LITTLE MIRACLES OF SUPERSYMMETRIC EVOLUTION OF GAUGE COUPLINGS

The invention of supersymmetry, almost exactly 25 years ago,(1) change d the face of high energy physics. The idea that the observed low ener gy gauge groups appear due to the process of spontaneous breaking of a single unifying group G is also quite popular. The synthesis of these two elements results in supersymmetric grand unification. I present ( perturbatively) exact results regarding the supersymmetric evolution o f the gauge couplings from the scale of their unification to lower sca les. In particular, it is shown how the heavy mass thresholds can be p roperly taken into account to all orders.