arXiv subjects

Hua-Xing Chen

Publications and source records attributed to Hua-Xing Chen.

At least 19 recordsLinked to original sources

arXiv2026

Hadrons in group expansion

Various approximate symmetries exist in nature. For example, the flavor $SU(4)$ symmetry involving the $up/down/strange/charm$ quarks is severely broken, the flavor $SU(3)$ symmetry involving the $up/down/strange$ quarks is moderately broken, and the isospin $SU(2)$ symmetry involving the $up/down$ quarks is slightly broken. These broken symmetries are primarily governed by the strong interaction, making them an ideal platform for investigating the general behavior of approximate symmetries. To explore the application of the flavor $SU(4)$ group to ground-state baryons, we systematically calculate the transition matrices associated with various flavor $SU(4)$ representations as well as the matrices that describe their connections. These matrices are then employed to analyze the mass spectrum of ground-state baryons. Our results indicate that these states can be described as mixtures of various flavor representations, such as $Σ_c/Ξ_c^\prime/Ω_c \sim \mathbf{20_M} \oplus \mathbf{20_S}\oplus \mathbf{\bar{4}_A}~[SU(4)]$, $Ξ_c/Ξ_c^\prime \sim \mathbf{\bar 3_A} \oplus \mathbf{6_S}~[SU(3)]$, $Λ^0/Σ^0 \sim \mathbf{1_A} \oplus \mathbf{3_S}~[SU(2)]$, where the subscripts $\mathbf{S}$, $\mathbf{A}$, and $\mathbf{M}$ denote the symmetric, antisymmetric, and mixed flavor wave functions, respectively. Our results also indicate that the flavor symmetries, as they break, necessitate the mixing of these flavor representations according to specific rules. Together with a complementary analysis of vector mesons, these results motivate a general group-expansion picture in which the effective Hamiltonian evolves order by order as flavor symmetries are broken.

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arXiv2026

Quantum numbers of excited $Ξ_c^\prime$ and $Ω_c$ baryons and the $P$-wave $Σ_c$ spectrum

Recent precision measurements of excited heavy baryons, combined with systematic theoretical studies, make it possible to resolve the fine structure of their spectra. We calculate the masses and strong-decay properties of the $P$-wave charmed baryons using QCD sum rules and light-cone sum rules within heavy quark effective theory (HQET). Although seven states are allowed in each flavor sector, we find that only four $Σ_c$, four $Ξ_c^\prime$, and five $Ω_c$ states are expected to be experimentally resolvable. The similar mass-splitting patterns of $Ξ_c(2882)$, $Ξ_c(2923)$, $Ξ_c(2939)$, and $Ξ_c(2965)$ and of $Ω_c(3000)$, $Ω_c(3050)$, $Ω_c(3066)$, and $Ω_c(3090)$, together with our theoretical results, lead to the successive quantum-number assignments $J^P=1/2^-,3/2^-,3/2^-$, and $5/2^-$. We tentatively interpret $Ω_c(3119)$ as a predominantly $ρ$-mode excitation with $J^P=3/2^-$. We also predict the masses, widths, and dominant decay modes of four resolvable $P$-wave $Σ_c$ states, which may overlap within the observed $Σ_c(2800)$ and $Σ_c(2900)$ structures. Precision spectroscopy of the narrow $Ξ_c$ and $Ω_c$ states thus provides a route to resolving the $P$-wave $Σ_c$ spectrum.

