sdg Interaction boson model : hexadecupole degree of freedom in nuclear structure

The sdg interacting boson model (sdgIBM), which includes monopoles (s), quadrupole(d) and hexadecupole(g) degrees of freedom, enables one to analyze hexadecupole (E4) properties of atomic nuclei. Various aspects of the model, both analytical and numerical, are reviewed emphasizing the symmetry structures involved. A large number of examples are given to provide understanding and tests, and to demonstrate the predictiveness of the sdg model. Extensions of the model to include proton-neutron degrees of freedom and fermion degrees of freedom (appropriate for odd mass nuclei) are briefly described. A comprehensive account of sdgIBM analysis of all the existing data on hexadecupole observables (mainly in the rare-earth region) is presented, including β4 (hexadecupole deformation) systematics, B(IS4; 0GS+→47+) systematics that give information about hexadecupole component in γ-vibration, E4 matrix elements involving few low-lying 4+ levels, E4 strength distributions and hexadecupole vibrational bands in deformed nuclei. (author). 282 refs., 27 figs., 4 tabs