Convariant single-time bound-state equation

We derive a system of covariant single-time equations for a two-body bound state B ∼ (φ1φ2) in a model of scalar fields φ1 and φ2 interacting via exchange of another scalar field χ. The derivation of the system of equations follows from the Haag expansion. The equations are linear integral equations that are explicitly symmetric in the masses, m1 and m2, of the scalar fields, φ1 and φ2. We present an approximate analytic formula for the mass eigenvalue of the ground state and give numerical results for the amplitudes for a choice of constituent and exchanged particle masses.