Excitation spectrum in quadrupolar systems

Abstract
The static and dynamic properties of an isotropic quadrupolar system are studied by the method of double-time Green's functions. Using symmetrized equations of motion, a Dyson equation for the single-particle Green's function is obtained. The self-energy is expressed in terms of three-particle Green's functions, which are determined using an effective Hamiltonian, with the exact commutation relations approximated by quasiboson ones. A detailed expression for the lifetime of the elementary excitations is obtained.

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