J]_{\bar 3/6}$, $\langle bb\rangle[^1P_1]_{\bar 3}$, and $\langle bb\rangle[^3P_J]_{6}$ with $J = (0, 1, 2)$. The results show that contributions from all diquark states in $P$-wave were $7\%$, $8\%$, and $3\%$ in comparing with $S$-wave for the production of $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ via $Z$-boson decay, respectively. Based on these results, we predicted about $0.539\times 10^3(10^6)$ events for $Ξ_{cc}$, $1.827\times 10^3(10^6)$ events for $Ξ_{bc}$, and $0.036\times 10^3(10^6)$ events for $Ξ_{bb}$ can be produced annually at the LHC (CEPC). Additionally, we plot the differential decay widths of $Ξ_{cc}$, $Ξ_{bc}$ and $Ξ_{bb}$ as a function of the invariant mass $s_{23}$ and energy function $z$ distributions, and analyze the theoretical uncertainties in decay width arising from the mass parameters of heavy quark.

hep-ph↗

arXiv2023

Memory efficient location recommendation through proximity-aware representation

Sequential location recommendation plays a huge role in modern life, which can enhance user experience, bring more profit to businesses and assist in government administration. Although methods for location recommendation have evolved significantly thanks to the development of recommendation systems, there is still limited utilization of geographic information, along with the ongoing challenge of addressing data sparsity. In response, we introduce a Proximity-aware based region representation for Sequential Recommendation (PASR for short), built upon the Self-Attention Network architecture. We tackle the sparsity issue through a novel loss function employing importance sampling, which emphasizes informative negative samples during optimization. Moreover, PASR enhances the integration of geographic information by employing a self-attention-based geography encoder to the hierarchical grid and proximity grid at each GPS point. To further leverage geographic information, we utilize the proximity-aware negative samplers to enhance the quality of negative samples. We conducted evaluations using three real-world Location-Based Social Networking (LBSN) datasets, demonstrating that PASR surpasses state-of-the-art sequential location recommendation methods

cs.AI↗

arXiv2023

Investigating $D_s^+ \to π^0 \ell^+ ν_\ell$ decay process within QCD sum rule approach

In this paper, the semileptonic decays $D_s^+ \to π^0\ell^+ ν_\ell$ with $\ell=(e,μ)$ are investigated by using the light-cone sum rule approach. Firstly, the neutral meson mixing scheme between $π^0$, $η$, $η^\prime$ and pseudoscalar gluonium $G$ is discussed in a unified way, which leads to the direct connection between two different channels for $D_s^+\to π^0\ell^+ν_\ell$ and $D_s^+ \to η\ell^+ν_\ell$ by the $π^0-η$ mixing angle. Then we calculated the $D_s\to π^0$ transition form factors (TFFs) within QCD light-cone sum rule approach up to next-to-leading order correction. At the large recoil point, we have $f_+^{D_s^+π^0}(0)=0.0113_{-0.0019}^{+0.0024}$ and $f_-^{D_s^+π^0}(0)=0.0020_{-0.0009}^{+0.0008}$. Furthermore, the TFFs are extrapolated to the whole physical $q^2$-region by using the simplified $z(q^2)$-series expansion. The behaviors of TFFs and related three angular coefficient functions $a_{θ_\ell}(q^2)$, $b_{θ_\ell}(q^2)$ and $c_{θ_\ell}(q^2)$ are given. The differential decay widths for $D_s^+ \to π^0\ell^+ ν_\ell$ with respect to $q^2$ and $\cosθ_\ell$ are presented, and also lead to the branching fractions ${\cal B}(D_s^+\to π^0e^+ν_e) =2.60_{-0.51}^{+0.57}\times 10^{-5}$ and ${\cal B}(D_s^+\to π^0μ^+ν_μ)= 2.58_{-0.51}^{+0.56}\times 10^{-5}$. These results show well agreement with the recent BESIII measurements and theoretical predictions. Then the differential distributions and integrated predictions for three angular observables, {\it i.e.} forward-backward asymmetries, $q^2$-differential flat terms and lepton polarization asymmetries are given separately. Lastly, we estimate the ratio for different decay channels ${\cal R}_{π^0/η}^{\ell}=1.108_{-0.071}^{+0.039}\times 10^{-3}$.

hep-ph↗

arXiv2023

Comprehensive investigation of Quantum Oscillations in Semimetal Using an ac Composite Magnetoelectric Technique with Ultrahigh Sensitivity

