We investigate the low-energy interactions between the charmonium state J/ψ and the light pseudoscalar mesons (π and K) within the framework of dispersion relations. We demonstrate that the symmetry-breaking terms in the chiral Lagrangian induce mixing between the bare charmonium fields, necessitating a diagonalization procedure to correctly identify the physical J/ψ and ψ′ states. Using the resulting diagonalized Lagrangian, we construct the crossed-channel amplitudes for J/ψJ/ψ→PP¯ and incorporate the ππ and KK¯ rescattering effects through dispersion relations. This framework is used consistently both in the phenomenological extraction of the transition parameters from ψ′ → J/ψππ and in the continuation of the crossed amplitudes to the near-threshold J/ψP(P=π,K) region. As a result, we determine both the scattering lengths and the effective ranges. We obtain the upper-bound estimates aJ/ψπ≲−0.0037 fm and aJ/ψK≲−0.049 fm, where the negative sign indicates an attractive interaction without a bound state in our convention. Our results show that the J/ψK interaction is moderately enhanced relative to the pion channel, driven by explicit chiral symmetry breaking. Furthermore, a quantitative comparison of the coupled-channel mechanism, where J/ψπ and J/ψK couple to open-charm channels, reveals that both J/ψπ and J/ψK scatterings are predominantly governed by the soft-gluon exchange mechanism.

A model-independent parameterization of the low-energy scattering amplitude that incorporates the left-hand cut from one-particle exchange, an extension of the conventional effective-range expansion (ERE), was recently proposed and successfully applied to the low-energy DD^* system [Phys. Rev. Lett. 135, 011903 (2025)]. While the original formulation is based on a nonrelativistic approximation and is thus limited to a [1,1] approximant for self-consistency, we extend the framework by explicitly including the higher-order terms up to 𝒪(k^6). We systematically investigate the reliability and robustness of the generalized ERE by incorporating relativistic kinematic effects. In addition, we develop a relativistic version of the ERE that accounts for lhc contributions. These results affirm the generalized ERE as a robust and systematically improvable framework for near-threshold scattering processes, providing both analytical and numerical reliability for applications in two-body scattering problems with a particle exchange.

We apply the generalized effective-range expansion of Phys. Rev. Lett. 135, 011903(2025), which incorporates the left-hand cut from one-pion exchange, to low-energy neutron-proton scattering in the ^1S_0 and ^3S_1 channels. The amplitude zero for the center-of-mass momentum near 0.35 GeV in the ^1S_0 channel is naturally accommodated within this framework. We extract the pole position, scattering length, effective range, and the pseudoscalar pion-nucleon coupling constant g_πN^2/(4π) at different expansion orders. The low-energy parameters are stable and consistent with established values, while g_πN^2/(4π) exhibits larger uncertainties. The extraction of g_πN^2/(4π) is data-driven, relying on the analytic constraints from the left-hand cut and phase-shift data within the one-pion-exchange approximation. Despite larger uncertainties compared to high-precision extractions, the consistency with established values demonstrates that this framework can probe the left-hand-cut singularity.

We present a unified analysis of the Z_c(3900) and Z_cs(3985) states considering both experimental and lattice data. The study simultaneously includes the processes e^+e^- → J/ψπ^+π^-, J/ψK^+ K^-, D^0 D^∗- π^+, (D^∗ 0 D_s^-+D^0 D_s^∗ -) K^+, together with finite-volume energy levels from recent lattice QCD simulations. Open-charm meson loops with triangle singularities, the J/ψπ(J/ψK̅)-D̅D^*(D̅D^*_s) coupled-channel interactions, and the ππ-KK̅ final-state interaction are all taken into account. We find that pole contributions associated with the Z_c(3900) and Z_cs(3985) are indispensable for describing the data. The successful joint description of the experimental and lattice data supports the interpretation that the Z_c(3900) and Z_cs(3985) are SU(3) flavor partners within the same octet multiplet and indicates that both are resonance states. The extracted pole masses and half-widths of the Z_c(3900) and the Z_cs(3985) are (3879.6 ± 4.8) MeV and (32.2 ± 4.7) MeV, and (3976.9 ± 5.1) MeV and (28.8 ± 5.9) MeV, respectively. The ratios of the Z_c(Z_cs) couplings to the DD̅^*(D_sD̅^∗+DD̅_s^∗) and J/ψπ(J/ψK) channels are also determined. A compositeness analysis indicates that, although the DD̅^* (D_sD̅^∗+DD̅_s^∗) component in the Z_c(3900) (Z_cs(3985)) state is sizable, additional components are still needed to form these exotic states.

