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Analysis of the Z0 Resonant Amplitude in General RξGauges

M. Passera, A. Sirlin

hep-pharXiv:hep-ph/9607253

Abstract

The Z0 resonant amplitude is discussed in general Rξgauges. When the original on-shell definition of the Z0 mass M is employed, a gauge dependence of M emerges in the next-to-leading approximation which, although small, is of the same magnitude as the current experimental error. In the following order of expansion, these unphysical effects are unbounded. The gauge dependence of M disappears when modified, previously proposed definitions of mass or self-energies, are used. The relevance of these considerations to the concept of the mass of unstable particles is pointed out.

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