Relativistic, kinematically complete phenomenological expressions for the dilepton decay rates of nucleon resonances with arbitrary spin and parity are derived in terms of the magnetic, electric, and Coulomb transition form factors. The dilepton decay rates of the nucleon resonances with masses below 2 GeV are estimated using the extended vector meson dominance (VMD) model for the transition form factors. The model provides a unified description of the photo-and electroproduction data, γ (γ * )N → N * , the vector meson decays, N * → N ϕ (ω), and the dilepton decays, N * → N + − . The constraints on the transition form factors from the quark counting rules are taken into account. The parameters of the model are fixed by fitting the available photo-and electroproduction data and using results of the multichannel partial-wave analysis of the π N scattering. Where experimental data are not available, predictions of the non-relativistic quark models are used as an input. The vector meson coupling constants of the magnetic, electric, and Coulomb types are determined. The dilepton widths and the dilepton spectra from decays of nucleon resonances with masses below 2 GeV are calculated. C 2002 Elsevier Science (USA)

Finite temperature Euclidean SU (2) lattice gauge fields generated in the confinement phase close to the deconfinement phase transition are subjected to cooling. The aim is to identify long-living, almost-classical local excitations which carry (generically non-integer) topological charge. Two kinds of spatial boundary conditions (fixed holonomy and standard periodic boundary conditions) are applied. For the lowest-action almost-classical configurations we find that their relative probability semi-quantitatively agrees for both types of boundary conditions. We find calorons with unit topological charge as well as (anti-)selfdual lumps (BPS-monopoles or dyons) combined in pairs of non-integer (equal or opposite sign) topological charge. For calorons and separated pairs of equal-sign dyons obtained by cooling we have found that (i) the gluon field is well-described by Kraan-van Baal solutions of the Euclidean Yang-Mills field equations and (ii) the lowest Wilsonfermion modes are well-described by analytic solutions of the corresponding Dirac equation. For metastable configurations found at higher action, the multi-center structure can be interpreted in terms of dyons and antidyons, using the gluonic and fermionic indicators as in the dyon-pair case. Additionally, the Abelian monopole structure and field strength correlators between the centers are useful to analyse the configurations in terms of dyonic constituents. We argue that a semi-classical approximation of the non-zero temperature path integral should be built on superpositions of solutions with non-trivial holonomy.

We present a unified description of the vector meson and dilepton production in elementary and in heavy ion reactions. The production of vector mesons (ρ, ω) is described via the excitation of nuclear resonances (R).The theoretical framework is an extended vector meson dominance model

The effects of the presence of ∆-isobars in nuclear matter are studied in the framework of relativistic mean-field theory. The existence of stable nuclei at saturation density imposes constraints on the ∆-isobar self-energy and thereby on the meanfield coupling constants of the scalar and vector mesons with ∆-isobars. The range of possible values for the scalar and vector coupling constants of ∆-isobars with respect to the nucleon coupling is investigated and compared to recent predictions of QCD sum-rule calculations.