Quantum oscillation (QO), a physical phenomenon that reflects the characteristics of the Fermi surface and transport fermions, has been extensively observed in metals and semimetals through various approaches, like magnetostriction, magnetization, resistivity, and thermoelectric power. However, only some allowed oscillation frequencies can be revealed by each individual method, particularly in semimetals with intricate Fermi pockets and associated magnetic breakdown phenomena. In this paper, we present the application of an ac composite magnetoelectric (ME) technique to measure the QOs of a topological nodal-line semimetal, ZrSiS, which possesses six fundamental QO frequencies. By employing the ME technique with a maximum magnetic field of 13 T and a minimum temperature of 2 K, we are able to capture all the fundamental frequencies and most of the permissible magnetic breakdown frequencies. In comparison, some of the frequencies were missing in the aforementioned four methods under identical measurement conditions. Remarkably, a series of magnetic breakdown frequencies around 8000 T were revealed even in a magnetic field as low as 7.5 T. These findings highlight the ME technique as an ultrahigh-sensitive tool for studying Dirac Fermions and other topological semimetals with complex Fermi surfaces.

cond-mat.str-el↗

arXiv2023

STOA-VLP: Spatial-Temporal Modeling of Object and Action for Video-Language Pre-training

Although large-scale video-language pre-training models, which usually build a global alignment between the video and the text, have achieved remarkable progress on various downstream tasks, the idea of adopting fine-grained information during the pre-training stage is not well explored. In this work, we propose STOA-VLP, a pre-training framework that jointly models object and action information across spatial and temporal dimensions. More specifically, the model regards object trajectories across frames and multiple action features from the video as fine-grained features. Besides, We design two auxiliary tasks to better incorporate both kinds of information into the pre-training process of the video-language model. The first is the dynamic object-text alignment task, which builds a better connection between object trajectories and the relevant noun tokens. The second is the spatial-temporal action set prediction, which guides the model to generate consistent action features by predicting actions found in the text. Extensive experiments on three downstream tasks (video captioning, text-video retrieval, and video question answering) demonstrate the effectiveness of our proposed STOA-VLP (e.g. 3.7 Rouge-L improvements on MSR-VTT video captioning benchmark, 2.9% accuracy improvements on MSVD video question answering benchmark, compared to previous approaches).

cs.CV↗

arXiv2023

Observation of spin-polarized surface states in a nodal line semimetal SnTaS$_{2}$

The superconductor SnTaS$_{2}$ is theoretically predicted to be an intriguing topological nodal line semimetal without consideration of spin-orbit coupling. By carrying out angle-resolved photoemission (ARPES) and spin-resolved ARPES measurements combined with band structure calculations, we have provided a complete picture of the electronic structure and spin polarization property for the prominent surface states of SnTaS$_{2}$. The low-energy electronic states are dominated by surface states; two of them are from the S-terminated surface, while four of them are from the Sn-terminated surface. These give rise to interesting Fermi surface topology of SnTaS$_{2}$: three pockets located at $\barΓ$, $\bar{M}$ and $\bar{K}$ for the S-terminated surface and two pockets surrounding $\barΓ$ and $\bar{K}$ for the Sn-terminated surface. We further reveal that two surface states that cross the Fermi level are spin-polarized. Since SnTaS$_{2}$ is also a superconductor, our observations indicate that it may provide a new platform to explore topological superconductivity and other exotic properties.

cond-mat.supr-con↗

arXiv2023

The theoretical study of $D_s^+\toπ^+π^0π^0$

Inspired by recent BESIII's amplitude analysis on $D_s^+\toπ^+π^0π^0$, we develop a model based on the chiral unitary approach to discribe the $D_s^+\toπ^+π^0π^0$ decay, where $D_s^+$ decays into a $π^+$ and a quark-antiquark pair through weak decay of charm quark. The interaction of pseudoscalar mesons produced by the hadronization of quark-antiquark pair will lead to dynamically generated $f_0(980)$. The dominant amplitudes from resonances $f_0(1370)$ and $f_2(1270)$ in BESIII fit are also included in our model. In addition to above contributions, to obtain a good fit we also add a amplitude from resonance $f_2(1430)$ to our model. Our model fits well $M_{π^0π^0}$ and $M_{π^+π^0}$ invariant mass distributions simultaneously.

hep-ph↗