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Zhi-Wei Liu

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eess.SY hep-ph nucl-th hep-ex Systems and Control hep-lat Machine Learning math.OC nucl-ex

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preprint2026arXiv

Learning to Sparsify Stochastic Linear Bandits

This paper addresses the problem of learning to sparsify stochastic linear bandits, where a decision-maker sequentially selects actions from a high-dimensional space subject to a sparsity constraint on the number of nonzero elements in the action vector. The key challenge lies in minimizing cumulative regret while tackling the potential NP-hardness of finding optimal sparse actions due to the inherent combinatorial structure of the problem. We propose an adaptively phased exploration and exploitation algorithmic framework, utilizing ordinary least squares for parameter learning and specialized subroutines for sparse action selection. When the action set is a Euclidean ball, optimal sparse actions can be efficiently computed, enabling us to establish a $\tilde{\mathcal{O}}(d\sqrt{T})$ regret, where $d$ is the dimension of the action vector and $T$ is the time horizon length. For general convex and compact action sets where finding optimal sparse actions is intractable, we employ a greedy subroutine. For general strongly convex action sets, we derive a $\tilde{\mathcal{O}}(d \sqrt{T})$ $α$ -regret; for general compact sets lacking strong convexity, we establish a $\tilde{\mathcal{O}}(d T^{2/3})$ $α$ -regret, where $α$ pertains to the approximation ratio of the greedy algorithm. Finally, we validate the performance of our algorithms using extensive experiments including an application to recommendation system.

preprint2025arXiv

$J/ψΛ$ femtoscopy and the nature of $P_{ψs}^Λ(4338)$

Over the past two decades, numerous exotic hadron states have been discovered, yet their underlying nature remains unclear. It is widely acknowledged that understanding hadron-hadron interactions is essential to unraveling their properties. Hadron spectroscopy is a powerful tool for this endeavor, providing rich experimental data that can shed light on exotic systems. Recently, the LHCb experiment analyzed the process $B^{-} \rightarrow J/ψΛ\bar{p}$ and observed a narrow peak in the $J/ψΛ$ invariant mass spectrum, regarding it as a candidate for a pentaquark. In this work, we extract the coupled-channel $J / ψΛ-\bar{D} Ξ_c-\bar{D}_s Λ_c$ potential based on the $J/ψΛ$ invariant mass spectrum. Our results indicate the existence of a bound state below the $\bar{D} Ξ_c$ mass threshold, corresponding to the experimentally measured state $P_{cs}(4338)$ . Furthermore, we predict the scattering lengths and momentum correlation functions for the $J/ψΛ$ and $\bar{D}Ξ_c$ channels, which serve as theoretical references for future femtoscopy experiments.

preprint2022arXiv

Prespecified-time observer-based distributed control of battery energy storage systems

This paper studies the state-of-charge (SoC) balancing and the total charging/discharging power tracking issues for battery energy storage systems (BESSs) with multiple distributed heterogeneous battery units. Different from the traditional cooperative control strategies based on the asymptotical or finite-time distributed observers, two distributed prespecified-time observers are proposed to estimate average battery units state and average desired power, respectively, which can be determined in advance and independent of initial states or control parameters. Finally, two simulation examples are given to verify the effectiveness and superiority of the proposed control strategy.

preprint2022arXiv

Test of the hyperon-nucleon interaction within leading order covariant chiral effective field theory

Motivated by the recent experimental measurements of differential cross sections of the $Σ^{-}p$ elastic scattering in the momentum range of $470$ to $850$ MeV $/c$ by the J-PARC E $40$ experiment, we extend our previous studies of $S=-1$ hyperon-nucleon interactions to relatively higher energies up to $900$ MeV $/c$ for both the coupled-channel $Λp\rightarrow(Λp, Σ^{+}n, Σ^{0}p)$ , $Σ^{-}p\rightarrow(Λn, Σ^{0}n, Σ^{-}p)$ and single-channel $Σ^{+}p\rightarrowΣ^{+}p$ reactions. We show that although the leading order covariant chiral effective field theory is only constrained by the low energy data, it can describe the high energy data reasonably well, in particular, the J-PARC E40 differential cross sections. The predicted cusp structure close to the $ΣN$ threshold in the $Λp\to Λp$ reaction agrees with the latest ALICE observation as well as with the results of the next-to-leading order heavy baryon chiral effective theory. On the other hand, the comparison with the latest CLAS data on the $Λp$ cross sections between 0.9 and 2.0 GeV $/c$ clearly indicates the need of higher order chiral potentials for such high momenta. This is also the case for the latest J-PARC data on the $Σp \rightarrow Λn$ differential cross sections. Nevertheless, even for these cases, the predictions are in qualitative agreement with the data, albeit with large uncertainties, implying that the predicted total and differential cross sections are of relevance for ongoing and planned experiments.

