Search

In this study, we explore the interactions between mesons and baryons in the open heavy sectors to identify potential triple-heavy molecular pentaquarks. We derive the meson-baryon interaction potentials using the vector meson exchange mechanism within the extended local hidden gauge formalism. The scattering amplitudes are computed by solving the coupled-channel Bethe-Salpeter equation, revealing several bound systems. By analyzing the poles of these amplitudes in the complex plane, we determine the masses and widths of these bound states. Additionally, we evaluate the couplings and compositeness of different channels within each bound system to assess their molecular characteristics. Our predictions include four $\Omega_{ccc}$-like states, four $\Omega_{bbb}$-like states, fourteen $\Omega_{bcc}$-like states, and ten $\Omega_{bbc}$-like states, which could be targets for future experimental investigations., Comment: 15 pages, 3 figures, add more references

In this work, we make a study of $T_{cc}^+$ state observed by the LHCb collaboration in 2021. In obtaining the effective potentials using the One-Boson-Exchange Potential Model we use an exponential form factor, and find that in the short and medium range, the contributions of the $\pi$, $\rho$ and $\omega$ exchanges are comparable while in the long range the pion-exchange contribution is dominant. Based on the assumption that $T_{cc}^+$ is a loosely bound state of $D^*D$, we focus on its three-body decay using the meson-exchange method. Considering that the difference between the thresholds of $D^{*+}D^0$ and $D^{*0}D^+$ is even larger than the binding energy of $T_{cc}^+$, the isospin-breaking effect is amplified by the small binding energy of $T_{cc}^+$. Explicitly including such an isospin-breaking effect we obtain, by solving the Schr\"{o}dinger equation, that the probability of the isoscalar component is about $91\%$ while that of the isovector component is around $9\%$ for $T_{cc}^+$. Using the experimental value of the mass of $T_{cc}^+$ as an input, we obtain the wave function of $T_{cc}^+$ and further obtain its width via the three-body hadronic as well as the radiative decays. The total width we obtain is in agreement with the experimental value of the LHCb measurement with a unitarised Breit-Wigner profile. Conversely, the current results support the conclusion that $T_{cc}^+$ is a hadronic molecule of $D^*D$., Comment: 10 pages, 2 figures

In this study, we reconsider the states $Z_b(10610)$ and $Z_b(10650)$ by investigating the presence of diquark-anti-diquark components as well as the hadronic molecule components in the framework of effective field theory. The different masses of pseudoscalar mesons such as $\pi^{0}$, $\eta_{8}$, and $\eta_{0}$, as well as vector mesons like $\rho^{0}$ and $\omega$ violate the OZI rule that is well depicted under the $[U(3)_L\otimes U(3)_R]_{global}\otimes [U(3)_V]_{local}$ symmetry. To account for the contribution of intermediate bosons of heavy masses within the OBE model, we introduce an exponential form factor instead of the commonly used monopole form factor in the past. By solving the coupled-channel Schr\"{o}dinger equation with the Gaussian expansion method, our numerical results indicate that the $Z_b(10610)$ and $Z_b(10650)$ states can be explained as hadronic molecules slightly mixing with diquark-anti-diquark states., Comment: 9 pages, 2 figures

In this work, we investigate the double-heavy molecular pentaquark states with the quark contents $ccss\bar{s}$, $bbss\bar{s}$, and $bcss\bar{s}$ by using the coupled channel approach. The extended local hidden gauge Lagrangians are used to obtain the meson-baryon interactions by exchanging the vector mesons. We predict some candidates for the molecular states with the quantum numbers $I(J^{P}) = 0(1/2^{-}, 3/2^{-}, 5/2^{-})$, whose binding energies are of the order of $20-30$ MeV and whose widths are all less than $8$ MeV. These predicted exotic double-heavy molecular pentaquark states may be accessible in future experiments such as LHCb., Comment: Minor corrections are made

We recall that the chiral unitary approach for the interaction of pseudoscalar mesons with the baryons of the decuplet predicts two states for the $\Xi(1820)$ resonance, one with a narrow width and the other one with a large width. We contrast this fact with the recent BESIII measurement of the $K^- \Lambda$ mass distribution in the $\psi(3686)$ decay to $K^- \Lambda \bar\Xi^+ $, which demands a width much larger than the average of the PDG, and show how the consideration of the two $\Xi(1820)$ states provides a natural explanation to this apparent contradiction., Comment: 9 pages, 3 figures

