Bounds on new physics from the new data on parity violation in atomic cesium

We assume the latest experimental determination of the weak charge of atomi c cesium and analyze its implications for possible new physics. We notice t hat the data would imply positive upper and lower bounds on the new physics contribution to the weak charge, delta(N)Q(W). The required new physics sh ould be of a type not severely constrained by the high energy precision dat a. A simplest possibility would be new neutral vector bosons almost un-mixe d to the Z and with sizeable couplings to fermions. The lower positive boun d would however forbid zero or negative delta(N)Q(W) and exclude at 99% CL not only the standard model but also models with sequential Z', in particul ar simple-minded towers of Z-like excitations from extra-dimensions. The bo und would also imply an upper limit on the Z' mass within the models allowe d. Conclusions are also derived for models of four-fermion contact interact ions, (C) 1999 Published by Elsevier Science B.V. All rights reserved.