Quantum Electrodynamics pp 162-204 | Cite as

# S-Matrix Theory of Electromagnetic Interactions

## Abstract

The S-matrix theory, as we see it, is a relativistic formulation of interactions of fundamental particles based on their *particle properties* (not fields), that is, the formulation of the laws of physics in terms of the *c*-number scattering matrix elements. The scattering matrix itself is defined in terms of the (free physical) particle properties such as momenta, spin, and other quantum numbers which are numbers labelling the representations and states of symmetry groups. We shall give a precise mathematical definition of “particles” and of “scattering”. There is no need to make a fundamental distinction between the S-matrix theory and the relativistic quantum field theory as they both essentially lead to the same results. In one case the basic analyticity properties of the S-matrix are (partly) derived from field axioms and perturbation theory, and in the other case, partly from unitarity condition and are partly postulated. The difference at this stage is perhaps a practical and didactic one; the S-matrix approach is a more direct, computationally and conceptually simple one, using only quantities very close to observed ones.

## Keywords

Irreducible Representation Massless Particle Electromagnetic Interaction Anomalous Magnetic Moment Reducible Representation## Preview

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## References

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