Finite width effects and gauge cancellations in W- and Z-boson production in framework of modified perturbation theory

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  • 17 February 2000
Abstract
The processes of unstable W- and Z-boson production are considered in a recently proposed modified perturbation theory (PT), based on direct expansion of probabilities instead of amplitudes. In such an approach the nonintegrable singularities in the phase space, which are intrinsic in the conventional PT, appear as singularities in the coupling constant (with subsequent compensation by the decay factors of unstable states). In present paper the systematic research of the modified PT is carried out. The results are compared with the results of the usual approach, based on calculation of the amplitude with Dyson resummation. The solution of the problem of reducing one-loop PT order in the resonance region, leading to paradoxical results in the usual approach, is discovered. On the basis of this solution the proof of gauge cancellations in any order of the modified PT is given. It is shown that within the given accuracy limits the results obtained in the modified PT may be reproduced in the usual approach with addition of an anomalous term to the probability. An elementary generalization of the fermion-loop scheme is established which provides the complete description of W-pair production in the next-to-leading approximation.

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