Two complex problems on the lattice: transport coefficients and finite chemical potential

Abstract

After a few remarks about the problem of extracting transport coefficients from lattice QCD calculations, I report on recent developments in applying stochastic quantization and complex Langevin dynamics to field theories with a complex action due to a nonzero chemical potential. First results demonstrate that the sign problem poses no obstacle for this approach, even in the thermodynamic limit. I conclude with a comparison of two simple one-link models, describing a euclidean system at finite chemical potential and a Minkowski system in real time.

Comments: Invited talk at Strong and Electroweak Matter, Amsterdam, the Netherlands, 26-29 August 2008, 8 pages, 10 eps figures