Implications of LEP and SLD data for new physics in Zbb̅ couplings

The combined CERN LEP and SLAC Large Detector (SLD) data on the bb̅ forward-backward asymmetry from the Z-pole measurements may imply the presence of new physics in the Zbb̅ couplings. In general, the effect of new physics can be parametrized by SU_C(3)×SU_L(2)×U_Y(1) invariant higher dimensional operators. By fitting the recently announced LEP and SLD data on A_b and R_b, the size of the coupling strengths of these operators can be determined. We also found that the new physics operators can be divided into two types, depending on their Higgs field content. The ones involving the Higgs field have very mild effects at higher energy colliders, while the other type which do not contain the Higgs field can show significantly large effects on bb̅ production at LEP II, tt̅ production at the NLC and single top quark production at the Fermilab Tevatron. The preliminary data from the LEP II measurements disfavor the second type of operators.