Vacuum fluctuations and radiation reaction : identification of their respective contributions

It is generally considered that there exists in quantum radiation theory an indetermination in the separation of the respective effects of vacuum fluctuations and radiation reaction. We show in this paper that such an indetermination can be removed by imposing to the corresponding rates of variation to be Hermitian (this is necessary if we want them to have a physical meaning). Such a procedure is generalized to the case of a small system S interacting with a large reservoir R and allows the separation of two types of physical processes, those where R fluctuates and polarizes S (effects of reservoir fluctuations), those where it is S which polarizes R (effects of self reaction). We apply this procedure to an atomic electron interacting with the radiation field and we then identify the contribution of vacuum fluctuations and self reaction to radiative corrections and spontaneous emission of radiation. The analysis of the results obtained in this way allows us to specify the physical pictures which must be associated with the various radiative processes. J. Physique 43 (1982) 1617-1638 NOVEMBRE 1982, F