A New QCD Correction to Gauge Boson Decay into Heavy Flavor

We find that, at order alpha_s, the partial width of Z^0 to heavy flavors receives a power correction from a novel QCD mechanism, which is not suppressed by inverse powers of M_Z, but only by two unknown O(\lambdaqcd/m) constants. The hadronic W width also receives a similar correction. These parameters may be fitted from the global electroweak analysis, and consequently the Standard Model predictions of various electroweak observables will be updated. This new mechanism is of no help to reconcile the discrepancy in b forward-backward asymmetry. We also point out the implication of this mechanism to heavy flavor production in other collider experiments.