Working directly with probabilities in quantum field theory

Understand

We present a novel approach to computing transition probabilities in quantum field theory, which allows them to be written directly in terms of expectation values of nested commutators and anti-commutators of field operators, rather than squared matrix elements.

• We show that this leads to a diagrammatic expansion in which the retarded propagator plays a dominant role.
• As a result, one is able to see clearly how faster-than-light signalling is prevented between sources and detectors.
• Finally, we comment on potential implications of this approach for dealing with infra-red divergences.