Reduction of the Salpeter equation for massless constituents

Abstract

Different from the case of the \nr{} limit, it is shown in this paper that in the ultrarelativistic limit, the $L=j$, $j+1$ wave components are large terms for both state with parity $\eta_P=(-1)^{j}$ and state with parity $\eta_P=(-1)^{j+1}$. Moreover, it is found that the states with parity $\eta_P=(-1)^{j}$ are degenerate with the states with parity $\eta_P=(-1)^{j+1}$ if the Lorentz structure of the interaction between the massless constituents is four-vector or time-component of four-vector. The scalar interaction violates this degeneracy.