Classical and quantum coherence in bremsstrahlung

Recent considerations about the importance of coherence effects for bremsstrahlung in dense matter (Landau-Pomerancuk-Migdal-effect) are presented and extended for the application to QCD transport and parton kinetic models. Low energy (soft limit) theorems are discussed and pocket correction formulae for the in-matter radiation cross sections are derived using the experience from an exactly solvable hard-scattering model. In contrast to recent derivations by others the author requires a stronger in-medium suppression factor of the form (ωτ)4/(1+(ωτ)2)2 where ω is the energy of the radiated quantum and τ is the mean free time between successive collisions. This stronger suppression of e.g. gluon radiation implies an even weaker stopping power of high energy partons than discussed by Wang and Gyulassy