preprint2020arXiv

$Λ_c N$ interaction in leading order covariant chiral effective field theory

We study the $Λ_c N$ interaction in the covariant chiral effective field theory (ChEFT) at leading order. All the relevant low-energy constants are determined by fitting to the lattice QCD simulations from the HAL QCD Collaboration. Extrapolating the results to the physical point, we show that the $Λ_c N$ interaction is weakly attractive in the $^1S_0$ channel, but in the $^3S_1$ channel, it is only attractive at extremely low energies and soon turns repulsive for larger laboratory energy. Furthermore, we show that the neglect of the $^3S_1-{}^3D_1$ coupling provided by the leading order covariant ChEFT would result in an attractive interaction in the $^3S_1$ channel at the physical point, which coincides with the previous non-relatistic ChEFT study. As a byproduct, we predict the $^3D_1$ phase shifts and the mixing angel $\varepsilon_1$ , which can be checked by future lattice QCD simulations. In addition, we compare the $Λ_c N$ interaction with the $ΛN$ and $NN$ interactions to study how the baryon-nucleon ( $BN$ ) interactions evolve as a function of the baryon mass with the replacement of a light quark by a strange or charm quark in the baryon ( $B$ ).

preprint2020arXiv

Predefined-time Terminal Sliding Mode Control of Robot Manipulators

In this paper, we present a new terminal sliding mode control to achieve predefined-time stability of robot manipulators. The proposed control is developed based on a novel predefined-time terminal sliding mode (PTSM) surface, on which the states are forced to reach the origin in a predefined time, i.e., the settling time is independent to the initial condition and can be explicitly user-defined via adjusting some specific parameters called the predefined-time parameters. It is also demonstrated that the proposed control can provide satisfactory steady-state performance in the case of both external disturbances and parametric uncertainties. Besides, we present a formal systemic analysis method to derive the sufficient conditions for guaranteeing the predefined-time convergence of the closed-loop system. Finally, the effectiveness and performance of the presented control scheme are illustrated through both theoretical comparisons and numerical simulations.

preprint2020arXiv

Strangeness $S = -3$ and $-4$ baryon-baryon interactions in relativistic chiral effective field theory

The strangeness $S=-3$ and $-4$ baryon-baryon interactions are investigated in the relativistic chiral effective field theory at leading order. First, the potentials are derived from the $S=-1$ sector assuming that the corresponding low-energy constants are related to each other via SU(3) flavor symmetry. The comparison with the state-of-the-art lattice QCD simulations, show, however, that SU(3) flavor symmetry breaking effects can not be neglected. In order to take into account these effects, we redetermine two sets of low-energy constants by fitting to the lattice QCD data in the $ΞΣ$ and $ΞΞ$ channels respectively. The fitting results demonstrate that the lattice QCD $S$ -waves phase shifts for both channels can be described rather well. Without any additional free low-energy constants, the predicted phase shifts for the ${}^3D_1$ channel and the mixing angle $\varepsilon_1$ are also in qualitative agreement with the lattice QCD data for the $S=-3$ channel, while the results for the $S=-4$ channel remain to be checked by future lattice QCD simulations. With the so-obtained low-energy constants, the $S$ -wave scattering lengths and effective ranges are calculated for these two channels at the physical point. Finally, in combination with the $S=0$ and $-2$ results obtained in our previous works, we study the evolution of the irreducible representation $27$ in the baryon-baryon interactions as a function of increasing strangeness. It is shown that the attraction decreases dramatically as strangeness increases from $S=0$ to $S=-2$ , but then remains relatively stable until $S=-4$ . The results indicate that the existence of bound states in the $ΞΣ$ and $ΞΞ$ channels is rather unlikely.

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Zhi-Wei Liu

Research overview

Is this your work?

7 publications

Learning to Sparsify Stochastic Linear Bandits

$J/ψΛ$ femtoscopy and the nature of $P_{ψs}^Λ(4338)$

Prespecified-time observer-based distributed control of battery energy storage systems

Test of the hyperon-nucleon interaction within leading order covariant chiral effective field theory

$Λ_c N$ interaction in leading order covariant chiral effective field theory

Predefined-time Terminal Sliding Mode Control of Robot Manipulators

Strangeness $S = -3$ and $-4$ baryon-baryon interactions in relativistic chiral effective field theory

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Zhi-Wei Liu

Research overview

Is this your work?

7 publications

Learning to Sparsify Stochastic Linear Bandits

J/ψΛJ/ψΛJ/ψΛ femtoscopy and the nature of PψsΛ(4338)P_{ψs}^Λ(4338)PψsΛ​(4338)

Prespecified-time observer-based distributed control of battery energy storage systems

Test of the hyperon-nucleon interaction within leading order covariant chiral effective field theory

ΛcNΛ_c NΛc​N interaction in leading order covariant chiral effective field theory

Predefined-time Terminal Sliding Mode Control of Robot Manipulators

Strangeness S=−3S = -3S=−3 and −4-4−4 baryon-baryon interactions in relativistic chiral effective field theory

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Building this map preview

$J/ψΛ$ femtoscopy and the nature of $P_{ψs}^Λ(4338)$

$Λ_c N$ interaction in leading order covariant chiral effective field theory

Strangeness $S = -3$ and $-4$ baryon-baryon interactions in relativistic chiral effective field theory