Relativistic complex separable potential for describing the neutron-proton system in $^3S_1$-$^3D_1$ partial-wave state

Within a covariant Bethe-Salpeter approach the relativistic complex separable kernel of the neutron-proton interaction for the coupled $^3S_1^+$-$^3D_1^+$ partial-wave state is constructed. The rank-six separable potential elaborated earlier is real-valued, and therefore makes it possible to describe only the elastic part (phase shifts, low-energy parameters, deuteron properties, etc.) of the elastic neutron-proton scattering. The description of the inelasticity parameter comes out of the imaginary part introduced intthe potential. The complex potential parameters are obtained using the available elastic neutron-proton scattering experimental data up to 1.1 GeV.