Spin-isospin strength and spectral functions

The issue of spin-isospin strength is addressed from the perspective of the information that is available about one-nucleon spectral functions. Both the effect of ground-state correlations and of the coherence by random-phase-approximation correlations are then incorporated in a natural way. The results for ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ are confronted with those obtained by earlier methods, which have been criticized recently. It is shown that ground-state correlations produce a large amount of strength in the first 20 MeV above the main peaks of the Gamow-Teller and spin-dipole resonances. They also yield for these nuclei with rather large neutron excess considerable (n,p) strength, therby increasing the total (p,n) strength by 25–30 %. In spite of this, the strength within the hitherto analyzed energy domains is not enhanced by these correlations. It is argued that a large amount of quasifree background that is assumed in the analysis of charge exchange reactions consists of broad distributions of genuine charge exchange strength.