  The collective dynamics of a many-body system is described as a special case
of low-energy quantum dynamics, occurring when the ground state breaks a
continuous symmetry of the Hamiltonian. This approach is applied to the
spontaneous breaking of the rotational symmetry of a nuclear Hamiltonian. It is
shown that the excitation operator of the isovector low-lying angular
oscillations in deformed nuclei is a linear combination between angular
momentum operators, which generate static rotations, and "angle" operators,
which generate the transition to a rotating frame.
