Vibrational properties of soft dipole states

Vibrational properties of soft dipole states in 11Li are discussed. The particle-vibration coupling model, in which the soft dipole states in 11Li can be formed by coupling a 1- vibrational state of 10He with the 0p3/2 proton, is shown to explain the energy shift and strength distribution of the soft dipole strength in 11Li. The model explains the appearance of the two peaks observed in the experimental low-energy dipole strength distribution in 11Li. Possible existence of double dipole states, and of the giant dipole resonance built on the soft dipole states and on double soft dipole states, is also discussed. The difference from the cases of 11Be and 19C is pointed out, as well as the importance of the measurements of magnetic moments and hfs anomalies in Be and C isotopes. (author)