Solutions of a bethe-salpeter equation

We study systematically and exhibit the Lorentz symmetry of the Bethe-Salpeter equation in the light-like case for two scalar quarks of different masses interacting via the exchange of a scalar photon. We develop a new approach for solving the eigenvalue problem of the equation for the general case (not only the light-like). Our method permits accurate analytic expressions for the spectrum and the wave functions.