Two-body contribution to the relaxation of collective excitations in cold finite Fermi systems
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The two-body contribution to the relaxation of collective excitations in finite Fermi systems has been investigated. Special attention has been given to exploring the effect that the special features of equilibrium distribution functions in such systems may exert on this contribution. The diffuseness and oscillations of the equilibrium distribution function in momentum space have been taken into account together with retardation effects in a collision integral. A potential of the Woods-Saxon form has been used for an equilibrium mean field. It has been shown that oscillations of the equilibrium distribution function lead to a compensation of particle flows in an equilibrium system and to a significant reduction of the relaxation rate because of the diffuseness of the equilibrium distribution function. As a result, the widths of giant quadrupole resonances take values that are close to those that are obtained by taking into account retardation effects in the collision integral and by using the distribution function in the Thomas-Fermi approximation.