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Xiang Liu

Publications and source records attributed to Xiang Liu.

At least 271 records · Page 15Linked to original sources
arXiv2023

Second-order optimality conditions for bilevel programs

Second-order optimality conditions of the bilevel programming problems are dependent on the second-order directional derivatives of the value functions or the solution mappings of the lower level problems under some regular conditions, which can not be calculated or evaluated. To overcome this difficulty, we propose the notion of the bi-local solution. Under the Jacobian uniqueness conditions for the lower level problem, we prove that the bi-local solution is a local minimizer of some one-level minimization problem. Basing on this property, the first-order necessary optimality conditions and second-order necessary and sufficient optimality conditions for the bi-local optimal solution of a given bilevel program are established. The second-order optimality conditions proposed here only involve second-order derivatives of the defining functions of the bilevel problem. The second-order sufficient optimality conditions are used to derive the Q-linear convergence rate of the classical augmented Lagrangian method.

math.OC↗
arXiv2023

Observational constraint on Dark Energy from Quantum Uncertainty

We explore the theoretical possibility that dark energy density is derived from the vacuum particle pairs together with the quantum fluctuation of space-time. By assuming the vacuum particle pairs fall into the horizon boundary of the cosmos with the expansion of the universe, we can deduce the uncertainty in the relative position of particle pairs based on the quantum fluctuation of space-time, which can be used to estimate their or dark energy density. Furthermore, we attempt to explain the origin of negative pressure from the increasing entropy density of the Boltzmann system and derive the equation for the state parameter, which is consistent with the specific equations of state for dark energy. Finally, we fit the models to the SNIa Pantheon sample and Planck 2018 CMB angular power spectra and give statistical results for the cosmology parameters.

gr-qc↗
arXiv2023

Investigating the spectroscopy behavior of undetected $1F$-wave charmed baryons

In this work, we investigate the spectroscopic properties of $1F$-wave charmed baryons, which have not yet been observed in experiments. We employ a non-relativistic potential model and utilize the Gaussian expansion method to obtain the mass spectra of these charmed baryons. Additionally, we focus on the two-body Okubo-Zweig-Iizuka allowed strong decay behaviors, which plays a crucial role in characterizing the properties of these baryons. Our comprehensive analyses of the mass spectra and two-body Okubo-Zweig-Iizuka allowed decay behaviors provides valuable insights for future experimental investigations. This study significantly contributes to our understandings of the spectroscopic properties of $1F$-wave charmed baryons.

hep-ph↗
arXiv2023

The reconstruction of dark energy with Ridge Regression Approach

It may be determined by non-parametric method if the dark energy evolves with time. We propose a method of combining PCA and biased estimation on the basis of ridge regression analysis to reconstruct parameters, meanwhile we present an interesting principal component selection criterion to avoid the arbitrariness of principal component selections, and use numerical integral by Lagrange interpolation to linearize the luminosity distance integral formula in nearly flat space to avoid instability of derivative for functional data. We get the preliminary test results that shows if $Δ\overline w (z) = \overline {\left| {1 + w(z)} \right|} <=0.05$ included $w(z) = -1$, the probability of making a type I error for ${w_{recon}} \ne -1$ is almost zero ($1\% $) in the test; otherwise, if $Δ\overline w (z) = \overline {\left| {1 + w(z)} \right|} > 0.05$, the probability of making a type I error for ${w_{recon}} = -1$ is not more than $10\% $. Finally, we use JLA sample to reconstruct $w(z)$, and the results reject ${\rm{w(z) }} \ne {\rm{ - 1}}$, which is agreement with $ΛCDM$ model.

astro-ph.CO↗
arXiv2023

Exploring kaon induced reactions for unraveling the nature of the scalar meson $a_0 (1817)$

In this study, we comprehensively investigate the production of isovector scalar meson $a_{0}(1817)$ using the effective Lagrangian approach. Specifically, we employ the Reggeized $t$ channel Born term to calculate the total and differential cross sections for the reaction $K^{-}p \rightarrow a_{0}(1817)Λ$. Our analysis reveals that the optimal energy range for detecting the $a_{0}(1817)$ meson lies between $W=3.4$ GeV and $W=3.6$ GeV, where the predicted total cross section reaches a minimum value of 112 nb. Notably, the $t$ channel, as predicted by the Regge model, significantly enhances the differential cross sections, particularly at extreme forward angles. Furthermore, we investigate the Dalitz processes of $2\rightarrow 3$ and discuss the feasibility of detecting the $a_{0}(1817)$ meson in experiments such as J-PARC.