With the chiral unitary approach, we evaluate the hidden strange $B_{c}$-like molecular states of $b\bar{c}s\bar{s}$ systems $\bar{B}_{s}\bar{D}_{s}$, $\bar{B}_{s}^{*}\bar{D}_{s}$, $\bar{B}_{s}\bar{D}_{s}^{*}$, and $\bar{B}_{s}^{*}\bar{D}_{s}^{*}$ coupled to the non-strange channels. The $S$-wave scattering amplitudes are calculated based on the vector meson exchange, four pseudoscalar mesons contact interactions, and four vector mesons contact interactions obtained from the extended local hidden gauge approach. We find six states below the threshold of the most relevant channel. The binding energies of these states are around $1-10$ MeV and the widths are around $0.2-0.7$ MeV. Our research is a supplement to the mass spectra of $B_{c}$-like states, which may be useful for the experimental search in the future., Comment: 15 pages, 8 figures

The decay process $\Xi_{b}^{-} \rightarrow pK^{-}K^{-}$ is studied with the final state interaction approach by considering the contributions from the $S$-wave meson-baryon interactions, and also the intermediate state $\Lambda(1520)$ in the $D$-wave. The low-lying resonances $\Lambda(1405)$ and $\Lambda(1670)$ have significant contributions, which are both dynamically generated from the $S$-wave final state interactions with isospin $I=0$. Furthermore, the $\Lambda(1520)$ state also has important contributions from $D$-wave. With these resonances contributions, the experimental data of the lower $pK^{-}$ invariant mass distributions are well described. We also discuss the contribution of another resonance in the $S$-wave with isospoin $I=1$, which cannot be ignored. Moreover, some of the branching fractions obtained for the corresponding decay channels are consistent with the experimental measurements., Comment: 18 pages, 6 figures, 3 tables, published in Phys. Rev. D

In this work, we construct the Lagrangian describing meson-diquark interaction, such that the diquark-anti-diquark component as well as the molecular component is introduced when studying the $Z_{cs}$ states. In this way, the problem is solved that if only considering the $\bar{D}^{(*)}D_s^{(*)}$ components, the potentials are suppressed by OZI rule. Through solving the Bethe-Salpeter equation, we find that the $Z_{cs}(4000)^+$ can be explained as the mixture of $\bar{D}^{*0}D_s^+$ and $\bar{A}_{cs}S_{cu}$ components. Besides, for the $\bar{D}^{*0}D_s^{*+}/\bar{A}_{cs}A_{cu}$ system, the pole of $4208\pm 13i$ MeV on the second Riemann sheet is predicted, whose mass agrees with that of $Z_{cs}(4220)^+$ while the width is much smaller than $Z_{cs}(4220)^+$. Due to the large error of the $Z_{cs}(4220)^+$'s width, further measurements are expected. In addition, several other poles of different spins are predicted., Comment: 6 pages, 1 figure

We investigate the $D_{s}^{+} \rightarrow K^{+} K^{-} \pi^{+}$ decay theoretically with the final state interactions, which is based on the chiral unitary approach and takes into account the external and internal $W$-emission mechanisms at the quark level. Only considering three resonances contributions, the $f_0(980)$ in $S$-wave, the $\bar {K}^{*}(892)^{0}$ and $\phi(1020)$ in $P$-wave, one can make a good description of the recent experimental data from BESIII Collaboration, where the contribution from $S$-wave is found to be small. Besides, we also make a calculation of the corresponding branching fractions, which are consistent with the results of BESIII Collaboration and Particle Data Group., Comment: More discussions were made. Welcome for comments