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arXiv2026

Unified spectroscopy of $P$-wave flavor-sextet heavy baryons from QCD sum rules

We investigate the $P$-wave flavor-sextet charmed and bottom baryons within heavy quark effective theory. A key motivation is provided by the recent evidence for the $Ξ_c(2882)^0$, which completes a sequence of four narrow $Ξ_c$ structures together with the $Ξ_c(2923)^0$, $Ξ_c(2939)^0$, and $Ξ_c(2965)^0$. Their characteristic mass-splitting pattern closely parallels that of the $Ω_c(3000)^0$, $Ω_c(3050)^0$, $Ω_c(3066)^0$, and $Ω_c(3090)^0$ states, providing strong constraints on their spectroscopic assignments. We classify the seven $P$-wave states in each of the $Σ_Q$, $Ξ_Q^\prime$, and $Ω_Q$ sectors ($Q=c,b$), calculate their masses and intra-doublet mass splittings using QCD sum rules, and study their strong decays using light-cone sum rules. Configuration mixing between states with the same quantum numbers is also investigated. The combined analysis favors a common interpretation of the four narrow $Ξ_c$ and the four lowest narrow $Ω_c$ structures in terms of the corresponding $λ$-mode excitations. Extending the same framework to the bottom sector, we obtain a coherent picture of the observed $Σ_b$, $Ξ_b$, and $Ω_b$ structures. In particular, the $Σ_b(6097)$, $Ξ_b(6227)$, and $Ω_b(6350)$ structures may each contain an unresolved pair of nearby $P$-wave states. We also predict two additional $Σ_b$ states, two additional $Ξ_b^\prime$ states, and one additional $Ω_b$ state, all of which are expected to be relatively narrow and remain to be identified experimentally.

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arXiv2026

The decay properties of two- and three- gluon glueballs

We previously studied the decay properties of two- and three-gluon glueballs using the Fierz rearrangement method and obtained their relative branching ratios in Ref.~\cite{Tan:2026uue}. In this work, we extend and develop this analysis by providing a more complete treatment of two-gluon glueball decays and by considering the tensor and pseudotensor states with $J^{PC}=2^{++}$ and $2^{-+}$. We also perform an independent QCD sum rule analysis of the $0^{++}$ two-gluon glueball decay. The consistency between the two approaches provides a useful check of the Fierz analysis. Our results support a sizable gluon component in the $f_0(1710)$ and favor the $0^{-+}$ glueball interpretation of the $η(2370)$. For the tensor glueball, the vector--vector ($VV$) decay channels, especially $K^{*}(892)\bar{K}^{*}(892)$, are found to be favorable for experimental searches. We also study three-gluon glueballs with $J^{PC}=0^{++}$ and $1^{+-}$ and identify several potentially favorable three-meson decay channels, including $ππω$ and $K\bar Kϕ$. These results provide possible guidance for future experimental searches for glueball states.

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arXiv2026

Light tetraquark states with $J^{PC}=1^{--}$ from QCD sum rules

We perform a systematic QCD sum rule study of light tetraquark states with $J^{PC}=1^{--}$ in the diquark--antidiquark picture. A complete set of local interpolating currents is constructed and projected onto six flavor-isospin configurations ($q=u/d$): the isoscalar $q q\bar q\bar q$, $q s\bar q\bar s$, and $s s\bar s\bar s$ sectors, the isovector $q q\bar q\bar q$ and $q s\bar q\bar s$ sectors, and the isotensor $q q\bar q\bar q$ sector. The lowest masses in these sectors are derived to be $1.64^{+0.15}_{-0.14}$~GeV, $1.86^{+0.14}_{-0.14}$~GeV, $2.34^{+0.23}_{-0.30}$~GeV, $1.53^{+0.17}_{-0.19}$~GeV, $1.86^{+0.14}_{-0.14}$~GeV, and $2.24^{+0.12}_{-0.14}$~GeV, respectively. We further compare the present $1^{--}$ tetraquark spectrum with previous QCD sum rule results for the $1^{-+}$ tetraquark and hybrid states~\cite{Su:2025bhv}, aiming to provide useful information for distinguishing tetraquark and hybrid configurations in the light hadron spectrum. As an additional improvement, we complete the previously missing isotensor $1^{-+}$ tetraquark entry and obtain its lowest mass to be $M=2.19^{+0.26}_{-0.24}~\mathrm{GeV}$, which is included in the spectral comparison.

