The three-particle collision term in quantum kinetic theory

J. T. Lowry, William C. Schieve

The relationship between the collision kernel of the three-body quantum mechanical kinetic equation (quantum version of the Choh-Uhlenbeck equation) and modern scattering theory is examined utilizing the work of Faddeev and Weinberg. Recognizing that the collision kernel is related to the M⊘ller scattering operator it is shown that the collision kernel is “well-defined” for suitable interaction potentials and contains only connected three particle collisions in the sense of Weinberg. The collision kernel is interpreted physically and is shown to contain a generalization of the ordinary Boltzmann collision term to three particle processes plus a distorted-wave-impulse approximation correction to the two particle Boltzmann collision term.

Pierre M. V. Résibois

Pierre-Jean Nacher, Geneviève Tastevin, Franck Laloë

We generalize our previous work on the compatibilty of kinetic equations with second virial corrections to the inclusion of spin and particle indistinguishability; the system is supposed to be sufficiently dilute for higher order virial density corrections (interactions and statistics) to be negligible. We show that the general idea of the “free Winger transform” can be extended to this situation; the function which appears in the kinetic equation becomes here a matrix which acts in the space of spin states of the particles. Assuming that the collisions are described by a hamiltonian which does not act on the spins (a very good approximation for nuclear spins), we write explicitly a kinetic equation which is valid for this case. The right hand side of the equation is an 18 dimension integral, as for spinless distinguishable particles, but here it contains an additional term due to statistics, which introduces commutators and anticommutators. We discuss the local conservation laws in this formalism and find, as expected, a total number of 8 conserved quantities for spin 1/2 particles (including three components of the magnetization). When the gas is at equilibrium, we obtain a pressure dependence which is in agreement with known calculations on spin polarized gases. We finally study the gradient expansion of the collision integral, and show that the zero-order (local) part is identical with the 4 terms (including identical spin rotation terms) obtained previously by Lhuillier et al. The first order (non-local) part contains many terms, wich we compare with those obtained by Silin in a context more closely related to the Landau theory.

Pierre M. V. Résibois

Takashi Ikeda

We derive a kinetic equation with a non-Markovian collision term that includes a memory effect from Kadanoff-Baym equations in ${\ensuremath{\varphi}}^{4}$ theory within the three-loop level for the two-particle irreducible effective action. The memory effect is incorporated into the kinetic equation by a generalized Kadanoff-Baym ansatz. Based on the kinetic equations with and without the memory effect, we investigate the influence of this effect on the decay of a single particle excitation with zero momentum in 3+1 dimensions and the spatially homogeneous case. The numerical results show that, while the time evolution of the zero mode is completely unaffected by the memory effect due to a separation of scales in the weak coupling regime, this effect leads first to faster relaxation than the case without it and then to slower relaxation as the coupling constant increases.