Abstract :
The important parameter μG2 of the heavy quark expansion is analyzed including perturbative and power corrections. The former are found small; a nonperturbative relation is suggested which allows to control power corrections. We conclude that μG2(1 GeV)=0.35+0.03−0.02 GeV2. The effective coupling αs(me)(ω) governing the normalization scale evolution of μG2 is given to two loops. On the nonperturbative side, we advocate the utility of combining the heavy quark expansion with expanding around the “BPS”-type approximation for the meson wavefunction, which implies relations μπ2≈μG2, −ρLS3≈ρD3 and similar ones for the nonlocal correlators.