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arXiv2026

Subtraction of infrared divergences in light-quark QCD sum rules

In QCD sum rules for light-quark systems, infrared (IR) divergences can appear in the Wilson coefficients of certain condensates. These divergences manifest explicitly in the coordinate-space expressions of the light-quark propagators. We propose an improved method to eliminate these IR divergences at the propagator level and present a subtraction formula that implements this procedure. Compared to the existing methods that rely on the mixing between quark and gluon condensates of the same dimension to eliminate IR divergences, this method is more intuitive and easier to apply in practical QCD sum rule calculations.

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arXiv2026

New molecular bonds existing in the strong interaction

Similar to the covalent bond in chemical molecules induced by shared electrons, we proposed in [Commun. Theor. Phys. 74 (2022) 125201] the hadronic covalent bond induced by shared light quarks to explain the $T_{cc}(3875)$ and the deuteron. In this paper we improve and extend this mechanism to explain the $Z_c(3900)$, which is bound by the shared light quark-antiquark pair along with sea quark-antiquark pairs from the vacuum. Our analysis is based on the following forward and backward reasoning: a hadronic molecule exists, iff the attraction between its components is strong enough, iff the wave functions of its components significantly overlap with each other, iff the Pauli principle is well satisfied among all the shared quarks and antiquarks. Additionally, the $X(3872)$ is so unique that we need to further consider the annihilation of the shared light quark-antiquark pair, just in line with the reasoning that the creation and annihilation of sea quark-antiquark pairs should be given equal consideration. Both the creation and annihilation molecular bonds exist only in the strong interaction, not in the electromagnetic interaction, and they provide a quasi-static low-energy platform for studying the QCD confinement.

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arXiv2026

Fierz analyses on the decay properties of two- and three-gluon glueballs

The Fierz rearrangement, based on the various internal symmetries of hadrons, can be used to study their decay properties in a largely model-independent way. In this Letter we apply this method to calculate the relative branching ratios of two-gluon glueballs with $J^{PC} = 0^{++}/0^{-+}$ and three-gluon glueballs with $J^{PC} = 0^{++}/1^{+-}$. In total, we derive nearly one hundred ratios for these glueballs. Our results suggest that the $f_0(1710)$ and $η(2370)$ likely contain a significant gluon component, whereas the gluon component in $f_0(1500)$ appears to be small. Furthermore, we propose observing the three-gluon glueball with $J^{PC} = 0^{++}$ in the $ππω$ and $K\bar{K}ϕ$ channels, and the three-gluon glueball with $J^{PC} = 1^{+-}$ in the $ππω$, $ππϕ$, and $K\bar{K}ϕ$ channels. This study enhances our understanding of the gluonic structure of exotic hadrons and will assist future experimental searches in high-energy physics.

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arXiv2026

Investigations on heavy quarkonium hybrid mesons with exotic quantum numbers $J^{PC}=2^{+-}$

We investigate the heavy quarkonium hybrid mesons with exotic quantum numbers $J^{PC}=2^{+-}$ via QCD sum rule method. We construct the currents with three Lorentz indices and calculate the correlation functions up to dimension six at the leading order of $α_{s}$. The states with $J^{PC}=2^{+-}$ are extracted by constructing the corresponding projection operators. The obtained results indicate that the masses of $2^{+-}$ $\bar{c}Gc$ and $\bar{b}Gb$ hybrid states are about $4.49~\mathrm{GeV}$ and $10.48~\mathrm{GeV}$, respectively. We suggest to search for $\bar{c}Gc$ hybrid meson with $J^{PC}=2^{+-}$ in $J/ψf_{0,1,2}$ and $χ_{c0,1,2} ω$ final states.

