Charge-exchange dipole excitations in neutron-rich nuclei: −1ħω₀, anti-analog pygmy and anti-analog giant resonances

The occurrence of low-lying charge-exchange non-spin-flip dipole modes below the giant resonance in neutron-rich nuclei is predicted on the basis of nuclear density functional theory. The ground and excited states are described within the framework of the self-consistent Hartree–Fock–Bogoliubov theory and the proton-neutron quasiparticle-random-phase approximation employing a Skyrme-type energy density functional. The model calculations are performed for the spherical neutron-rich Ca, Ni, and Sn isotopes. It is found that the low-lying states appear sensitive to the shell structure associated with the −1ħω₀ excitation below the Gamow–Teller states. Furthermore, the pygmy resonance emerges below the giant resonance when the neutrons occupy the low -ℓ (ℓ ≤ 2-3 ) orbitals analogous to the pygmy resonance seen in the electric-dipole response