THE EFFECT OF NEW PHYSICS ON RB=GAMMA(Z-]B(B)OVER-BAR) GAMMA(Z-]HADRONS)/

Motivated by the similar to 2 sigma discrepancy between the experiment al value for R(b) and the theoretical prediction of the Standard Model , we examine the effect of new physics on the Z-b-($) over bar b verte x. Using general results for both new scalars and gauge bosons, we sho w that two conditions must be satisfied in order for new physics to gi ve observable deviations in the vertex. In particular, the fermion in the loop must transform chirally under SU(2) x U(1) and it must be mas sive compared to the exchanged boson. We examine the implications of t hese results on the 2 Higgs Doublet model and the Left-Right Symmetric model.