Bounds on universal new physics effects from fermion-antifermion production at LEP2

Abstract

We consider lepton-antilepton annihilation into a fermion-antifermion pair at variable c.m. energy. We propose for this process a simple parametrization of the virtual effects of the most general model of new physics of universal type. This parametrization is based on a recent approach, that uses the experimental results of LEP1, SLC as theoretical input. It introduces three functions whose energy dependence is argued to be smooth and, in first approximation, negligible. A couple of representative models of new physics are considered, as a support of the previous claim. Explicit bounds are then derived for this type of new physics from the available LEP2 data, and a discussion is given of the relevance in this respect of the different experimental measurements. The method is then extended to treat the case of two particularly simple models of non universal type, for which it is possible to draw analogous conclusions.