It is shown that nuclear matter described by quasispin or pseudospin operators may exhibit irreversible behavior, in the sense of modern kinetic theory. With the help of the group-contraction technique, a harmonic oscillator can be associated to the many-body system and it is seen that in the standard Lipkin-Meshkov-Glick model the ground-state phase transition gives rise to a significant change in the spectral properties of the characteristic operators. This fact makes room for the introduction of the microscopic operators of irreversible dynamics. Their meaning and the consequences of their existence are examined and it is seen that the time evolution of the quasispin arrangement closely resembles the approach to equilibrium of a macroscopic system.

NUCLEAR STRUCTURE Operators of irreversible Hamiltonian dynamics; quasispin nuclear matter; group contraction, Lipkin-Meshkov-Glick model; ground-state phase transition; entropy; irreversible approach to equilibrium.

• Received 8 December 1980

DOI:https://doi.org/10.1103/PhysRevC.25.2087