title: Dielectric function beyond the random-phase approximation: kinetic theory versus linear response theory.
abstract: Calculating the frequency-dependent dielectric function for strongly coupled plasmas, the relations within kinetic theory and linear response theory are derived and discussed in comparison. In this context, we give a proof that the Kohler variational principle can be extended to arbitrary frequencies. It is shown to be a special case of the Zubarev method for the construction of a nonequilibrium statistical operator from the principle of the extremum of entropy production. Within kinetic theory, the commonly used energy-dependent relaxation time approach is strictly valid only for the Lorentz plasma in the static case. It is compared with the result from linear response theory that includes electron-electron interactions and applies for arbitrary frequencies, including bremsstrahlung emission. It is shown how a general approach to linear response encompasses the different approximations and opens options for systematic improvements.
authors.affiliation: Universität Rostock, Institut für Physik, 18051 Rostock, Germany. heidi.reinholz@uni-rostock.de
authors.forename: H
authors.initials: H
authors.lastname: Reinholz
authors.forename: G
authors.initials: G
authors.lastname: Röpke