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Functional Closure of Schwinger-Dyson Equations in Quantum Electrodynamics, Part 1: Generation of Connected and One-Particle Irreducible Feynman Diagrams
Axel Pelster, Hagen Kleinert, Michael Bachmann
Using functional derivatives with respect to free propagators and interactions we derive a closed set of Schwinger-Dyson equations in quantum electrodynamics. Its conversion to gra…
Recursive Graphical Construction for Feynman Diagrams and Their Weights in Ginzburg-Landau Theory
Hagen Kleinert, Axel Pelster, Bruno Van den Bossche
The free energy of the Ginzburg-Landau theory satisfies a nonlinear functional differential equation which is turned into a recursion relation. The latter is solved graphically ord…
On the Floquet Theory of Delay Differential Equations
Christian Simmendinger, Arne Wunderlin, Axel Pelster
We present an analytical approach to deal with nonlinear delay differential equations close to instabilities of time periodic reference states. To this end we start with approximat…
The Highest-Derivative Version of Variational Perturbation Theory
Bodo Hamprecht, Axel Pelster
We systematically investigate different versions of variational perturbation theory by forcing not only the first or second but also higher derivatives of the approximant with resp…
Variational Perturbation Theory for the Ground-State Wave Function
Axel Pelster, Florian Weissbach
We evaluate perturbatively the density matrix in the low-temperature limit and thus the ground-state wave function of the anharmonic oscillator up to second order in the coupling c…
Recursive Graphical Construction of Tadpole-Free Feynman Diagrams and Their Weights in phi^4-Theory
Axel Pelster, Konstantin Glaum
We review different approaches to the graphical generation of the tadpole-free Feynman diagrams of the self-energy and the one-particle irreducible four-point function. These are n…