Il Nuovo Cimento (1955-1965)

, 17:809 | Cite as

Sur une méthode simplifiée de calcul pour les processus relativistes en électrodynamique quantique

  • P. Kessler
Article

Riassunto

Proponiamo un metodo semplificato di calcolo approssimato per i processi relativistici in elettrodinamica quantistica. Il nostro punto di partenza è una generalizzazione teorica nel campo quantistico del metodo semiclassico di Williams-Weizsäcker, che definisce uno spettro fotonico equivalente per una particella relativistica carica. Poi mostriamo che si può scrivere una formula del tipo Williams-Weizsäcker per esprimere la probabilità associata ad ogni diagramma elementare contenente due linee di fermioni ed una di fotoni, purchè entrambi gli stati fermionici siano relativistici. Si danno molti esempi di casi in cui questo concetto è applicato per calcolare processi di ordine superiore riferendoli direttamente ad effetti più semplici. I casi trattati sono: 1) bremsstrahlung di una particella relativistica ad un dato angolo; 2) rinculo nucleare per creazione di coppie da fotoni di alta energia; 3) bremsstrahlung interna nella disintegrazione del mesone μ; 4) correzioni radiative negli spettri β di raffronto di12B e12N. In conclusione si discutono brevemente ulteriori possibilità di estendere il metodo (specialmente alla teoria dei mesoni π).

Summary

We propose a simplified method of approximate calculation for relativistic processes in quantum electrodynamics. Our starting point is a quantum field theoretical generalization of the semi-classical Williams-Weizsäcker method, which defines an equivalent photon spectrum for a relativistic charged particle. We then show that a formula of the Williams-Weizsäcker type can be set up to express the probability associated with any elementary diagram containing two fermion lines and one photon line, provided that both fermion states are relativistic. The elementary virtual processes represented by these diagrams may thus be considered as « quasi real processes ». Several examples are given, in which this concept is applied to calculate higher order processes by relating them directly to simpler effects. The cases we treat are: 1) bremsstrahlung of a relativistic particle at a given angle; 2) nuclear recoil from pair creation by high-energy photons; 3) inner bremsstrahlung in the disintegration of the μ-meson; 4) radiative corrections in the compared β-ray spectra of12B and12N. In conclusion, further possibilities to extend the method (especially to π-meson theory) are briefly discussed.

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Copyright information

© Società Italiana di Fisica 1960

Authors and Affiliations

  • P. Kessler
    • 1
  1. 1.Laboratoire de Physique Atomique du Collège de FranceParis

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