hep-ph↗
arXiv2023

Torsion Graph Neural Networks

Geometric deep learning (GDL) models have demonstrated a great potential for the analysis of non-Euclidian data. They are developed to incorporate the geometric and topological information of non-Euclidian data into the end-to-end deep learning architectures. Motivated by the recent success of discrete Ricci curvature in graph neural network (GNNs), we propose TorGNN, an analytic Torsion enhanced Graph Neural Network model. The essential idea is to characterize graph local structures with an analytic torsion based weight formula. Mathematically, analytic torsion is a topological invariant that can distinguish spaces which are homotopy equivalent but not homeomorphic. In our TorGNN, for each edge, a corresponding local simplicial complex is identified, then the analytic torsion (for this local simplicial complex) is calculated, and further used as a weight (for this edge) in message-passing process. Our TorGNN model is validated on link prediction tasks from sixteen different types of networks and node classification tasks from three types of networks. It has been found that our TorGNN can achieve superior performance on both tasks, and outperform various state-of-the-art models. This demonstrates that analytic torsion is a highly efficient topological invariant in the characterization of graph structures and can significantly boost the performance of GNNs.

cs.LG↗
arXiv2023

Radiative decays and magnetic moments of the predicted $B_c$-like molecules

In this work, we first perform a systematic study of the transition magnetic moments and the corresponding radiative decay behaviors of the $B_c$-like molecular states associated with their mass spectra, where the constituent quark model is adopted by considering the $S$-$D$ wave mixing effect. Our numerical results show that the radiative decay properties can be considered as the effective physical observable to reflect the inner structures of these $B_c$-like molecular states. Meanwhile, we also discuss the magnetic moments of the $B_c$-like molecular states, and we find that the magnetic moment properties can be used to distinguish the $B_c$-like molecular states from the conventional $B_c$ mesonic states, which have the same quantum numbers and similar masses. We expect that the present study can inspire the interest of the experimentalist in exploring the electromagnetic properties of the $B_c$-like molecular states, especially the radiative decay properties.

hep-ph↗
arXiv2023

Unveiling the small-scale jets in the rapidly growing supermassive black hole IZw1

Accretion of black holes at near-Eddington or super-Eddington rates is the most powerful episode that drives black hole growth, and it may work in several types of objects. However, the physics of accretion and jet-disc coupling in such a state remains unclear, mainly because the associated jets are not easily detectable due to the extremely weak emission or possibly episodic nature of the jets. Only a few near/super-Eddington systems have demonstrated radio activity, and it remains unclear whether there is a jet and what are their properties, in super-Eddington active galactic nuclei (AGNs) (and ultraluminous X-ray sources). The deficit is mainly due to the complex radio mixing between the origins of jets and others, such as star formation activity, photo-ionized gas, accretion disk wind, and coronal activity. In this work, we conducted high-resolution very long baseline interferometry (VLBI) observations to explore the jets in the highly accreting narrow-line Seyfert I system IZw1. Our observations successfully revealed small-scale jets (with a linear size of $\sim45$ parsec) at both 1.5 and 5 GHz, based on the high radio brightness temperature, radio morphology, and spectral index distribution. Interestingly, the lack of a flat-spectrum radio core and knotty jet structures imply episodic ejections in IZw1, which resemble the ejection process in Galactic X-ray binaries that are in the canonical very high state. The high accretion rates and jet properties in the AGN IZw1 may support the AGN/XRB analogy in the extreme state.

astro-ph.HE↗
arXiv2023

How dark the sky: the JWST backgrounds

We describe the sources of stray light and thermal background that affect JWST observations, report actual backgrounds as measured from commissioning and early-science observations, compare these background levels to prelaunch predictions, estimate the impact of the backgrounds on science performance, and explore how the backgrounds probe the achieved configuration of the deployed observatory. We find that for almost all applications, the observatory is limited by the irreducible astrophysical backgrounds, rather than scattered stray light and thermal self-emission, for all wavelengths lambda < 12.5 micron, thus meeting the level 1 requirement. This result was not assured given the open architecture and thermal challenges of JWST, and it is the result of meticulous attention to stray light and thermal issues in the design, construction, integration, and test phases. From background considerations alone, JWST will require less integration time in the near-infrared compared to a system that just met the stray-light requirements; as such, JWST will be even more powerful than expected for deep imaging at 1-5 micron. In the mid-infrared, the measured thermal backgrounds closely match prelaunch predictions. The background near 10 micron is slightly higher than predicted before launch, but the impact on observations is mitigated by the excellent throughput of MIRI, such that instrument sensitivity will be as good as expected prelaunch. These measured background levels are fully compatible with JWST's science goals and the Cycle 1 science program currently underway.

