Few-body systems

A new lower bound on 4-body ground-state energies has been derived in terms of two-body binding energies in the unequal mass case. For simple power-law potentials, this bound is compared to variational calculations and is shown to be very close to the exact result, particularly, for harmonic interactions. The stability of multiquark systems is revisited in a new quark model with chiral dynamics. Electromagnetic mass differences in potential models have been studied, pointing out some problems for charmed baryons. A quark-quark potential with a central part due to gluon exchange between extended quarks to instanton effects and a hyperfine term described as super-position of Gaussian functions has been determined. The form factors of π and K are analysed in the framework of the non-relativistic quark model, the stability of dibaryons consisting of 3 diquarks of different flavors has been studied. A study on diffractive scattering in QCD has been carried out. Within the resonating group method, the phase shifts of the hadron-hadron scattering are analyzed with applications to K - N interaction and meson-meson scattering. The Faddeev-Yakubovsky equations in configuration space have been solved with the aim of describing bound and scattering states of N = 4 interacting particles. Results concerning the scattering states of 4 nucleons in the isospin invariance approximation have been obtained for different (T, S) channels. They include: low energy parameters and elastic phase shifts for the N + 3N scattering below the 3N breakup threshold and S-matrix for the first N + 3N → 2N + 2N in elastic open channel (e.g. n+3He → d+d cross section). The method has also been applied to study the clusters of 2,3 and 4 4He atoms. (authors)