N. Auerbach

Probing for Dirac vacuum structure in nuclei

Abstract Recent Dirac-equation analyses of nucleon-nucleus interactions indicate weak dependence of the effective potentials on nucleon energy, and suggest that associated with any large nucleus is an “island” of ≈ 10 3 discrete negative-energy nucleon bound states. Experimental searches for this structure would be a critical test of the Dirac-equation picture. Possible experiments as well as open theoretical issues are discussed.

A microscopic phenomenological approach to the spreading widths of giant resonances

Abstract Spreading widths of giant resonances are calculated in the framework of an extended response function HF-RPA theory in which nucleon self-energy corrections for the particle and hole are introduced. These are obtained from phenomenological nucleon-optical potentials. It is argued that in addition to the self-energies a consistent account of the coupling of 1p-1h states to more complicated configuration requires the introduction of a renormalized ph interaction containing an imaginaary term. This interaction is parameterized in terms of a zero-range density-dependent interaction. A prescription to determine the form of this induced imaginary interaction is suggested. The isoscalar monopole and quadrupole as well as the isovector monopole and dipole giant resonances are treated numerically.

Excitation of giant resonances in the Ca isotopes in (π±, π0) reactions

Abstract The excitation of the giant isovector dipole and monopole resonances in the even- A Ca isotopes in pion single-charge-exchange reactions is studied theoretically. Transition densities obtained from a sum-rule approach and from a microscopic charge-exchange RPA are employed in DWIA calculations. The relation of the ( π ± , π 0 ) cross sections to proton and neutron densities is discussed.