We perform a systematic exploration of the possible doubly charmed molecular pentaquarks composed of $\Sigma_c^{(*)}D^{(*)}$ with the one-boson-exchange potential model. After taking into account the $S-D$ wave mixing and the coupled channel effects, we predict several possible doubly charmed molecular pentaquarks, which include the $\Sigma_cD$ with $I(J^P) = 1/2(1/2^-)$, $\Sigma_c^*D$ with $1/2(3/2^-)$, and $\Sigma_cD^*$ with $1/2(1/2^-)$, $1/2(3/2^-)$. The $\Sigma_cD$ state with $3/2(1/2^-)$ and $\Sigma_cD^*$ state with $3/2(1/2^-)$ may also be suggested as candidates of doubly charmed molecular pentaquarks. The $\Sigma_cD$ and $\Sigma_c^*D$ states can be searched for by analyzing the $\Lambda_cD\pi$ invariant mass spectrum of the bottom baryon and $B$ meson decays. The $\Sigma_cD^*$ states can be searched for in the invariant mass spectrum of $\Lambda_cD^*\pi$, $\Lambda_cD\pi\pi$ and $\Lambda_cD\pi\gamma$. Since the width of $\Sigma_c^*$ is much larger than that of $D^*$, $\Sigma_c^*D\rightarrow \Lambda_cD\pi$ will be the dominant decay mode. We sincerely hope these candidates for the doubly charmed molecular pentaqurks will be searched by LHCb or BelleII collaboration in the near future., Comment: 10 pages,1 figure

In 2012, we investigated the possible molecular states composed of two charmed mesons [Phys.Rev. D 88, 114008 (2013), arXiv:1211.5007 [hep-ph](2012)]. The $D^*D$ system with the quantum numbers of $I(J^P)=0(1^+)$ was found to be a good candidate of the loosely bound molecular state. This state is very close to the $D^*D$ threshold with a binding energy around 0.47 MeV. This prediction was confirmed by the new LHCb observation of $T_{cc}^+$ [see Franz Muheim's talk at the European Physical Society conference on high energy physics 2021]., Comment: 2 pages, 2 figures

We study the magnetic moments and transition magnetic moments of $P_c$ and $P_{cs}$ states in the molecular picture. We first revisit the magnetic moments of $P_c$ states as the $S$ wave molecular states without coupled channel effects. The coupled channel effects and the $D$ wave contributions are then investigated carefully. The coupled channel effects contribute to the change of $0.1\sim 0.4$ nuclear magneton $\mu_N$ for most cases while the $D$ wave only induces the variation of less than $0.03 ~\mu_N$. In addition, we obtain the transition magnetic moments between different $P_c$ states and the related electromagnetic decay widths of $P_c'\to P_c\gamma$. The magnetic moments of $P_{cs}$ are much different for the assumption of spin being 1/2 and 3/2. The study of electromagnetic properties will help us disclose further the structure of these unconventional states., Comment: 8 pages, 5 tables; version appeared in Phys. Rev. D

Inspired by the newly observed $Z_{cs}^-(3985)$ by BESIII collaboration, we study the structure of this particle in the picture of $D_s^{(*)-}D^{(*)0}$ molecular state. Firstly we systematically construct the Lagrangians which describing the interaction of charmed mesons, taking into account the chiral and hidden local symmetries. With the obtained effective potentials from the Lagrangians constructed, we solve the coupled channel Bethe-Salpeter equation with the on-shell approximation. On the third Reimann sheet, a pole position of around $3982.34-i0.53$ MeV is obtained, which can be associated to the $Z_{cs}^-(3985)$ and explained as a loose bound state of $D_s^*\bar{D}^*$., Comment: 6 pages, 1 figure

In the present work, we investigate the decays of $B^{0}_{s} \rightarrow \phi\pi^{+}\pi^{-}$ and $B^{0} \rightarrow \phi\pi^{+}\pi^{-}$ with the final state interactions based on the chiral unitary approach. In the final state interactions of the $\pi^+\pi^-$ with its coupled channels, we study the effects of the $\eta\eta$ channel in the two-body interactions for the reproduction of the $f_{0}(980)$ state. Our results for the $\pi^+\pi^-$ invariant mass distributions of the decay $B^{0}_{s} \rightarrow \phi\pi^{+}\pi^{-}$ describe the experimental data up to 1 GeV well, with the resonance contributions from the $f_{0}(980)$ and $\rho$. For the predicted invariant mass distributions of the $B^{0} \rightarrow \phi\pi^{+}\pi^{-}$ decay, we found that the contributions from the $f_{0}(500)$ are significant except for the ones from the $f_{0}(980)$ state. With some experimental branching ratios as input to determine the production vertex factors, we make some predictions for the branching ratios of the other final decay channels, including the vector mesons, in the $B^0_{(s)}$ decays, where some of them are consistent with the experimental ones within the uncertainties., Comment: More comments are added

