Self-consistent harmonic oscillator model and tilted rotation

The three-dimensional harmonic oscillator model including a cranking term is used for an energy variational calculation. Energy minima are found under variation of the three oscillator frequencies determining the shape of the system for given values of the three components of the rotational vector which determines the orientation of the angular momentum in the intrinsic frame. Tilted rotations are established by numerical means for triaxial nuclei. The onset of tilted rotations is related to an instability of the mean field as verified by the random phase approximation. Analytic expressions are derived for the critical rotational frequencies associated with the mean-field instability.