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arXiv2026

Predictions of masses for light hybrid baryons

Within the method of parity-projected QCD sum rules, we study the mass spectra of light hybrid baryons with $I(J^{P})=1/2(1/2^{\pm}), 3/2(1/2^{\pm}), 1/2(3/2^{\pm}), 3/2(3/2^{\pm})$ by constructing the local $qqqg$ interpolating currents. We calculate the correlation functions up to dimension eight condensates at the leading order of $α_{s}$. The stable QCD Lapalce sum rules can be established for the positive-parity $N_{1/2^+}, Δ_{3/2^+}, Δ_{1/2^+}$ and negative-parity $N_{1/2^-}, N_{3/2^-}, Δ_{1/2^-}$ channels to extract their mass spectra. The lowest-lying hybrid baryons are predicted to be the positive-parity $N_{1/2^+}$ state around 2.01 GeV. These hybrid baryons mainly decay into conventional baryon plus meson final states. We propose to search for the light hybrid baryons through the $Υ/ψ(3686)$ decays via the three-gluon emission mechanism in BESIII and BelleII experiments. Hopefully our studies of the light hybrid baryons will be useful for understanding the excited baryon spectrum and the behavior of gluonic degrees of freedom in QCD.

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arXiv2025

Investigating charmed hybrid baryons via QCD sum rules

We investigate charmed hybrid baryons using the QCD sum rule method within the framework of heavy quark effective theory. We construct twenty-eight interpolating currents for charmed hybrid baryons, seven of which are employed in QCD sum rule analyses of nineteen states with quark-gluon configurations $qqcg$, $qscg$, and $sscg$ ($q = u/d$). The masses of the lowest-lying charmed hybrid baryons in the $SU(3)$ flavor $\mathbf{6}_F$ representation are calculated to be $M_{Σ_{cg}(1/2^+)} = 3.36^{+0.27}_{-0.26}~\rm{GeV}$, $M_{Ξ^\prime_{cg}(1/2^+)} = 3.59\pm 0.20~\rm{GeV}$, and $M_{Ω_{cg}(1/2^+)} = 3.82\pm 0.21~\rm{GeV}$. We propose that future experiments search for these states via their $P$-wave decay channels $ND^{(*)}$, $ΛD^{(*)}$, and $ΞD^{(*)}$, respectively. Such investigations would provide valuable insight into the role of gluonic excitations in hadron structure.

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arXiv2025

A short review on QCD sum rule studies of P-wave single heavy baryons

Over the past few decades, the study of singly heavy baryons has entered a golden era, with numerous excited states observed by experimental collaborations. Various theoretical approaches have been developed to investigate their properties, with the QCD sum rule method being one of the most widely applied. This paper provides a review of these QCD sum rule studies. Over the last ten years, we have systematically studied $P$-wave singly heavy baryons using QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. These $P$-wave singly heavy baryons can explain many excited heavy baryons, including the $Λ_c(2595)^+$, $Λ_c(2625)^+$, $Ξ_c(2790)^{0/+}$, $Ξ_c(2815)^{0/+}$, $Σ_c(2800)^0$, $Ξ_c(2882)^0$, $Ξ_c(2923)^0$, $Ξ_c(2939)^0$, $Ξ_c(2965)^0$, $Ω_c(3000)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, $Ω_c(3050)^0$, $Ω_c(3119)^0$, $Λ_b(5912)^0$, $Λ_b(5920)^0$, $Ξ_b(6087)^0$, $Ξ_b(6095)^0/Ξ_b(6100)^-$, $Σ_b(6097)^\pm$, $Ξ_b(6227)^-$, $Ω_b(6316)^-$, $Ω_b(6330)^-$, $Ω_b(6340)^-$, and $Ω_b(6350)^-$, etc. Furthermore, we predict additional $P$-wave singly heavy baryons, including two $Λ_b$ states, two $Ξ_b$ states, three $Σ_b$ states, three $Ξ_b^\prime$ states, two $Ω_b$ states, two $Λ_c$ states, two $Ξ_c$ states, three $Σ_c$ states, and one $Ω_c$ state, all with relatively narrow decay widths, making them viable candidates for experimental observation. The study of singly heavy baryons is closely related to two meaningful questions:"What is the shortest possible lifetime of an observable particle?" and "How can one generally describe approximate (flavor) symmetries?".

