Levinson theorem for Dirac particles in two dimensions

The Levinson theorem for nonrelativistic quantum mechanics in two spatial dimensions is generalized to Dirac particles moving in a central field. The theorem relates the total number of bound states with angular momentum $j$ $(j=\pm \frac{1}{2},\pm \frac{3}{2},\dots )$, $n_j,$ to the phase shifts ${\eta }_j(\pm E_k)$ of scattering states at zero momentum as follows: ${\eta }_j\left(\mu \right)+{\eta }_j(-\mu {)=n}_j\pi$.