## Abstract

The quantum-electrodynamical S matrix is obtained as the set of on-mass-shell values of the renormalized momentum-space Green's functions multiplied by Ci(mi2-pi2)1+i for each particle i, where i is proportional to the fine-structure constant and Ci is a constant. A photon mass is not needed to eliminate virtual infrared divergences. Instead the parameters i=mi2-pi2 regularize Feynman integrals in the infrared region, and the dependence on the i is canceled against the expansion of (mi2-pi2)i multiplying lower-order Green's functions. Exact cross-section formulas are developed which express transition rates in terms of this S matrix. They account for radiation damping nonperturbatively, whereas the S matrix must be calculated perturbatively as a power series in. It is seen that in processes with very small energy loss to unobserved photons individual elements of the quantum-electrodynamical S matrix are directly observable. Rules for practical calculations are summarized.

Original language | English (US) |
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Pages (from-to) | 3504-3530 |

Number of pages | 27 |

Journal | Physical Review D |

Volume | 11 |

Issue number | 12 |

DOIs | |

State | Published - 1975 |

## ASJC Scopus subject areas

- Physics and Astronomy (miscellaneous)