Effects of the delta-isobar (Δ) mixing on the spin-isospin response functions in finite nuclei are studied in the quasielastic region. A method to calculate the response function for a finite system composed of nucleon (N) and Δ is formulated in a ring approximation. It is designed to treat the Δ-related Landau-Migdal parameters ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$, ${\mathrm{g}}_{\mathrm{\Delta }\mathrm{\Delta }}^{\prime }$ and the nucleon parameter ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$, independently, so that the universality ansatz, ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$=${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$=${\mathrm{g}}_{\mathrm{\Delta }\mathrm{\Delta }}^{\prime }$, is removed. We calculated the isovector spin-longitudinal and -transverse response functions, ${\mathrm{R}}_{\mathrm{L}}$ and ${\mathrm{R}}_{\mathrm{T}}$, with and without the Δ mixing. Inclusion of Δ enhances ${\mathrm{R}}_{\mathrm{L}}$ but reduces ${\mathrm{R}}_{\mathrm{T}}$ for ordinary interactions. Dependence of ${\mathrm{R}}_{\mathrm{L},\mathrm{T}}$ on ${\mathrm{g}}_{\mathrm{NN}}^{\prime }$ and ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$ is investigated. Decomposition into the process-decomposed response functions, ${\mathrm{R}}^{\left[\mathrm{NN}\right]}$, ${\mathrm{R}}^{\left[\mathrm{N}\mathrm{\Delta }\right]}$, and ${\mathrm{R}}^{\left[\mathrm{\Delta }\mathrm{\Delta }\right]}$, is very elucidative to see the Δ effects, which are found to be mainly governed by ${\mathrm{R}}^{\left[\mathrm{N}\mathrm{\Delta }\right]}$ and sensitive to ${\mathrm{g}}_{\mathrm{N}\mathrm{\Delta }}^{\prime }$. The isovector spin-transverse response function ${\mathrm{R}}_{\mathrm{T}}^{(\mathrm{e},\mathrm{e}\prime )}$ obtained by (e,e′) is calculated by various effective interactions and compared to each other as well as experimental data.

• Received 8 August 1994

DOI:https://doi.org/10.1103/PhysRevC.51.269