KINETIC-PROPERTIES OF A BOSE-EINSTEIN GAS AT FINITE-TEMPERATURE

We study, in the framework of the Boltzmann-Bloch-Nordheim equation (B BN)I the kinetic properties of a boson gas above the Bose-Einstein tra nsition temperature T-c. The BBN equation is solved numerically within an algorithm that we test with exact analytical results for the colli sion rate of a homogeneous system in thermal equilibrium. In the class ical regime (T much greater than T-c), the relaxation time of a quadru polar deformation in momentum space is proportional to the mean free c ollision time tau(relax)(proportional to)tau(coll)(proportional to)T(- 1/2). Approaching the critical temperature, quantum statistic effects become dominant, and the collision rate increases dramatically. Nevert heless, this does not affect the relaxation properties of the gas that depend only on the spontaneous collision term in BBN. The relaxation time becomes tau(relax)(proportional to)(T - T-c)(-1/2), exhibiting a critical slowing down. These phenomena can be experimentally confirmed looking at the damping properties of collective motions induced on tr apped atoms. The possibility to observe a transition from collisionles s (zero-sound) to hydrodynamic (such as first and second-sound) is fin ally discussed.