Microscopic study of soft and giant dipole resonances in $^{6}$He

We present our recent work on the electric dipole response (E1) of $^{6}$He with a fully microscopic six-body calculation [Ref: Phys. Rev. C 89, 064303 (2014)]. The wave functions of the ground and excited states are expressed as a combination of explicitly correlated Gaussians. Final state interactions of three-body decay channels are explicitly taken into account. The ground state properties and the low-lying E1 strength are obtained consistently with observations. Two-peak structure appears in the strength function. The peak at the high-energy region indicates a typical macroscopic picture of the giant dipole resonance, the out-of-phase proton-neutron motion, whereas the lower-lying peaks exhibit in-phase proton-neutron motion in the internal region, out-of-phase motion near the surface region, and spatially extended neutron oscillation, indicating a soft-dipole mode and its vibrationally excited mode. The compressional dipole strength is also examined and discussed in relation to the soft-dipole mode.