Theoretical Background

This section presents the physics underlying sft-wick: the MSR path-integral formalism for stochastic differential equations, Wick’s theorem for Gaussian integrals, and the Feynman diagram rules that arise from the perturbative expansion.

Readers already comfortable with MSR perturbation theory may want to skip ahead to the Getting Started tutorial.

• The MSR Formalism
  • From Langevin Equations to Path Integrals
  • Free and Interaction Actions
  • Propagators
  • Itô Convention and Causality
  • Response Phase Convention
  • The Partition Function \(Z=1\)
  • Perturbative Expansion
• Wick’s Theorem
  • Statement
  • Counting Pairings
  • The MSR Constraint
  • Worked Example
  • Low-Level Access
• Feynman Diagram Rules
  • Elements of a Diagram
  • Constructing a Diagram from a Pairing
  • Reading Off Expressions
  • Topological Properties
  • Rendering