RPA finite-nucleus response to spin-isospin probes: investigation of the role of theoretical inputs on the strength distribution effects

Abstract

The author compares numerical results based on different interactions and assumptions for renormalised spin-isospin matrix elements within the RPA. Exact calculations are reported for the pion-like excitation JP=1+, T=1 in the finite (and small) nucleus 12C. The author presents a full comparison of the meson self-energy and response function matrix partial waves, and then compare the renormalised matrix elements of the longitudinal and transverse probes for a large range of momentum transfers (q=0-600 MeV/c). The author studies the following cases: (i) contact residual interaction with Delta -h configurations included; (ii) OPE+one rho exchange +g' term residual interaction in N-h space only and the question of the interrelation between Delta -h configurations and ad hoc renormalisations of the pi NN coupling constant; (iii) contact interaction in nucleon space only; and (iv) the question of pi NN form factors. These are compared with the more complete case where the pi and rho exchange and the g' term are taken into account together with non-nucleonic degrees of freedom. The author points out the implications of their results on nuclear structure calculations, where such effects are sometimes ignored, thereby examining some models of that field from the point of view of intermediate-energy theory. The role of the finite geometry turns out to be crucial in determining the shapes and features of the longitudinal and transverse responses. New insights into RPA results in electron scattering are gained, as well as limitations and requirements for future experimental tests of the theory.