We reanalyze the lattice spectra for I=1/2 Dπ scattering in the A_1^+ irreducible representation from [Phys. Rev. D 111, 014503 (2025)] to investigate the impact of chiral and SU(3) flavor symmetries in S-wave Dπ scattering and the D_0^*(2300) resonance. By fitting the phase shifts obtained via Lüscher's formula with both traditional and chirally modified effective-range expansion and K-matrix parameterizations, we find that the chiral factor shifts the extracted pole mass closer to the threshold (especially for resonances) and substantially reduces the resonance width. These findings are confirmed by unitarized chiral perturbation theory through a direct fit to the lattice spectra with both the single-channel and the Dπ-Dη-D_sK̅ coupled-channel schemes. Once the coupled channels are incorporated, the two-pole structure of the D_0^*(2300) emerges. The trajectories of the two poles are investigated by varying the pion mass.

We reanalyze, considering the contribution of P-wave charmonia, lattice data for the DD-DSDS coupled-channel of Prelovsek et al. [J. High Energy Phys. 06 (2021) 035.] and DD* systems of Prelovsek et al. [Phys. Rev. Lett. 111, 192001 (2013).] with m pi <^> 280 and 266 MeV, and L = 24a/32a (a <^> 0.09 fm) and L = 16a (a <^> 0.1239(13) fm), respectively. The hidden-charm states with JPC = 0++, 1++, and 2++ quantum numbers are then searched for. For 0++, the analysis reveals three poles in the DD-DSDS coupled-channel amplitude, corresponding to three states. Two of these poles, located near the DD and DSDS thresholds, can be interpreted as mostly molecular states. A third pole above the DSDS threshold is originated from the P-wave chi c0(2P) charmonium state. The number of poles found in the DD-DSDS system is the same as that found in the original lattice analysis though the position of the third pole changes sizeably. In the 1++ sector, we find two poles in the complex energy plane. The first one is related to the molecular X(3872) state, with a compositeness exceeding 90%, while the second one, stemming from the chi c1(2P) charmonium, appears above the DD* threshold and it likely corresponds to the recently discovered chi c1(4010) state. In the 2++ sector, we also report two poles and find that the dressed chi c2(2P) is lighter than the D*D* molecular state, with the dynamics of the latter closely related to that of the heavy-quark spin-symmetry partner of the X(3872). Our exploratory study of the 1++ and 2++ sectors offers valuable insights into their dynamics, but given that the fits that we carry out are underconstrained, more lattice data are required to draw robust conclusions.

The low-energy J/ψ N scattering is of significant importance for various reasons. It is deeply interconnected with the hidden-charm P_c pentaquark states, provides insights into the role of gluons in nucleon structures, and is pertinent to the properties of J/ψ in nuclear medium. The scattering can occur through two distinct mechanisms: the coupled-channel mechanism involving open-charm meson-baryon intermediate states Λ_c D̅^(*) and Σ_c^(*)D̅^(*), and the soft-gluon exchange mechanism. In this study, we investigate the S-wave J/ψ N scattering length arising from both mechanisms. Our findings indicate that both mechanisms lead to attractive interactions, yielding scattering lengths of [-10, -0.1] × 10^-3 fm for the coupled-channel mechanism and <-0.16 fm for the soft-gluon exchange mechanism, respectively. Notably, the soft-gluon exchange mechanism produces a scattering length that is at least one order of magnitude larger than that from the coupled-channel mechanism, indicating its predominance. These findings can be corroborated through lattice calculations and will enhance our understanding of scattering processes that violate the Okubo-Zweig-Iizuka rule.

