Self-Energies and Rotational Symmetry

The rotational invariance is violated in the lightcone quantization method when the Fock space is truncated for practical calculations. To what extent the rotation symmetry is broken in the lightcone quantization approach can be quantified by calculating the explicit rotation dependence of the two-body scattering phase shifts. We analyze the scattering phase shifts in a simple scalar field model, extending the lightcone ladder approximation to the lowest order lightcone Tamm-Dancoff approximation in which the self-energy corrections are incorporated. We find that the self-energy effects significantly restore the rotation symmetry. Also, these effects make the phase shifts stabilize as the coupling constant grows. This is in a good agreement with the previous bound state results that the self-energy effects are as repulsive as relativistic kinematic corrections and retardation effects.