Relativistic reduced mass and quasipotential equation

A definition of a relativistic reduced mass is introduced on the basis of the Logunov–Tavkhelidze equation. A local quasipotential equation of Shrödinger type is obtained for the description of bound systems of two particles of arbitrary spins. The bound system spectrum is investigated in the case of scalar and vector Coulomb interaction. Various definitions of the relativistic reduced mass are discussed.