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 \underline{universal} type. This parametrization is based on a recent approach, that uses the experimental results of LEP1, SLC as theoretical input. It introduces \underline{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 {\it non universal} type, for which it is possible to draw analogous conclusions.