LOOP CORRECTIONS TO THE SPHALERON TRANSITION RATE IN THE MINIMAL STANDARD MODEL

The baryon number dissipation rate due to sphaleron transitions at hig h temperatures in the minimal standard model is evaluated. We find tha t this rate can be considerably suppressed by one loop contributions o f bosonic and fermionic fluctuations which are particularly important for a small mass of the Higgs boson and a large top quark mass. Fixing the latter to its recently stated value of 174 GeV the complete erasu re of the baryon asymmetry is prevented within the framework of the mi nimal standard model if the Higgs mass is less than about 63 GeV.