Heavy Fermion Screening Effects and Gauge Invariance

Abstract

We show that the naively expected large virtual heavy fermion effects in low energy processes may be screened if the process under consideration contains external gauge bosons constrained by gauge invariance. We illustrate this by a typical example of the process $γγ\to b \bar{b}$. Phenomenological implications are also briefly indicated.

a miss-print fixed, 7 pages, LaTex, no figures