Instantons as a bridge between weak and strong coupling in quantum chromodynamics

The transition from weak to strong coupling in quantum chromodynamics is discussed using semiclassical methods to calculate the effective coupling g(a) of an effective lattice theory as a function of a. We demonstrate that the renormalization effects due to instantons cause a sharp transition from weak to strong coupling in the range g(a)1.5-3. This is verified by showing that the "string tension" as well as the function calculated by semiclassical methods match their strong-coupling behavior for g1.5-3. An independent test of this notion is provided by a bag-model calculation of the string tension.