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arXiv2025

QCD sum rule study of topped mesons within heavy quark effective theory

Motivated by the recent CMS observation of a near-threshold enhancement in top quark pair production, we investigate a novel class of hadronic systems containing a single top quark: the topped mesons ($t\bar{q}$, with $\bar q = \bar u, \bar d, \bar s$). In contrast to the extensively studied toponium ($t\bar{t}$) system, analyzed primarily within perturbative QCD, topped mesons offer a complementary nonperturbative probe of QCD dynamics in the heavy quark limit. These states are expected to exhibit longer lifetimes and narrower decay widths than toponium, as only a single top quark undergoes weak decay. We employ QCD sum rules within the framework of heavy quark effective theory to study the structure and mass spectrum of ground-state topped mesons. Our analysis predicts masses near 173.1 GeV, approximately 0.5-0.6 GeV above the top quark pole mass. Compared with singly topped baryons ($tqq$, with $q = u, d, s$) studied concurrently in [arXiv:2507.05895], topped mesons have a simpler quark composition and more favorable decay channels (a topped meson is anticipated to decay weakly into a $Υ$ meson and a charmed meson), enhancing their potential for both theoretical analysis and experimental discovery.

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arXiv2025

QCD sum rule study on excited light meson operators

We apply the QCD sum rule method to systematically study excited light meson operators and calculate their decay constants. These operators are constructed by explicitly adding one covariant derivative to the quark-antiquark pair. In total, twelve such operators are constructed, among which ten are subjected to detailed numerical analyses. The considered quark contents include $\bar{q}q$, $\bar{q}s$, and $\bar{s}s$ ($q = u/d$), allowing the formation of various $SU(3)$ flavor nonets. For instance, our results support the interpretation that the $a_2(1320)$, $f_2(1270)$, $f_2^\prime(1525)$, and $K_2^*(1430)$ constitute a flavor nonet with quantum numbers $J^{P(C)} = 2^{+(+)}$. In addition, we predict several excited meson states, whose masses and decay constants are determined using the QCD sum rule method.

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arXiv2025

Improved prediction of the mass splitting for $P$-wave $Ω$ baryons

Using the QCD sum rule method, we investigate the mass splitting for the spin-orbit partner states of the $Ω(2012)$ baryon assuming that it is a $P$-wave excitation with $J^P=3/2^-$. This study is an extension of the previous work [1] in which the masses of these states were estimated with uncertainties too large to extract the reliable mass splitting. In the present study, by directly formulating a sum rule for the mass splitting, we obtain an improved prediction, $δM = M_{3/2^-} - M_{1/2^-} = -18.0^{+ 33.6}_{-17.1}$ MeV. This result provides a more quantitative insight into the spectrum of $P$-wave $Ω$ baryons and serves as a useful reference for future experiments.