Using the vector-exchange interaction in the local hidden gauge approach, which in the light quark sector generates the chiral Lagrangian, and has produced realistic results for $\Omega_c, \Xi_c, \Xi_b$ and the hidden charm pentaquark states, we study the meson-baryon interactions in the coupled channels that lead to the $\Xi_{bb}$ and $\Omega_{bbb}$ excited states of the molecular type. We obtain seven states of the $\Xi_{bb}$ type with energies between $10408$ and $10869$ MeV and one $\Omega_{bbb}$ state at $15212$ MeV., Comment: v1:17 pages, 19 tables; v2: 20 pages, 19 tables, discussion added, references added, version to appear in Chin. Phys. C

The newly observed $\Xi(1620)^0$ by the Belle Collaboration inspires our interest in performing a systematic study on the interaction of an anti-strange meson $(\bar{K}^{(*)})$ with a strange or doubly strange ground octet baryon $\mathcal{B}$ ($\Lambda$, $\Sigma$, and $\Xi$), where the spin-orbit force and the recoil correction are considered in the adopted one-boson-exchange model. Our results indicate that $\Xi(1620)^0$ can be explained as a $\bar{K}\Lambda$ molecular state with $I(J^P)=1/2(1/2^-)$ and the intermediate force from $\sigma$ exchange plays an important role. Additionally, we also predict several other possible molecular candidates, i.e., the $\bar{K}\Sigma$ molecular state with $I(J^P)=1/2(1/2^-)$ and the triply strange $\bar{K}\Xi$ molecular state with $I(J^P)=0(1/2^-)$., Comment: 7 pages, 5 figures, and 4 tables

On March 26th, 2019, at the Rencontres de Moriond QCD conference, the LHCb Collaboration reported the observation of three new pentaquarks, namely $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$, which are consistent with the loosely bound molecular hidden-charm pentaquark states composed of an S-wave charmed baryon $\Sigma_c$ and an S-wave anti-charmed meson ($\bar{D}, \bar{D}^*$). In this work, we present a direct calculation by the one-boson-exchange (OBE) model and demonstrate explicitly that the $P_c(4312)$, $P_c(4440)$ and $P_c(4457)$ do correspond to the loosely bound $\Sigma_c\bar{D}$ with $(I=1/2,J^P=1/2^-)$, $\Sigma_c\bar{D}^*$ with $(I=1/2,J^P=1/2^-)$ and $\Sigma_c\bar{D}^*$ with $(I=1/2,J^P=3/2^-)$, respectively., Comment: 5 pages, 1 table and 2 figures. Accepted by Phys. Rev. D as Rapid Communication

We study the three-body systems of $\bar{K}^{(*)}B^{(*)}\bar{B}^{(*)}$ by solving the Faddeev equations in the fixed-center approximation, where the light particle $\bar{K}^{(*)}$ interacts with the heavy bound states of $B\bar{B}$ ($B^*\bar{B}^*$) forming the clusters. In terms of the very attractive $\bar{K}^*B$ and $\bar{K}^*B^*$ subsystems, which are constrained by the observed $B_{s1}(5830)$ and $B_{s2}^*(5840)$ states in experiment, we find two deep bound states, containing the hidden-bottom components, with masses $11002\pm 63$ MeV and $11078\pm 57$ MeV in the $\bar{K}^*B\bar{B}$ and $\bar{K}^*B^*\bar{B}^*$ systems, respectively. The two corresponding states with higher masses of the above systems are also predicted. In addition, using the constrained two-body amplitudes of $\bar{K}B^{(*)}$ and $\bar{K}\bar{B}^{(*)}$ via the hidden gauge symmetry in the heavy-quark sector, we also find two three-body $\bar{K}B\bar{B}$ and $\bar{K}B^{*}\bar{B}^*$ bound states., Comment: Version to be published in Phys. Rev. D

