Feynman, R. P. (1949) The theory of positrons. Physical Review, 76 (6). pp. 749759. ISSN 0031899X. https://resolver.caltech.edu/CaltechAUTHORS:FEYpr49b

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Abstract
The problem of the behavior of positrons and electrons in given external potentials, neglecting their mutual interaction, is analyzed by replacing the theory of holes by a reinterpretation of the solutions of the Dirac equation. It is possible to write down a complete solution of the problem in terms of boundary conditions on the wave function, and this solution contains automatically all the possibilities of virtual (and real) pair formation and annihilation together with the ordinary scattering processes, including the correct relative signs of the various terms. In this solution, the "negative energy states" appear in a form which may be pictured (as by Stückelberg) in spacetime as waves traveling away from the external potential backwards in time. Experimentally, such a wave corresponds to a positron approaching the potential and annihilating the electron. A particle moving forward in time (electron) in a potential may be scattered forward in time (ordinary scattering) or backward (pair annihilation). When moving backward (positron) it may be scattered backward in time (positron scattering) or forward (pair production). For such a particle the amplitude for transition from an initial to a final state is analyzed to any order in the potential by considering it to undergo a sequence of such scatterings. The amplitude for a process involving many such particles is the product of the transition amplitudes for each particle. The exclusion principle requires that antisymmetric combinations of amplitudes be chosen for those complete processes which differ only by exchange of particles. It seems that a consistent interpretation is only possible if the exclusion principle is adopted. The exclusion principle need not be taken into account in intermediate states. Vacuum problems do not arise for charges which do not interact with one another, but these are analyzed nevertheless in anticipation of application to quantum electrodynamics. The results are also expressed in momentumenergy variables. Equivalence to the second quantization theory of holes is proved in an appendix.
Item Type:  Article 

Additional Information:  ©1949 The American Physical Society. Received 8 April 1949. The author has many people to thank for fruitful conversations about this subject, particularly H. A. Bethe and F. J. Dyson. 
Issue or Number:  6 
Record Number:  CaltechAUTHORS:FEYpr49b 
Persistent URL:  https://resolver.caltech.edu/CaltechAUTHORS:FEYpr49b 
Alternative URL:  http://dx.doi.org/10.1103/PhysRev.76.749 
Usage Policy:  No commercial reproduction, distribution, display or performance rights in this work are provided. 
ID Code:  3520 
Collection:  CaltechAUTHORS 
Deposited By:  Tony Diaz 
Deposited On:  12 Jun 2006 
Last Modified:  02 Oct 2019 23:04 
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