The validity range of the widely used traditional effective range expansion can be severely limited by the presence of a left-hand cut near the two-particle threshold. Such a left-hand cut emerges in two-particle scattering processes involving either a light particle exchange in the t-channel or a particle exchange with a mass slightly heavier than the mass difference of the two particles in the u-channel, which occurs in a wide range of physical systems. We propose a new parameterization for the low-energy scattering amplitude that incorporates these left-hand cuts arising from particle exchange diagrams. This parameterization extends the convergence radius of the effective range expansion beyond the branch point of the left-hand cut and is applicable to a broad range of systems. The parameterization enables the extraction of coupling strengths between the exchange particle and the scattering particles, and reveals amplitude zeros resulting from the interplay between short- and long-range interactions. We demonstrate the effectiveness of this new parameterization through its application to DD^* scattering with meson masses obtained in a lattice QCD calculation.

The validity range of the time-honored effective range expansion can be very limited due to the presence of a left-hand cut close to the two-particle threshold. Such a left-hand cut arises in the two-particle interaction involving a light particle exchange with a small mass or a mass slightly heavier than the mass difference of the two particles, identified as a long-range force, a scenario encountered in a broad range of systems. This can hinder a precise extraction of low-energy scattering observables and resonance poles. To address this issue, we propose a new parametrization for the low-energy scattering amplitude that accounts for the left-hand cut. The parametrization is like a Pade approximation but with nonanalytic terms from the left-hand cut and can be regarded as an extension of the effective range expansion. This parametrization is versatile and applicable to a broad range of systems with Yukawa-type interactions, including particle, hadronic, nuclear, cold atom, and quantum gas systems. In particular, it should be invaluable in understanding various near-threshold hadron resonances. As byproducts, we also show that the parametrization can be used to extract the couplings of the exchanged particle to the scattering particles, and derive expressions for amplitude zeros caused by the interplay between the short- and long-range interactions.

By solving the Lippmann-Schwinger equation, possible hadronic molecules in the $D^*\bar K$-$D\bar K^*$ coupled-channel system are investigated with the one-meson exchange potentials, where both vector and pseudoscalar mesons are considered as exchange particles. We find an S-wave virtual state with mass $M=2487$ MeV, and a resonance with $M=2759$ and width $\Gamma=18$ MeV. In the $D^* \bar K$ invariant mass distribution, the virtual state appears as a cusp at the $D^*\bar K$ threshold, while the resonance potentially manifests as a dip. In particular, we take into account the $D\bar K \pi$ three-body dynamics due to the on-shell pion exchange and the finite decay width for $\bar K^*$.

Motivated by the updated analysis of the G(3900) by the BESIII Collaboration, we perform a global analysis of the cross sections of the e+e--* DD, e+e--* DD* + c.c., e+e--* D*D* processes, especially focusing on the properties of the G(3900). As the energy region of interest is limited by the next opening threshold, i.e., the D1D threshold, we focus on the energy region [3.7, 4.25] GeV, where three charmonia r(1D), r(3S), and r(2D) explicitly contribute to the cross sections. By constructing the P-wave contact interaction between the (D; D*) doublet and its antiparticle in the heavy quark limit, we extract the physical scattering amplitude by solving the Lippmann-Schwinger equation. No matter whether three or two charmonium states are included in our framework, we always find a dynamically generated state corresponding to the G(3900), which suggests it to be a P-wave dynamically generated state. We also predict several dynamically generated states in the corresponding 1-+ channel. These states can be further searched for in the electron-positron annihilation process involving the emission of a single photon.

By solving the Lippmann-Schwinger equation, possible hadronic molecules in the D⁎K¯-DK¯⁎ coupled-channel system are investigated with the one-meson exchange potentials, where both vector and pseudoscalar mesons are considered as exchange particles. We find an S-wave virtual state with mass M=2487 MeV, and a resonance with M=2759 and width Γ=18 MeV. In the D⁎K¯ invariant mass distribution, the virtual state appears as a cusp at the D⁎K¯ threshold, while the resonance potentially manifests as a dip. In particular, we take into account the DK¯π three-body dynamics due to the on-shell pion exchange and the finite decay width for K¯⁎.

