2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/129983A new approach to the two-body problem based on the extension of the $SL(2,C)$ group to the $Sp(4,C)$ one is developed. The wave equation with the Lorentz-scalar and Lorentz-vector potential interactions for the system of one spin-1/2 and one spin-0 particle with unequal masses is constructed.Talk given at International School-Seminar "New physics and QCD at external conditions" (Dniepropetrovsk, Ukraine, May 3-6, 2007); 8 pages; prepared for publication in ProceedingsHigh Energy Physics - Theorytext