Microscopic Dynamics of Large-Scale Deformation and Shape Coexistence in Nuclei

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1)To explore soft modes of excitation in unstable nuclei close to the neutron drip line, we have systematically carried out quasiparticle RPA calculations taking into account pairing correlations, deformations of the mean field, and excitations into the continuum. The result indicates that a new kind of soft mode associated with the neutron skin degree of freedom will emerge : in particular, in deformed neutron rich nuclei, low-frequency 0+ excitations will be generated by coherent motions of anisotropic pair fluctuations and deformations of the neutron skin.2)We have formulated a new theory of large amplitude collective motion, called Adiabatic Self-Consistent Collective Coordinate (ASCC) method, that is invariant against a gauge transformation associated with particle number fluctuations. This theory has been applied to the shape coexistence phenomena in nuclei around Se68. We have thus succeeded in microscopically determining the collective path that connects the oblate and prolate local minima in the mean field. We have found a significant enhancement of collective inertia due to the time-odd components of the mean field.