Fermionic sign structure of high-order Feynman diagrams in a many-fermion system

Feynman diagrams versus Fermi-gas Feynman emulator

Partial Dynamical Symmetry in a Fermionic Many-body System

The fundamental concept underlying algebraic theories in quantum physics is that of an exact or dynamical symmetry. Realistic quantum systems, however, often require the associated symmetry to be broken in order to allow for a proper description of some observed basic features. Partial dynamical symmetry (PDS) describes an intermediate situation in which some eigenstates exhibit a symmetry whic...

superstring Feynman diagrams

The multi-loop amplitudes for the closed, oriented superstring are represented by finite dimensional integrals of explicit functions calculated through the super-Schottky group parameters and interaction vertex coordinates on the supermanifold. The integration region is proposed to be consistent with the group of the local symmetries of the amplitude and with the unitarity equations. It is show...

Feynman Diagrams in Quantum Mechanics

We explain the use of Feynman diagrams to do perturbation theory in quantum mechanics. Feynman diagrams are a valuable tool for organizing and understanding calculations. We first work several examples for the 1-dimensional harmonic oscillator, and then proceed to justify our calculations.

The two-fermion vector potential of constraint theory from Feynman diagrams

The relativistic fermion-antifermion bound state vector potential of constraint theory is calculated, in perturbation theory, by means of the Lippmann−Schwinger type equation that relates it to the scattering amplitude. Leading contributions of n-photon exchange diagrams are calculated in an approximation scheme that adapts eikonal approximation to the bound state problem. They produce terms pr...