Summing infrared singularities in non-abelian gauge theories: The behavior of the exclusive color-singlet quark form factor

The near-mass-shell behavior of the exclusive color-singlet quark form factor is calculated up to the two-loops. In the Landau gauge the result can be expressed as the second order expansion of exp B(p, p′; g² (k²))], where B(p, p′; g²(k²)) is the lowest order contribution evaluated with a gluon propagator of the form (?i/(k² ? iε)) (g_μν ? (k_μk_ν/k²) × g²(k²) being the long-distance invariant charge. This result is valid to all orders, in an order by order near-mass-shell leading logirithm approximation.