Notes on LSZ, i epsilon Prescriptions and Perturbation Theory, in QFT and Cosmology
Abstract
We review the original argument of Lehmann et al (LSZ) that relates the flat space S-matrix to the correlation function of field operators and clarify some confusing issues. Next we discuss the origin of the $iε$ prescriptions following Weinberg, but without assuming that the vacuum is free at asymptotic times. Then we discuss the corresponding argument in inflationary cosmology, emphasizing that unitarity violating contour deformations are unnecessary.
Fields of Study & Subjects
Quantum and Classical Electrodynamics
Black Holes and Theoretical Physics
Particle physics theoretical and experimental studies
Publication details
- Journal / source
- arXiv (Cornell University)
- Publication date
- 24 February 2026
- Language
- EN
- Document type
- Preprint