Soft modes, resonances, and quantum transport

Effects of the propagation of particles that have a finite lifetime and an according width in their mass spectrum are discussed in the context of tran sport description. First, the importance of coherence effects (Landau-Pomer anchuk-Migdal effect) on the production and absorption of field quanta in n onequilibrium dense matter is considered. It is shown that classical diffus ion and Langevin results correspond to a resummation of certain field-theor y diagrams formulated in terms of full nonequilibrium Green's functions. Ge neral properties of broad resonances in dense and hot systems are discussed in the framework of a self-consistent and conserving Phi -derivable method of Baym by considering the examples of the rho meson in hadronic matter an d the pion in dilute nuclear matter. Further, we address the problem of a t ransport description that properly takes into account the damping width of the particles. The Phi -derivable method generalized to the real-time conto ur provides a self-consistent and conserving kinetic scheme. We derive a ge neralized expression for the nonequilibrium kinetic entropy flow, which inc ludes corrections from fluctuations and mass-width effects. In special case s, an H theorem is proven. Memory effects in collision terms contribute to the kinetic entropy flow that, in the Fermi liquid case, reproduces the fam ous bosonic-type T(3)lnT correction to the specific heat of liquid He-3. Fo r the example of the pion-condensate phase transition in dense nuclear matt er, we demonstrate the important role of the width effects within the quant um transport. (C) 2001 MAIK "Nauka/Interperiodica".