Langreth Rules: Convolutions and Products
Abstract
In the theory of the contour-ordered Green’s functions, one encounters convolutions and products. The task of this chapter is to obtain the corresponding expressions in terms of the real-time functions. This task is accomplished in terms of the so-called Langreth–Wilkins rules, which are here discussed in detail for convolutions as well as for particle–hole-type and particle–particle-type products. A preliminary introduction to what is referred to as the Keldysh space is also provided.
Fields of Study & Subjects
Quantum many-body systems
Physics of Superconductivity and Magnetism
Theoretical and Computational Physics
Publication details
- Journal / source
- Cambridge University Press eBooks
- Pages
- 96–115
- Publication date
- 6 February 2026
- Document type
- Book chapter