The possibility of imposing partially twisted boundary conditions is investigated for the scalar sector of lattice QCD. According to the commonly shared belief, the presence of quark-antiquark annihilation diagrams in the intermediate state generally
hinders the use of the partial twisting. Using effective field theory techniques in a finite volume, and studying the scalar sector of QCD with total isospin I=1, we however demonstrate that partial twisting can still be performed, despite the fact that annihilation diagrams are present. The reason for this are delicate cancellations, which emerge due to the graded symmetry in partially quenched QCD with valence, sea and ghost quarks. The modified Luescher equation in case of partial twisting is given.
We discuss the possibilities of producing the X(3872), which is assumed to be a D bar D^* bound state, in radiative decays of charmonia. We argue that the ideal energy regions to observe the X(3872) associated with a photon in e^+e^- annihilations ar
e around the Y(4260) mass and around 4.45 GeV, due to the presence of the S-wave D bar D_1(2420) and D^* bar D_1(2420) threshold, respectively. Especially, if the Y(4260) is dominantly a D bar D_1 molecule and the X(3872) a D bar D^* molecule, the radiative transition strength will be quite large.
In this paper we propose a model-independent method to extract the resonance parameters on the lattice directly from the Euclidean 2-point correlation functions of the field operators at finite times. The method is tested in case of the two-point fun
ction of the Delta-resonance, calculated at one loop in Small Scale Expansion. Further, the method is applied to a 1+1-dimensional model with two coupled Ising spins and the results are compared with earlier ones obtained by using Lueschers approach.
We examine the possibility to extract information about the DN and DbarN interactions from the pbar d to D Dbar N reaction. We utilize the notion that the open-charm mesons are first produced in the annihilation of the antiproton on one nucleon in th
e deuteron and subsequently rescatter on the other (the spectator) nucleon. The latter process is then exploited for investigating the DN and DbarN interactions. We study different methods for isolating the contributions from the D^0p and D^-p rescattering terms.
We present a gauge invariant approach to photoproduction of mesons on nucleons within a chiral unitary framework. The interaction kernel for meson-baryon scattering is derived from the chiral effective Lagrangian and iterated in a Bethe-Salpeter equa
tion. Within the leading order approximation to the interaction kernel, data on kaon photoproduction from SAPHIR, CLAS and CBELSA/TAPS are analyzed in the threshold region. The importance of gauge invariance and the precision of various approximations in the interaction kernel utilized in earlier works are discussed.
We investigate the Dbar-N interaction at low energies using a meson-exchange model supplemented with a short-distance contribution from one-gluon-exchange. The model is developed in close analogy to the meson-exchange KN interaction of the Juelich gr
oup utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (rho, omega) exchange and higher-order box diagrams involving D*N, DDelta, and D*Delta intermediate states. The short range part is assumed to receive additional contributions from genuine quark-gluon processes. The predicted cross sections for Dbar-N for excess energies up to 150 MeV are of the same order of magnitude as those for KN but with average values of around 20 mb, roughly a factor two larger than for the latter system. It is found that the omega-exchange plays a very important role. Its interference pattern with the rho-exchange, which is basically fixed by the assumed SU(4) symmetry, clearly determines the qualitative features of the Dbar-N interaction -- very similiar to what happens also for the KN system.
