Reduction of the Bethe-Salpeter equation for the scattering amplitude of   the particles with spin 1 to system of the integral equations for invariant   functions
  Bethe-Salpeter equation for the massive particles with spin 1 is considered. The scattering amplitude decomposition of the particles with spin 1 by relativistic tensors is derived. The transformation coefficients from helicity amplitudes to invariant functions is found. The integral equations system for invariant functions is obtained and partial decomposition of this system is performed. Equivalent system of the integral equation for the partial helicity amplitudes is presented. 
A. Yu. Loginov, V. N. Stibunov (Nuclear Physics Institute at Tomsk   Polytechnical University)