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arXiv2025

Several conjectures from the hadron physics: The transient worlds beside(s) ours

The past decades witnessed the golden era of hadron physics, which gives us a good opportunity to study the physics happening in a transient period of time. The development on the singly heavy baryons indicates that there exists the fine structure of hadron spectrum caused by the direct strong interaction, and the development on the exotic hadrons indicates that the residue strong interaction is capable of forming the hadronic molecules. Similar to the electromagnetic interaction, the strong interaction may be capable of forming some imaginable hadronic worlds. Moreover, there can be various worlds formed by various fundamental physical laws. Some hadrons have so transient lifetimes that they may not even be formed. We discuss whether these non-existent particles are capable of affecting our realistic world. We discuss what kinds of particles exist, and so can be observed, in our realistic world. We conjecture that the ratios $R \equiv M/Γ\gg 1/2$ ($M τ\gg \hbar/2$) and $R \equiv M/Γ< 1/2$ ($M τ< \hbar/2$) can be used to describe the particles existing and not-existing in our realistic world, respectively. Here $M$, $Γ$, and $τ$ are the mass, width, and lifetime, respectively. We propose to use the ratio $R \equiv M/Γ\sim 1/2$ ($M τ\sim \hbar/2$) to describe the particles quasi-existing in our realistic world, whose studies may allow us to go beyond the quantum physics and arrive at another type of boundary of our realistic world, that is from the existent to the non-existent. We propose to investigate the quasi-existent particles by studying the singly heavy baryons through various imperfect symmetries among them. We obtain an incidental conjecture that the lifetime and width may be quantized for the particles existing in our realistic world as \begin{equation*}Mτ=n\hbar/2~~~{\rm{and}}~~~M/Γ=n/2\,,~~~n=1,2,3\cdots\,.\end{equation*}

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arXiv2025

$T_{bc\bar s}$ states in the process $Υ\to D^{-} \bar B^{0} D_s^{+}$

We perform a theoretical study of the decay process $Υ\to D^{-} \bar{B}^{0} D_s^{+}$ in search of the doubly heavy tetraquark states $T_{bc\bar{s}}$ with quark content $bc\bar{s}\bar{d}$. These $T_{bc\bar{s}}$ states are assumed to be dynamically generated molecular states from the S-wave interactions between $\bar{B}_s^{(*)0} D^{(*)+}$ and $\bar{B}^{(*)0} D_s^{(*)+}$ meson pairs. Based on the total angular momentum and the type of the constituent mesons (pseudoscalars $P$ or vectors $V$), they are labeled as $T_{bc\bar{s}}^{0, PP}$, $T_{bc\bar{s}}^{0, VV}$, and $T_{bc\bar{s}}^{2, VV}$, respectively. The $\bar{B}^{0} D_s^{+}$ invariant mass distribution for this decay is calculated using current algebra, incorporating contributions from $T_{bc\bar{s}}$ states arising from final-state interactions. Our results reveal a clear peak structure in the $7415 - 7425$ MeV region, which is attributed to the $T_{bc\bar{s}}^{2, VV}$ state. Additionally, a distinct dip structure appears near the $\bar{B}^{*0} D_s^{*+}$ threshold, characteristic of the $T_{bc\bar{s}}^{2, VV}$ as a hadronic molecular state. A near-threshold enhancement associated with the $T_{bc\bar{s}}^{0, PP}$ state and a dip arising from the $T_{bc\bar{s}}^{0,\,VV}$ state are also identified, though the manifestation of these features depends sensitively on model parameter fine-tuning. Therefore, with increased experimental statistics, the decay channel $Υ\to D^{-} \bar{B}^{0} D_s^{+}$ offers a promising avenue for discovering and characterizing the $T_{bc\bar{s}}$ states.

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arXiv2025

Topped baryons from QCD sum rules

The recent CMS observation of a near-threshold enhancement in top quark pair production provides the first experimental indication of a short-lived pseudoscalar $t\bar{t}$ bound state, commonly referred to as toponium. While most existing studies focus on toponium using perturbative QCD near threshold, baryonic configurations containing a single top quark -- singly topped baryons -- offer a complementary nonperturbative perspective. Notably, singly topped baryons are expected to exhibit a longer lifetime and a narrower decay width than toponium, since only one top quark decays rather than two. The heavy quark effective theory provides a natural and powerful framework for analyzing such systems, allowing the separation of heavy and light quark dynamics. In this work we employ heavy quark effective theory to investigate the internal structure of ground-state singly topped baryons. We construct their interpolating currents and analyze them using QCD sum rules. The resulting masses of the ground-state singly topped baryons are found to lie around 174 GeV, approximately $1.1$-$1.5$ GeV above the pole mass of the top quark.

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