Effect of the Tensor Force on Charge-Exchange Spin-Dependent Multipole Excitations

The charge-exchange spin-dipole (SD) and spin-quadrupole (SQ) strength functions of ⁹⁰Zr are calculated with and without the tensor terms of the Skyrme interaction in self−consistent HF+RPA approach. It is found that, in SD and SQ transitions, the RPA correlations associated with the tensor terms shift dramatically the strengths of (Y_lσ)_λ=l-1 and (Y_lσ)_λ=l modes upward and downward, respectively, and also shift the strengths of (Y_lσ)_λ=l+1 modes upward. The coupling between (Y_l=λ−1σ)_λ and (Y_l=λ+1σ)_λ modes arising from the tensor correlation is noticeable. The RPA tensor correlations produce strengths of SD and SQ modes, which are distributed in a much wider energy range, and the (Y_lσ)_λ=l−1 modes dominate the high energy part of the strength functions. These energy shifts and coupling effects of different modes can be understood qualitatively by expressing a finite range tensor force in a separable form.