Spin structure of the Delta(1232) and inelastic Compton scattering

Radiative transitions gamma + Delta(1232) -> N^* are discussed in the nonrelativistic quark model with spin-orbit corrections for the 70-plet L^P=1^- nucleon resonances N^*. The reaction gamma + N -> gamma + Delta is considered as a tool to measure some of these transitions. A particular sensitivity to photoexcitations of S_{11}(1535), D_{13}(1700), and D_{15}(1675) is predicted.Comment: 4 pages, 1 figure. Talk given at NSTAR01, Mainz, German

The GDH sum rule for the Delta isobar: A possible anomaly?

The GDH sum rule is discussed for the Delta(1232) resonance. It is shown that apart from ordinary excitations to higher-energy states, the sum rule contains a large negative contribution due to de-excitation into the nucleon state. Therefore, a fulfillment of the sum rule assumes a strong coupling of Delta^+ and Delta^0 to resonances of spin 5/2 and higher. Calculations performed in quark models suggest that D15(1675) may be such a resonance. However, its strength is found to be not sufficient for bringing the GDH sum rule to a theoretically expected positive magnitude.Comment: 5 pages, no figures. Extended talk at the GDH2000 Symposium, Mainz, June 14-17, 2000. To appear in proceeding

Deuteron Compton scattering and electromagnetic polarizabilities of the nucleon

Differential cross section of deuteron Compton scattering has been calculated using the Bonn NN-potential, a consistent set of meson-exchange currents and seagulls, and lowest- and higher-order electromagnetic polarizabilities of the nucleon. Estimates of the polarizabilities of the neutron are obtained from recent experimental data.Comment: 3 pages, 2 figures, Latex2e with ps fonts. Talk at the FB16 Conference, Taipei, March 6-10, 2000. To appear in proceeding

Observation of eta-mesic nuclei in photoreactions: results and perspectives

Recent results from the LPI experiment on searching for eta-mesic nuclei in photoreactions are discussed and further perspectives are summarized.Comment: 4 pages, 4 figures. Talk given by G.A.S. at NSTAR01, Mainz, German

Dynamics of the vortex line density in superfluid counterflow turbulence

Describing superfluid turbulence at intermediate scales between the inter-vortex distance and the macroscale requires an acceptable equation of motion for the density of quantized vortex lines $\cal{L}$. The closure of such an equation for superfluid inhomogeneous flows requires additional inputs besides $\cal{L}$ and the normal and superfluid velocity fields. In this paper we offer a minimal closure using one additional anisotropy parameter $I_{l0}$. Using the example of counterflow superfluid turbulence we derive two coupled closure equations for the vortex line density and the anisotropy parameter $I_{l0}$ with an input of the normal and superfluid velocity fields. The various closure assumptions and the predictions of the resulting theory are tested against numerical simulations.Comment: 7 pages, 5 figure