title: Extracting spectral properties from Keldysh Green functions.
abstract: We investigate the possibility to assist the numerically ill-posed calculation of spectral properties of interacting quantum systems in thermal equilibrium by extending the imaginary-time simulation to a finite Schwinger-Keldysh contour. The effect of this extension is tested within the standard maximum entropy approach to analytic continuation. We find that the inclusion of real-time data improves the resolution of structures at high energy, while the imaginary-time data are needed to correctly reproduce low-frequency features such as quasiparticle peaks. As a nonequilibrium application, we consider the calculation of time-dependent spectral functions from retarded Green function data on a finite time interval, and compare the maximum entropy approach to direct Fourier transformation and a method based on Padé approximants.
authors.affiliation: Department of Physics, University of Göttingen, D-37077 Göttingen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Dirks
authors.forename: Martin
authors.initials: M
authors.lastname: Eckstein
authors.forename: Thomas
authors.initials: T
authors.lastname: Pruschke
authors.forename: Philipp
authors.initials: P
authors.lastname: Werner
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D008956:Models, Chemical; D011789:Quantum Theory