The spinless relativistic Coulomb problem is the bound-state problem for the spinless Salpeter equation (a standard approximation to the Bethe–Salpeter formalism as well as the most simple generalization of the nonrelativistic Schrödinger formalism towards incorporation of relativistic effects) with the Coulomb interaction potential (the static limit of the exchange of some massless bosons, as ...

We calculate the low-energy parameter S in QCD, which is also known as L10, and the pion decay constant fπ using inhomogeneous Bethe-Salpeter equation in improved ladder approximation. To extract these quantities we calculate the “V − A” two-point function, ΠV V (q 2) − ΠAA(q 2), in space-like region. We obtain S = 0.43 ∼ 0.48, which is about 30% larger than the experimental value. The calculat...