We study the electromagnetic form factors of the doubly charmed baryons, using covariant chiral perturbation theory within the extended on-mass-shell (EOMS) scheme. Vector-meson contributions are also taken into account. We present results for the baryon magnetic moments, charge and magnetic radii. While some of the chiral Lagrangian parameters could be set to values determined in previous works, the available lattice results for $\Xi_{cc}^+$ and $\Omega_{cc}^+$ only allow for robust constraints on the low-energy constant (LEC) combination, $c_{89}(=-\frac{1}{3}c_8+4c_9)$. The couplings of the doubly charmed baryons to the vector mesons have been estimated assuming the Okubo--Zweig--Iizuka (OZI) rule. We also give the expressions for the form factors of the double beauty baryons considering the masses predicted in the framework of quark models. A comparison of our results with those obtained in heavy baryon chiral perturbation theory (HBChPT) at the same chiral order is made., Comment: 24 pages, 8 figures

In this work, we study higher bottomonia up to the $nL=8S$, $6P$, $5D$, $4F$, $3G$ multiplets using the modified Godfrey-Isgur (GI) model, which takes account of color screening effects. The calculated mass spectra of bottomonium states are in reasonable agreement with the present experimental data. Based on spectroscopy, partial widths of all allowed radiative transitions, annihilation decays, hadronic transitions, and open-bottom strong decays of each state are also evaluated by applying our numerical wave functions. Comparing our results with the former results, we point out difference among various models and derive new conclusions obtained in this paper. Notably, we find a significant difference between our model and the GI model when we study $D, F$, and $G$ and $n\ge 4$ states. Our theoretical results are valuable to search for more bottomonia in experiments, such as LHCb, and forthcoming Belle II., Comment: 40 pages, 4 figures and 40 tables. Accepted by Eur. Phys. J. C

Using the local hidden gauge approach, we study the possibility of the existence of bottomed strange molecular states with isospin 0. We find three bound states with spin-parity $0^+$, $1^+$ and $2^+$ generated by the $\bar{K}^*B^*$ and $\omega B_s^*$ interaction, among which the state with spin 2 can be identified as $B_{s2}^*(5840)$. In addition, we also study the $\bar{K}^*B$ and $\omega B_s$ interaction and find a bound state which can be associated to $B_{s1}(5830)$. Besides, the $\bar{K}B^*$ and $\eta B_s^*$ and $\bar{K}B$ and $\eta B_s$ systems are studied, and two bound states are predicted. We expect that further experiments can confirm our predictions., Comment: 11 pages, 28 figures

Stimulated by the BESIII observation of $X(2100)$, $X(2500)$, and $\eta(2225)$, we try to pin down new pseudoscalar meson nonets including these states. The analysis of mass spectra and the study of strong decays indicate that $X(2120)$ and $\eta(2225)$ associated with $\pi(2070)$ and the predicted kaon $K(2150)$ may form a new pseudoscalar meson nonet. In addition, more experimental data for $X(2100)$ are necessary to determine its structure of nonets. Then, $X(2500)$, $X(2370)$, $\pi(2360)$, and the predicted kaon $K(2414)$ can be grouped into another new nonet. These assignments to the discussed pseudoscalar states can be further tested in experiment., Comment: 15 pages, 4 tables and 10 figures. More discussions added and typos corrected. Accepted by Phys. Rev. D

The D0 Collaboration has recently seen a resonant-like peak in the $B_s\pi$ invariant mass spectrum, claimed to be a new state called $X(5568)$. Using a $B_s\pi$--$B\bar{K}$ coupled channel analysis, implementing unitarity, and with the interaction derived from Heavy Meson Chiral Perturbation Theory, we are able to reproduce the reported spectrum, with a pole that can be associated to the claimed $X(5568)$ state, and with mass and width in agreement with the ones reported in the experimental analysis. However, if the $T$-matrix regularization is performed by means of a momentum cutoff, the value for the latter needed to reproduce the spectrum is $\Lambda = 2.80 \pm 0.04\ \text{GeV}$, much larger than a "natural" value $\Lambda \simeq 1\ \text{GeV}$. In view of this, it is difficult to interpret the nature of this new state. This state would not qualify as a resonance dynamically generated by the unitarity loops. Assuming the observed peak to correspond to a physical state, we make predictions for partners in the $D$, $D^\ast$, and $B^\ast$ sectors. Their observation (or lack thereof) would shed light into this issue.

