Regge Daughter Trajectories in the Bethe-Salpeter Equation

Parent and daughter Regge trajectories are found numerically in the scalar Bethe-Salpeter equation with trilinear coupling in the ladder approximation. By using the ordinary partial-wave projection of the scattering amplitude, we obtain the trajectories over a range of energy below threshold; and by projecting the scattering amplitude into 4-dimensional spherical harmonics, we find the slope and intercept of the trajectories at $s=0\mathrm{}$.