The low-energy J/ψ N scattering is important for various reasons: it is related to the hidden-charm P_c pentaquark states, provides insights into the role of gluons in nucleon structures, and is relevant to the J/ψ properties in nuclear medium. The scattering can happen through two distinct mechanisms: the coupled-channel mechanism via open-charm meson-baryon intermediate states, and the soft-gluon exchange mechanism. We investigate the J/ψ N S-wave scattering length through both mechanisms, and find that the soft-gluon exchange mechanism leads to a scattering length at least one order of magnitude larger than that from the coupled-channel mechanism and thus is the predominant one. The findings can be verified by lattice calculations and will enhance our understanding of the scattering processes breaking the Okubo-Zweig-Iizuka rule.

We present a detailed study of the lowest-lying 1/2(-) and 3/2(-) Lambda Q resonances both in the heavy 2 2 quark (bottom and charm) and the strange sectors. We have paid special attention to the interplay between the constituent quark-model and chiral baryon-meson degrees of freedom, which are coupled using a unitarized scheme consistent with leading-order heavy quark symmetries. We show that the Lambda(b)(5912) [J(P) = 1/2(-)], Lambda(b)(5920) [J(P) = 3/2(-)] and the Lambda(c)(2625) [J(P) = 3/2-], and the Lambda(1520) [J(P) = 3/2(-)] admitting larger breaking corrections, are heavyquark spin-flavor siblings. They can be seen as dressed quark-model states with Sigma Q(()*()) pi molecular components of the order of 30%. The J(P)=1(-) Lambda(2595) has, however, a higher molecular 2 probability of at least 50%, and even values greater than 70% can be easily accommodated. This is because it is located almost on top of the threshold of the Sigma(c)pi pair, which largely influences its properties. Although the light degrees of freedom in this resonance would be coupled to spin-parity 1(-) as in the Lambda(b)(5912), Lambda(b)(5920) and Lambda(c)(2625), the Lambda(c)(2595) should not be considered as a heavy-quark spin-flavor partner of the former ones. We also show that the Lambda(1405) chiral two-pole pattern does not have analogs in the 1 - charmed and bottomed sectors, because the 2 N D-(*()) and N (B) over bar (()*()) channels do not play for heavy quarks the decisive role that the N (K) over bar does in the strange sector, and the notable influence of the bare quark-model states for the charm and bottom resonances. Finally, we predict the existence of two Lambda(b)(6070) and two Lambda(c)(2765) heavy-quark spin and flavor sibling odd parity states.

A coupled-channel approach is applied to the charged tetraquark state $T_{cc}^+$ with special attention paid to the three-body dynamics. The three-body unitarity is preserved as both the pion exchange between the $D$ and $D^*$ mesons and the finite $D^*$ width are taken into account simultaneously. The low-energy scattering parameters, namely the scattering length and effective range are extracted with a low-energy expansion of the $D^*D$ scattering amplitude. The compositeness parameter is calculated and is found to be close to unity, which implies a molecular nature of the $T_{cc}^+$. By making use of the heavy-quark spin symmetry, an isoscalar $D^*D^*$ molecular partner of the $T_{cc}^+$ with $J^P=1^+$ is predicted under the assumption that the $D^*D$-$D^*D^*$ coupled-channel effects can be neglected.

We present a detailed study of the lowest-lying 12− and 32− ΛQ resonances both in the heavy quark (bottom and charm) and the strange sectors. We have paid special attention to the interplay between the constituent quark-model and chiral baryon-meson degrees of freedom, which are coupled using a unitarized scheme consistent with leading-order heavy quark symmetries. We show that the Λb(5912) [JP=1/2−], Λb(5920) [JP=3/2−] and the Λc(2625) [JP=3/2−], and the Λ(1520) [JP=3/2−] admitting larger breaking corrections, are heavy-quark spin-flavor siblings. They can be seen as dressed quark-model states with ΣQ(∗)π molecular components of the order of 30%. The JP=12− Λc(2595) has, however, a higher molecular probability of at least 50%, and even values greater than 70% can be easily accommodated. This is because it is located almost on top of the threshold of the Σcπ pair, which largely influences its properties. Although the light degrees of freedom in this resonance would be coupled to spin-parity 1− as in the Λb(5912), Λb(5920) and Λc(2625), the Λc(2595) should not be considered as a heavy-quark spin-flavor partner of the former ones. We also show that the Λ(1405) chiral two-pole pattern does not have analogs in the 12− charmed and bottomed sectors, because the ND(∗) and NB¯(∗) channels do not play for heavy quarks the decisive role that the NK¯ does in the strange sector, and the notable influence of the bare quark-model states for the charm and bottom resonances. Finally, we predict the existence of two Λb(6070) and two Λc(2765) heavy-quark spin and flavor sibling odd parity states.

