Relativistic NN scattering calculations with Δ degrees of freedom

The Bethe-Salpeter equation for NN-NΔ scattering is extended to include ΔΔ states also. With the exception of ¹S₀, the effects are small for $T=1$ because of dominance by NΔ isobaric states. For $T=0$ the influence is accordingly larger. Also a quasipotential approximation to the Bethe-Salpeter equation is considered. Substantial differences are found. In particular, the quasipotential results are considerably more sensitive to the coupling parameters of the transition interaction. As a result a better fit to existing experimental phase shift parameters is obtained with the Bethe-Salpeter equation.