Mixed-symmetry states in nuclei

Properties of a new class of collective states with mixed-symmetry character is the proton-neutron variables are discussed and reviewed. A detailed discussion in terms of F-spin symmetry within the proton-neutron interacting boson model is given. Other approaches such as the two-fluid collective model, the shell-model and microscopic Random-Phase Approximation (RPA) calculations in a deformed potential are also presented. Some concluding remarks on future prospects are made