Massive Fermionic Corrections to the Heavy Quark Potential Through Two   Loops
  A physically defined effective charge can incorporate quark masses analytically at the flavor thresholds. Therefore, no matching conditions are required for the evolution of the strong coupling constant through these thresholds. In this paper, we calculate the massive fermionic corrections to the heavy quark potential through two loops. The calculation uses a mixed approach of analytical, computer-algebraic and numerical tools including Monte Carlo integration of finite terms. Strong consistency checks are performed by ensuring the proper cancellation of all non-local divergences by the appropriate counterterms and by comparing with the massless limit. The size of the effect for the (gauge invariant) fermionic part of $\alpha_V (q^2,m^2) $ relative to the massless case at the charm and bottom flavor thresholds is found to be of order 33%. 
Michael Melles