astro-ph.IM↗
arXiv2023

Doubly charmed dibaryon states

In this work, we study the doubly charmed dibaryon states with the $qqqqcc$ ($q =u, d, s$) configuration. The mass spectra of doubly charmed dibaryon states are obtained systematically within the chromomagnetic interaction model. In addition to the mass spectrum analysis, we illustrate their two-body strong decay behaviours. Our results suggest that there may be narrow states or even stable states that cannot decay through the strong interaction. We hope that our results will provide valuable information for further experimental searches for doubly charmed dibaryon states.

hep-ph↗
arXiv2023

New reaction approach to reflect exotic structure of hadronic molecular state

With the accumulation of experimental data, more and more exotic hadrons are observed. Among the interpretations of these exotic hadrons, molecular state and compact multiquark are two of the most popular pictures. However, it is still difficult to determine the structure of an exotic hadron. In this work, we propose a possible way to detect the internal structure of an exotic state. When a molecular state composed of two consistent hadrons is attacked by another particle, one of the constituents should be kicked out while another quasifree constituent stays almost unaffected. It is different from a compact multiquark which has no obvious subcluster. In this work, taking the $X(3872)$ as an example, we perform a Dalitz plot analysis of such reaction to find the effect of the different internal structures. Under the assumption of the $X(3872)$ as a molecular state or a compact tetraquark state, with the help of the effective Lagrangians, the Dalitz plot and the invariant mass spectrum are estimated with different total invariant mass of three final particles, and the effect of different binding energies is also discussed. Obvious event concentration can be observed as strips in the Dalitz plot and sharp peaks in the invariant mass spectrum for the $X(3872)$ with a small binding energy under the molecular state picture, while such concentration cannot be observed under the compact tetraquark picture. Such phenomenon can be applied to identify the internal structure of a new hadron state.

hep-ph↗
arXiv2023

Toy model to understand oscillatory behavior in timelike nucleon form factors

To understand the oscillatory behavior exhibited in the timelike electromagnetic form factors of nucleons, we propose a toy model based on the Jost function of the $N\bar N$ pair into the timelike form factors with the help of the distorted-wave Born approximation. By constructing a simple square-well potential reflecting the final-state interaction of $N\bar N$, we naturally represent the damped oscillatory phenomenon in the timelike electromagnetic form factors of nucleons. Especially, our study reveals that the ``period" of the oscillation is approximately determined by the Yukawa interaction range $1/m_π$. Other possible potentials are also discussed. The threshold enhancements of the cross sections for $e^+e^-\to n\bar n$, $Λ\barΛ$, and $Λ_c\barΛ_c$ can also be understand within this scenario.

nucl-th↗
arXiv2023

Transition form factors and angular distributions of the $\bm{Λ_b\toΛ(1520)(\to N\bar{K})\ell^+\ell^-}$ decay supported by baryon spectroscopy

We calculate the weak transition form factors of the $Λ_b\toΛ(1520)$ transition, and further calculate the angular distributions of the rare decays $Λ_b\toΛ(1520)(\to N\bar{K})\ell^{+}\ell^{-}$ ($N\bar{K}=\{pK^-,n\bar{K}^0\}$) with unpolarized $Λ_b$ and massive leptons. The form factors are calculated by the three-body light-front quark model with the support of numerical wave functions of $Λ_b$ and $Λ(1520)$ from solving the semirelativistic potential model associated with the Gaussian expansion method. By fitting the mass spectrum of the observed single bottom and charmed baryons, the parameters of the potential model are fixed, so this strategy can avoid the uncertainties arising from the choice of a simple harmonic oscillator wave function of the baryons. With more data accumulated in the LHCb experiment, our result can help for exploring the $Λ_b\toΛ(1520)\ell^+\ell^-$ decay and deepen our understanding on the $b\to s\ell^+\ell^-$ processes.

hep-ph↗
arXiv2023

The newly observed $Ω_c(3327)$: A good candidate for a $D$-wave charmed baryon

The newly observed $Ω_c(3327)$ gives us a good chance to construct the $Ω_c$ charmed baryon family. In this work, we carry out the mass spectrum analysis by a non-relativistic potential model using Gaussian Expansion Method, and the study of its two-body Okubo-Zweig-Iizuka allowed strong decay behavior. Our results imply that the $Ω_c(3327)$ is good candidate of $Ω_c(1D)$ state with $J^P=5/2^+$. We also predict the spectroscopy behavior of other $Ω_c(1D)$ states, which may provide further clues to their search.