We first construct the effective chiral Lagrangians for the $1^{-+}$ exotic mesons. With the infrared regularization scheme, we derive the one-loop infrared singular chiral corrections to the $\pi_1(1600)$ mass explicitly. We investigate the variation of the different chiral corrections with the pion mass under two schemes. Hopefully, the explicit non-analytical chiral structures will be helpful to the chiral extrapolation of the lattice data from the dynamical lattice QCD simulation of either the exotic light hybrid meson or tetraquark state., Comment: 15 pages, 5 figures, references added, revised. Version to be published in Chinese Physics C

In this work, we investigate the mass corrections of the doubly charmed baryons up to $N^2LO$ in the extended-on-mass-shell (EOMS) renormalization scheme, comparing with the results of heavy baryon chiral perturbation theory. We find that the terms from the heavy baryon approach are a subset of those obtained in the EOMS scheme. By fitting the lattice data, we can determine the parameters $\tilde{m}$, $\alpha$, $c_1$ and $c_7$ from the Lagrangian, while in the heavy baryon approach no information on $c_1$ can be obtained from the baryons mass. Correspondingly, the masses of $m_{\Xi_{cc}}$ and $m_{\Omega_{cc}}$ are predicted, in the EOMS scheme, extrapolating the results from different values of the charm quark and the pion masses of the lattice QCD calculations., Comment: 7 pages, 11 figures

In this review we give a perspective of the theoretical work done recently on the interpretation of results from $B$, $D$, $\Lambda_b$, $\Lambda_c$ weak decays into final states that contain interacting hadrons, and how it is possible to obtain additional valuable information that is increasing our understanding of hadron interactions and the nature of many hadronic resonances. The novelty of these processes is that one begins with a clean picture at the quark level which allows one to select the basic mechanisms by means of which the process proceeds. Finally, one has a final state described in terms of quarks. To make contact with the experiments, where mesons and baryons are observed, one must hadronize, creating pairs of $q \bar q$ and writing the new states in terms of mesons and baryons. This concludes the primary hadron production in these processes. After that, the interaction of these hadrons takes place, offering a rich spectrum of resonances and special features from where it is possible to learn much about the interaction of these hadrons and the nature of many resonances in terms of the components of their wave functions., Comment: Review paper comissioned for International Journal of Modern Physics E

In this work we study the $\rho B^*\bar{B}^*$ three-body system solving the Faddeev equations in the fixed center approximation. We assume the $B^*\bar{B}^*$ system forming a cluster, and in terms of the two-body $\rho B^*$ unitarized scattering amplitudes in the local Hidden Gauge approach we find a new $I(J^{PC})=1(3^{--})$ state. The mass of the new state corresponds to a two particle invariant mass of the $\rho B^\ast$ system close to the resonant energy of the $B^\ast_2(5747)$, indicating that the role of this $J=2$ resonance is important in the dynamical generation of the new state.

In this paper we study the relationship between the $D_{s0}^{*}(2317)^+$ resonance and the decay of the $B_c$ meson into $J/\psi DK$. In this process, the $B_c$ meson decays first into $J/\psi$ and the quark pair $c\bar{s}$, and then the quark pair hadronizes into $DK$ or $D_s\eta$ components, which undergo final state interaction. This final state interaction, generating the $D_{s0}^{*}(2317)^+$ resonance, is described by the chiral unitary approach. With the parameters which allow us to match the pole position of the $D_{s0}^{*}(2317)^+$, we obtain the $DK$ invariant mass distribution of the decay $B_c\to J/\psi DK$, and also the rate for $B_c\to J/\psi D_{s0}^{*}(2317)$. The ratio of these two magnitude is then predicted., Comment: 10 figures

In this work, we study systems composed of a $\rho/\omega$ and $B^*$ meson pair. We find three bound states in isospin, spin-parity channels $(1/2, 0^+)$, $(1/2, 1^+)$ and $(1/2, 2^+)$. The state with $J=2$ can be a good candidate for the $B_2^*(5747)$. We also study the $\rho B$ system, and a bound state with mass $5728$ MeV and width around $20$ MeV is obtained, which can be identified with the $B_1(5721)$ resonance. In the case of $I=3/2$, one obtains repulsion and thus, no exotic (molecular) mesons in this sector are generated in the approach.

