Towards a Quantum Transport Description of Particles with finite Mass Width
The effects of the propagation of particles which have a finite life time and an according width in their mass spectrum are discussed in the context of transport descriptions. In the first part the coupling of soft photon modes to a source of charged particles is studied in a classical model which can be solved completely in analytical terms. The solution corresponds to a re-summation of certain field theory diagrams. The second part addresses the derivation of transport equations which also account for the damping width of the particles. The $Φ$-derivable method of Baym is used to derive a self-consistent and conserving scheme. For this scheme a conserved energy-momentum tensor can be constructed. Furthermore, a kinetic entropy can be derived which besides the standard quasi-particle part also includes contributions from fluctuation.