By solving the Lippmann-Schwinger equation, possible hadronic molecules in the D^*K̅-DK̅^* coupled-channel system are investigated with the one-meson exchange potentials, where both vector and pseudoscalar mesons are considered as exchange particles. We find an S-wave virtual state with mass 2472(18) MeV, and a resonance with mass M=2747(31) and width Γ=7(3) MeV. In the D^* K̅ invariant mass distribution, the virtual state appears as a cusp at the D^*K̅ threshold, while the resonance potentially manifests as a dip. In particular, we take into account the DK̅π three-body dynamics due to the on-shell pion exchange and the finite decay widths for D^* and K̅^*. Additionally, the cutoff dependence and the SU(4) breaking effect are investigated in our work. Our results also indicate that the accurate measurement for the decay width of the DK̅^* resonance can help us to evaluate the SU(4) breaking effect in the future.

We present a detailed study of the lowest-lying 12− and 32− ΛQ resonances both in the heavy quark (bottom and charm) and the strange sectors. We have paid special attention to the interplay between the constituent quark-model and chiral baryon-meson degrees of freedom, which are coupled using a unitarized scheme consistent with leading-order heavy quark symmetries. We show that the Λb(5912) [JP=1/2−], Λb(5920) [JP=3/2−] and the Λc(2625) [JP=3/2−], and the Λ(1520) [JP=3/2−] admitting larger breaking corrections, are heavy-quark spin-flavor siblings. They can be seen as dressed quark-model states with ΣQ(∗)π molecular components of the order of 30%. The JP=12− Λc(2595) has, however, a higher molecular probability of at least 50%, and even values greater than 70% can be easily accommodated. This is because it is located almost on top of the threshold of the Σcπ pair, which largely influences its properties. Although the light degrees of freedom in this resonance would be coupled to spin-parity 1− as in the Λb(5912), Λb(5920) and Λc(2625), the Λc(2595) should not be considered as a heavy-quark spin-flavor partner of the former ones. We also show that the Λ(1405) chiral two-pole pattern does not have analogs in the 12− charmed and bottomed sectors, because the ND(∗) and NB¯(∗) channels do not play for heavy quarks the decisive role that the NK¯ does in the strange sector, and the notable influence of the bare quark-model states for the charm and bottom resonances. Finally, we predict the existence of two Λb(6070) and two Λc(2765) heavy-quark spin and flavor sibling odd parity states.

We perform a unified description of the experimental data of the π+π− and J/ψπ± invariant mass spectra for e+e− → J/ψπ+π− and the D0D*− mass spectrum for e+e− → D0D*−π+ at e+e− center-of-mass energies 4.23 and 4.26 GeV. The analysis takes into account open-charm meson loops that contain triangle singularities, the J/ψπ-DD̅^* coupled-channel interaction respecting unitarity, and the strong ππ-KK̅ final state interaction using dispersion relations. The analysis leads to a precise determination of the Zc(3900) pole with the pole mass and width (3880.7 ± 1.7stat ± 22.4syst) MeV and (35.9 ± 1.4stat ± 15.3syst) MeV, respectively, and hints at that the DD̅^* molecular and non-molecular components are of similar importance in the Zc(3900) formation.

Hidden-charm exotic hadrons will be searched for and investigated at future electron-ion colliders. For instance, the X(3872) can be produced through the exclusive process γp→X(3872)p. The vector meson dominance model has been commonly employed in estimating the cross sections of such processes. However, the coupled-channel production mechanism through open-charm meson-baryon intermediate states may play a crucial role. To assess the significance of such contributions, we estimate the cross section of the γp→X(3872)p reaction assuming the coupled-channel mechanism. For energies near the threshold, the total cross section is predicted to be of tens of nanobarns for γp→X(3872)p, which can be measured at future experimental facilities. Furthermore, the open-charm coupled-channel mechanism leads to a distinct line shape of the total cross section that can be utilized to reveal the production dynamics.