The chiral dynamics of the doubly heavy baryons is solely governed by the light quark. In this work, We have derived the chiral corrections to the mass of the doubly heavy baryons up to N$^3$LO. The mass splitting of $\Xi_{cc}$ and $\Omega_{cc}$ at the N$^2$LO depends on one unknown low energy constant $c_7$. With the experimental mass of $\Xi_{cc}(3520)$ as the input, we estimate the mass of $\Omega_{cc}$ to be around 3.678 GeV. Moreover, we have also performed a systematical analysis of the chiral corrections to the axial currents and axial charges of the doubly heavy baryons. The chiral structure and analytical expressions will be very useful to the chiral extrapolations of the future lattice QCD simulations of the doubly heavy baryons., Comment: 10 pages, 2 tables, 3 figure. Accepted by Phys. Rev. D

In this work, we study the interaction between a nucleon and a $P$-wave charmed meson in the $T$ doublet by exchanging a pion. Our calculations indicate that a nucleon and a $P$-wave charmed meson with $J^P=0^+$ or $J^P=1^+$ in the $T$ doublet can form bound states. We propose the experimental search for these exotic molecular states near the $D_1(2420)N$ and $D_2^*(2460)N$ thresholds, where Belle, LHCb and the forthcoming Belle II have the discovery potential for them., Comment: 10 pages, 4 tables, 3 figure. Accepted by Phys. Rev. D

In this work, we have adopted the spin rearrangement scheme in the heavy quark limit and extensively investigated three classes of the radiative decays: $\mathfrak{M}\to (b\bar{b})+\gamma$, $(b\bar{b})\to \mathfrak{M}+\gamma$, $ \mathfrak{M} \to \mathfrak{M}^\prime+\gamma$, corresponding to the electromagnetic transitions between one molecular state and bottomonium, one bottomonium and molecular state, and two molecular states respectively. We also extend the same formalism to study the radiative decays of the molecular states with hidden charm. We have derived some model independent ratios when the initial or final states belong to the same spin flavor multiplet. Future experimental measurement of these ratios will test the molecular picture and explore the underlying structures of the $XYZ$ states., Comment: 21 pages, 10 tables Accepted by Phys.Rev.D

In the past decade, many new charmonium (or charmonium-like) and bottomonium (or bottomonium-like) states were observed experimentally. I will review these XYZ states which do not fit into the quark model spectrum easily., Comment: Plenary talk at the XV International Conference on Hadron Spectroscopy-Hadron 2013, 4-8 November 2013, Nara, Japan

We have studied the loosely bound $D^*\bar{D}^*$ system. Our results indicate that the recently observed charged charmonium-like structure $Z_c(4025)$ can be an ideal $D^*\bar{D}^*$ molecular state. We have also investigated its pionic, dipionic, and radiative decays. We stress that both the scalar isovector molecular partner $Z_{c0}$ and three isoscalar partners ${\tilde Z}_{c0,c1,c2}$ should also exist if $Z_c(4025)$ is a $D^*\bar{D}^*$ molecular state {in the framework of the one-pion-exchange model}. $Z_{c0}$ can be searched for in the channel $e^+e^-\to Y \to Z_{c0}(4025)\left(\pi\pi\right)_{P-wave}$ where $Y$ can be Y(4260) or any other excited $1^{--}$ charmonium or charmonium-like states such as Y(4360), Y(4660) etc. The isoscalar $D^*\bar{D}^*$ molecular states ${\tilde Z}_{c0,c2}$ with $0^+(0^{++})$ and $0^+(2^{++})$ can be searched for in the three pion decay channel $e^+e^-\to Y \to {\tilde Z}_{c0,c2} \left(3\pi\right)^{I=0}_{P-wave}$. The isoscalar molecular state ${\tilde Z}_{c1}$ with $0^-(1^{+-})$ can be searched for in the channel ${\tilde Z}_{c1}\eta$. Experimental discovery of these partner states will firmly establish the molecular picture., Comment: 6 pages, 1 figure and 2 tables. Typos corrected

