Isospin breaking, coupled-channel effects, and X(3872)

We re-investigate the possibility of X(3872) as a $D\bar{D}^*$ molecule with $J^{PC}=1^{++}$ within the framework of both the one-pion-exchange (OPE) model and the one-boson-exchange (OBE) model. After careful treatment of the S-D wave mixing, the mass difference between the neutral and charged $D(D^*)$ mesons and the coupling of the $D(D^*)$ pair to $D^*\bar{D}^*$, a loosely bound molecular state X(3872) emerges quite naturally with large isospin violation in its flavor wave function. For example, the isovector component is 26.24% if the binding energy is 0.30 MeV, where the isospin breaking effect is amplified by the tiny binding energy. After taking into account the phase space difference and assuming the $3\pi$ and $2\pi$ come from a virtual omega and rho meson respectively, we obtain the ratio of these two hidden-charm decay modes: $\mathcal{B}(X(3872)\rightarrow \pi^+\pi^-\pi^0 J/\psi)/\mathcal{B}(X(3872)\rightarrow \pi^+\pi^- J/\psi)=0.42$ for the binding energy being 0.3 MeV, which is consistent with the experimental value.Comment: published in Phys. Rev.

The recoil correction and spin-orbit force for the possible B∗Bˉ∗B^* \bar{B}^{*} and D∗Dˉ∗D^* \bar{D}^{*} states

In the framework of the one-boson exchange model, we have calculated the effective potentials between two heavy mesons $B^* \bar{B}^{*}$ and $D^* \bar{D}^{*}$ from the t- and u-channel $\pi$-, $\eta$-, $\rho$-, $\omega$- and $\sigma$-meson exchanges. We keep the recoil corrections to the $B^* \bar{B}^{*}$ and $D^* \bar{D}^{*}$ systems up to $O(\frac{1}{M^2})$, which turns out to be important for the very loosely bound molecular states. Our numerical results show that the momentum-related corrections are favorable to the formation of the molecular states in the $I^G=1^+$, $J^{PC}=1^{+-}$ in the $B^* \bar{B}^{*}$ and $D^* \bar{D}^{*}$ systems.Comment: 12 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1403.404

Deuteron-like states composed of two doubly charmed baryons

We present a systematic investigation of the possible molecular states composed of a pair of doubly charmed baryons ($\Xi_{cc}\Xi_{cc}$) or one doubly charmed baryon and one doubly charmed antibaryon $(\Xi_{cc}\bar{\Xi}_{cc})$ within the framework of the one-boson-exchange-potential model. For the spin-triplet systems, we take into account the mixing between the ${}^3S_1$ and ${}^3D_1$ channels. For the baryon-baryon system $\Xi_{cc}\Xi_{cc}$ with $(R,I) = (\bar{3}, 1/2)$ and $(\bar{3}, 0)$, where $R$ and $I$ represent the group representation and the isospin of the system, respectively, there exist loosely bound molecular states. For the baryon-antibaryon system $\Xi_{cc}\bar{\Xi}_{cc}$ with $(R,I) = (8, 1)$, $(8, 1/2)$ and $(8,0)$, there also exist deuteron-like molecules. The $B_{cc}\bar{B}_{cc}$ molecular states may be produced at LHC. The proximity of their masses to the threshold of two doubly charmed baryons provides a clean clue to identify them.Comment: 18 pages, 8 figure

Possible hadronic molecules composed of the doubly charmed baryon and nucleon

We perform a systematical investigation of the possible deuteron-like bound states with configuration $\Xi_{cc}N (\bar{N})$, where $N(\bar{N})$ denotes the nucleon (anti-nucleon), in the framework of the one-boson-exchange-potential model. In the spin-triplet sector we take into account both the ${}^3S_1$ and ${}^3D_1$ channels due to non-vanishing tensor force. There exist several candidates of the loosely bound molecular states for the $\Xi_{cc}N$ and $\Xi_{cc}\bar{N}$ systems, which lie below the threshold of $\Lambda_c\Lambda_c$ or $\Lambda_c{\bar\Lambda}_c$. We also investigate the possible loosely bound states with configurations $\Lambda_cN(\bar{N})$ and $\Sigma_cN(\bar{N})$. These molecular candidates may be searched for at Belle II and LHC in the near future.Comment: 14 pages, 5 figure

Chiral Perturbation Theory and the BˉBˉ\bar B \bar B Strong Interaction

We have calculated the potentials of the heavy (charmed or bottomed) pseudoscalar mesons up to $O(\epsilon^2)$ with the heavy meson chiral perturbation theory. We take into account the contributions from the football, triangle, box, and crossed diagrams with the 2$\phi$ exchange and one-loop corrections to the contact terms. We notice that the total 2$\phi$-exchange potential alone is attractive in the small momentum region in the channel ${\bar B \bar B}^{I=1}$, ${\bar B_s \bar B_s}^{I=0}$, or ${\bar B \bar B_s}^{I=1/2}$, while repulsive in the channel ${\bar B \bar B}^{I=0}$. Hopefully the analytical chiral structures of the potentials may be useful in the extrapolation of the heavy meson interaction from lattice QCD simulation.Comment: 14 pages, 8 figures, 4 tables; discussion extended, references added, version published in Phys. Rev.