Manifest causality in quantum field theory with sources and detectors

Robert Dickinson, Jeff Forshaw, Peter Millington, Brian Cox

Research output: Contribution to journalArticlepeer-review


We introduce a way to compute scattering amplitudes in quantum field theory including the effects of particle production and detection. Our amplitudes are manifestly causal, by which we mean that the source and detector are always linked by a connected chain of retarded propagators. We show how these amplitudes can be derived from a path integral, using the Schwinger-Keldysh “in-in” formalism. Focussing on ϕ 3 theory, we confirm that our approach agrees with the standard S-matrix approach in the case of positive energy plane-wave scattering.
Original languageEnglish
Article number49
Issue number6
Publication statusPublished - 9 Jun 2014


  • High Energy Physics - Phenomenology
  • High Energy Physics - Theory


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