A Global Fit of LEP/SLC Data with Light Superpartners

We find that re-analyzing the LEP/SLC data with light superpartners and low $\alpha_s(\mz^2)\simeq 0.112$ yields a better fit to the data than the Standard Model, giving a satisfactory description of the $R_b$ measurement, and a better fit to $A_{LR}$. A large body of low energy ($q^2 \ll \mz^2$) data and analyses provide compelling evidence for $\alpha_s(\mz^2)\simeq 0.112$. Global fits to LEP/SLC data in the Standard Model, however, converge on a value of $\alpha_s(\mz^2)\simeq 0.126$. Recently it has become increasingly clear that these should be viewed as incompatible rather than values that can be averaged. We investigate the possibility that new physics is causing the LEP high value. To this end we have conducted a global analysis of LEP/SLC data in the Standard Model and also in the Minimal Supersymmetric Standard Model. Several predictions could confirm (or rule out) the results of this paper: light chargino and stop, top decays into stop and neutralino, large $R_b$, large $A_{LR}$, and a higher $M_W$. We briefly discuss the implications of low $\alpha_s$ for more fundamental high-scale supersymmetric theories.