hep-ph↗
arXiv2023

Correlation analysis between several observables of OJ 287 radio jet

We collected the archival data of blazar OJ~287 from heterogeneous very long baseline interferometry (VLBI) monitoring programs at 2.3 GHz, 8.6 GHz, 15 GHz and 43 GHz. The data reduction and observable extraction of those multi-band multi-epoch observations are batch-processed consistently with our automated pipeline. We present the multivariate correlation analysis on the observables at each band. We employ the cross-correlation function to search the correlations and the Monte Carlo (MC) technique to verify the certainty of correlations. Several correlations are found. The foremost findings are the correlations between the core flux density and the jet position angles on different scales, which validated the plausible predictions of the jet with precession characteristics. Meanwhile, there is a variation in the offset between the core EVPA and the inner-jet position angle over time at 15~GHz and 43~GHz.

astro-ph.GA↗
arXiv2023

Confirming the existence of a new higher charmonium $ψ(4500)$ by the newly released data of $e^+e^- \to K^+K^- J/ψ$

Recently, the BESIII Collaboration published the Born cross section of $e^+e^- \to K^+K^- J/ψ$, in which a new vector enhancement structure $Y(4500)$ was observed for the first time. The mass of the $Y(4500)$ resonance structure is in good agreement with our previous prediction for a $5S$-$4D$ mixing charmonium candidate $ψ(4500)$, while the measured width is $2σ$ larger than the theoretical estimate. In this work, we reanalyzed the cross section of $e^+e^- \to K^+K^- J/ψ$ by introducing two theoretically predicted charmonium states $ψ(4220)$ and $ψ(4500)$ as intermediate resonances, and found that this width deviation problem can be resolved. Meanwhile, we found that the inclusion of two established charmonium states $ψ(4160)$ and $ψ(4415)$ can further improve the fit quality, with four sets of widely different solutions to $Γ_{e^+e^-} \mathcal{B}(ψ\to K^+K^- J/ψ)$. In order to better identify the properties of the $Y(4500)$, we calculated the charmonium hadronic transition to final states $K^+K^- J/ψ$ within the charmed meson loop mechanism, where the fitted branching ratio of $ψ(4500) \to K^+K^- J/ψ$ can be well explained by the theoretical calculation, further supporting the new enhancement structure around 4.5 GeV as a higher charmonium $ψ(4500)$ that we predicted. Finally, we also discussed the possible signal of another predicted charmonium candidate $ψ(4380)$ in $e^+e^- \to K^+K^- J/ψ$. These research results should be an important step in constructing the charmonium family and thoroughly solving the charmoniumlike $Y$ problem.

hep-ph↗
arXiv2023

New type of hydrogenlike charm-pion or charm-kaon matter

Borrowing the structures of the hydrogen atom, molecular ion, and diatomic molecule, we predict the nature of a new type of hydrogenlike charm-pion or charm-kaon matter that could be obtained by replacing the proton and electron in hydrogen matter with a charmed meson and a pion or a kaon, respectively. We find that the spectra of the atom, molecular ion, and diatomic molecule can be obtained simultaneously with the Coulomb potential for the hydrogen, the charm-pion, and the charm-kaon systems. The predicted charm-pion matter also allows us to explore the mass shift mediated by the strong interaction. For the charm-pion and charm-kaon systems, the strong interactions could lead to binding energy shifts. Our calculations suggests that the binding energy shifts in charm-pion systems are in the order of several to tens of eV. For the charm-kaon systems, the results are in the order of tens to hundreds of eV. Exploring hydrogenlike charm-pion matter must lead to new demands for high-precision experiments.

hep-ph↗
arXiv2023

A Sparse Graph-Structured Lasso Mixed Model for Genetic Association with Confounding Correction

While linear mixed model (LMM) has shown a competitive performance in correcting spurious associations raised by population stratification, family structures, and cryptic relatedness, more challenges are still to be addressed regarding the complex structure of genotypic and phenotypic data. For example, geneticists have discovered that some clusters of phenotypes are more co-expressed than others. Hence, a joint analysis that can utilize such relatedness information in a heterogeneous data set is crucial for genetic modeling. We proposed the sparse graph-structured linear mixed model (sGLMM) that can incorporate the relatedness information from traits in a dataset with confounding correction. Our method is capable of uncovering the genetic associations of a large number of phenotypes together while considering the relatedness of these phenotypes. Through extensive simulation experiments, we show that the proposed model outperforms other existing approaches and can model correlation from both population structure and shared signals. Further, we validate the effectiveness of sGLMM in the real-world genomic dataset on two different species from plants and humans. In Arabidopsis thaliana data, sGLMM behaves better than all other baseline models for 63.4% traits. We also discuss the potential causal genetic variation of Human Alzheimer's disease discovered by our model and justify some of the most important genetic loci.

cs.LG↗