[en] Many properties of hadrons (both baryons and mesons) can be parametrized exactly in the spin-flavor space, using only a few general group and dynamical properties of QCD. This exact parametrization has two important features: a) Its structure turns out to have a form typical of a non relativistic quark model (NRQM) in spite of the fact that the method is fully relativistic (although non covariant); b) Terms of increasing complexity in the parametrization have decreasing coefficients; therefore usually only a few terms are important and suffice to reproduce the data fairly well. This 'hierarchy' of coefficients explains not only why the 'naive' NRQM works, but also why other models, such as chiral bags or very different ones, are all capable of reproducing fairly the data. It is enough, for this, that the model under consideration is sufficiently flexible to contain those few parameters that correspond to the dominant ones of the exact QCD parametrization. The above conclusions will be exemplified in particular on the baryon masses and magnetic moments. (author)

[en] Following Iraq withdrawal from Kuwait, the United Nations Security Council adopted its resolution 687 (1991), setting out the terms of the cease fire agreement. Those terms, inter alia, requested the Director General of the International Atomic Energy Agency (IAEA) to carry out immediate on-site inspection of Iraq nuclear capabilities, to prepare and carry out a plan for the destruction, removal and rendering harmless of all assets relevant to the design and production of nuclear weapons, and to design and eventually implement a plan for the ongoing monitoring and verification of Iraq compliance with its related obligations under Security Council resolutions. This paper summarises the work of the IAEA Iraq Action Team, established by the Director General to carry out the practical tasks necessary to implement the requests of the Security Council. It also highlights the lessons learned from a unique regime of disarmament and verification. (author)

[en] In the light of the << General Parametrization Method>> and the new mass relationships recently derived by Morpurgo, we discuss the old problem of assigning a definite mass to a broad resonance, the Δ(1232). A value of (1214.6 ± 3.5) MeV is obtained for the Δ⁺⁺ mass as the real part of the pole in the complex plane

[en] Recent photoabsorption experiments in the Δ resonance region in heavy nuclei are recently obtained, in addition to the older ones in light elements. This prompts a renewed theoretical investigation of the effects in the Δ photoexcitation in nuclei. The authors discuss in the present paper both the gross properties of the cross section, particularly its behavior as a function of the atomic number A, as well as more detailed dynamical features. As regards the first point the authors show that, under certain assumptions, the integrated cross section takes naturally the form of an energy weighted sum rule, whereas more sophisticated microscopical models must be used in order to explain the detailed shape of the cross section

[en] A simple non relativistic field theoretical model is proposed for a system of pions interacting with nucleons in the region of the Δ(1232) resonance. The model is suitable for the calculation of the hypothetical quasi-bound (nucleon-Δ) state with quantum numbers T=2, Jsup(P)=2⁺. The results of this calculation are given and compared with the previous ones already known in the literature

[en] We derive, using the general QCD parametrization, the approximate relation r²(π⁺) - r²(K⁺) ≅ -r²(K⁰) where the r's are the charge radii. The relation is satisfied but the experimental errors are still sizeable. The derivation is similar to (but even simpler than) that for r²(p) - r²(n) ≅ r²(Δ⁺) (orig.)

[en] The effects of the short range correlations combined with the Pauli principle on the δ in nuclear matter are analyzed in terms of a model in which a g-matrix interaction between the δ and the nucleons is explicitly introduced. The model is also suitable in the frame of the E E L L correction. (author)

[en] In the context of possible precursor phenomena of a phase transition in nuclear matter, the effects of the dressing of π and rho mesons on the relevant p-h spin-isospin-dependent residual interaction g' have been considered. Our model takes into account the contributions to g' due to the direct exchange of π and rho mesons in the presence of short-range correlations. Since the exact self-energies are expressed effectively through g', one is faced with a self-consistent problem which has been solved numerically at increasing densities. The results show a remarkable dependence of the residual interaction on the density as well as on the momentum, together with a rather different behaviour in the longitudinal (π) channel as compared to the transverse (rho) one. The general trend is an increase in g' which, depending on the model parameters such a rho coupling strength, cut-offs and background term, may prevent the onset of the precritical situation even at very high densities. When the precritical condition is attained, the mechanism of self-consistency shifts the critical momentum up to a value depending only on the range of the repulsive core and narrows considerably the momentum region for the amplification of the pion field

No abstract available

[en] The expansion is analyzed of the proper self-energy for an infinite system of interacting fermions in terms of the Fermi momentum ksub(F), when also the incident momentum is of the same order as ksub(F). Rules are given for determining the order in ksub(F) of a proper self-energy diagram. In particular, the occurrence of diagrams which contribute to the same order in ksub(F), but have a different number of hole lines has been discussed, as well as the appearance of diagrams with logarithmic singularities. (author)