Microscopic study of triaxial deformation and non-principal-axis rotation in rapidly rotating nuclei

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Recent experimental data suggest that an interesting phenomenon of the triaxial deformation, in which all three lengths of principal axes of the nuclear mean-field are different from each other, appears near the yrast states. In this resarch, with this triaxial deformation as a keyword, we shed new light on mechanism of the appearance of new non-principal-axis rotations, which is a consequence of triaxiality and leads to a tilting of rotation-axis with respect to the deformation axes.In these two year's of research, we have accomplished several important achievements, but still there are some parts which remains to be finished. Especially, the subject to solve the quantum mechanical equation with respect to the collective degrees of freedom for the tilting angles has not been accomplished. In the following, the physical results obtained are summarized.1)The strongly-coupled rotational one-quasiparticle bands, based on the orbits with the high-angular momentum component with respect to the symmetry axis, has been investigated in terms of the tilted axis cranking method. It is found that the problem of underestimating the angular frequency of starting tilting point is nicely sovled by including the quadrupole residual interaction, especially its K=1 component.2)The recently observed wobbling rotational band excited on the triaxial superdeformated band in Hf, Lu nuclei has been studied by using the random-phase-approximation. If assuming the positive-gamma triaxial deformation, one cannot expect the wobbling motion because of the irrotational behavior of three moments of inertia. It is, however; clarified that the quasiparticle alignment, inherent in the microscopic random-phase-approximation calculation, changes the ratio of three moments of inertia from their irrotational behavior, and then the wobbling motion became possible to exist.