Sidi H. Djah, Hanno Gottschalk, Habib Ouerdiane
January 12, 2005
Partition- and moment functions for a general (not necessarily Gaussian) functional measure that is perturbed by a Gibbs factor are calculated using generalized Feynman graphs. From the graphical calculus, a new notion of Wick ordering arises, that coincides with orthogonal decompositions of Wiener-Itô type only if the measure is Gaussian. Proving a generalized linked cluster theorem, we show that the logarithm of the partition function can be expanded in terms of connected Feynman graphs ("linked cluster theorem").
Keywords:perturbation theory, Feynman diagrams, Wick ordering