We perform a coupled-channel study of the possible deuteron-like molecules with two heavy flavor quarks, including the systems of $D^{(*)}D^{(*)}$ with double charm, $\bar{B}^{(*)}\bar{B}^{(*)}$ with double bottom and $D^{(*)}\bar{B}^{(*)}$ with both charm and bottom, within the one-boson-exchange model. In our study, we take into account the S-D mixing which plays an important role in the formation of the loosely bound deuteron, and particularly, the coupled-channel effect in the flavor space. According to our calculation, the states $D^{(*)}D^{(*)}[I(J^P)=0(1^+)]$ and $(D^{(*)}D^{(*)})_s[J^P=1^+]$ with double charm, the states $\bar{B}^{(*)}\bar{B}^{(*)}[I(J^P)=0(1^+),0(2^+),1(0^+),1(1^+),1(2^+)]$, $(\bar{B}^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+,2^+]$ and $(\bar{B}^{(*)}\bar{B}^{(*)})_{ss}[J^P=0^+,1^+,2^+]$ with double bottom, and the states $D^{(*)}\bar{B}^{(*)}[I(J^P)=0(0^+),0(1^+)]$ and $(D^{(*)}\bar{B}^{(*)})_s[J^P=0^+,1^+]$ with both charm and bottom are good molecule candidates. However, the existence of the states $D^{(*)}D^{(*)}[I(J^P)=0(2^+)]$ with double charm and $D^{(*)}\bar{B}^{(*)}[I(J^P)=1(1^+)]$ with both charm and bottom is ruled out., Comment: 1 figure added, published in Physical Review D

Within the past ten years many new hadrons states were observed experimentally, some of which do not fit into the conventional quark model. I will talk about the few-body systems composed of heavy quarks, including the charmonium-like states and some loosely bound states., Comment: Plenary talk at the 20th International IUPAP Conference on Few-Body Problems in Physics, to appear in Few Body Systems (2013)

With the one-boson-exchange model, we study the interaction between the S-wave $D^{(*)}/D^{(*)}_s$ meson and S-wave $B^{(*)}/B^{(*)}_s$ meson considering the S-D mixing effect. Our calculation indicates that there may exist the $B_c$-like molecular states. We estimate their masses and list the possible decay modes of these $B_c$-like molecular states, which may be useful to the future experimental search., Comment: 7 pages, 2 figures, 5 tables. Typos corrected. Version published in Phys. Rev. D

Inspired by the observed Y(2175) state, we predict its non-strange partner Y(1915), which has a resonance structure with mass around 1915 MeV and width about $317\sim 354$ MeV. Experimental search for Y(1915) is proposed by analyzing the $\omega f_0(980)$ or $\omega \pi\pi$ invariant mass spectrum of the $e^+e^-\to \omega f_0(980), \omega \pi\pi$ and $J/\psi\to \eta \omega f_0(980)$ processes, which are accessible at Belle, BaBar, BESIII and forthcoming BelleII. Considering similarity between two families, the comparison of the mass spectra of $\omega$ and $\phi$ families can provide important information on the 1D state of $\phi$ family, $\phi(1910)$, which has a very broad resonance structure with mass around 1910 MeV regarded as the strangeonium partner of $\omega(1650)$. This also answers the question why the 1D state $\phi(1910)$ is still missing in experiment. This is supported by our former study on the properties of Y(2175), which explains Y(2175) as the 2D strangeonium because our theoretical total width is comparable with the Belle data., Comment: 5 pages, 5 figures. More discussions and numerical results added. Typos corrected

In the framework of the one-boson-exchange model, we have studied the interaction of the $B^*\bar{B}$ and $B^*\bar{B}^{*}$ system. After considering the S-wave and D-wave mixing, we notice that both $Z_b(10610)^\pm$ and $Z_b(10650)^\pm$ can be interpreted as the $B^*\bar{B}$ and $B^*\bar{B}^{*}$ molecular states quite naturally. Within the same framework, there also exist several molecular charmonia including X(3872) and several other molecular bottomonia, which are the partners of $Z_b(10610)$ and $Z_b(10650)$. The long-range one-pion-exchange force alone is strong enough to form these loosely bound molecular states, which ensures the numerical results quite model-independent and robust., Comment: 11 pages, 6 tables

With the one-boson-exchange model we have studied the possible existence of the very loosely bound hidden-charm molecular baryons composed of anti-charmed meson and charmed baryon. Our numerical results indicate that there exist $\Sigma_c\bar{D}^*$ states with $I(J^P)=1/2(1/2^-), 1/2(3/2^-), 3/2(1/2^-), 3/2(3/2^-)$ and $\Sigma_c\bar{D}$ state with $3/2(1/2^-)$. But the $\Lambda_c \bar{D}$ and $\Lambda_c \bar{D}^*$ molecular states do not exist., Comment: 8 pages, 2 tables, 3 figures. Matches version accepted for publication in Chinese Physics C