Gauge technique for heavy quarks

It is possible to determine an off-shell propagator for heavy quarks to order 1/m in mass and in any covariant gauge ξ, which applies universally to all the quarks, by using the gauge technique. Given a simple ansatz for the gluon propagator, the result for the leading behavior of the quark propagator is S(v·k) = Γ(1 + 2αξ)[(1 + γ·v)/2v·k](-v·k/Λ)2αξ 0 F2[1 + αξ,3/2 + αξ; αξ(v·k)2/3πΛ2], where v is the velocity of the particle containing the heavy quark, Λ is a QCD mass scale, and αξ≡ -α(2 + ξ)/3π. The above result is a totally reliable deduction from the assumed gluon propagator in the infrared limit (∼ 1/q2) and accounts for soft-gluon corrections for the fermion in internal loops.