Friedrichs Diagrams -- Bosonic and Fermionic

Abstract

We give a mathematically precise review of a diagrammatic language introduced by Friedrichs in order to simplify computations with creation and annihilation operator products. In that language, we establish explicit formulas and algorithms for evaluating bosonic and fermionic commutators. Further, as an application, we demonstrate that the non-linear Hartree dynamics can be seen as a subset of the diagrams arising in the time evolution of a Bose gas.