Spin-triplet proton-neutron pair in spin-dipole excitations

Background: Spin-triplet proton-neutron pairing in nuclei has been under debate. It is well known that the dynamical pairing affects the nuclear matrix element of the Gamow-Teller (GT) transition and the double decay. Purpose: We investigate the effect of the -pair interaction in the channel on the low-lying spin-dipole (SD) transition. We then aim at clarifying the distinction of the role in between the SD and GT transitions. Method: We perform a three-body model calculation for the transition , where is taken as a core. The strength of the pair interaction is varied to see the effect on the SD transition-strength distribution. To fortify the finding obtained by the three-body model, we employ the nuclear energy-density functional method for the SD transitions in several nuclei, where one can expect a strong effect. Results: The effect of the -pair interaction depends on the spatial overlap of the pair and the angular momentum of the valence nucleons; the higher the angular momentum of the orbitals, the more significant the effect. Conclusions: The dynamical pairing is effective even for SD states, although the spatial overlap of the pair can be smaller than GT states. The SD transition involving high- orbitals with the same principal quantum number is strongly affected by the dynamical pairing.