Equivalence of Covariant and Light-Front Perturbation Theory
  Light-Front Field Theory (LFFT) is a good candidate to describe bound states. In LFFT covariance is non-manifest. Burkardt and Langnau claim that, even for scattering amplitudes, rotational invariance is broken. We will take a different path of obtaining rules for light-front time-ordered diagrams. Covariance depends on the choice of a regulator $\alpha$. We need to apply some regularisation scheme to render physical amplitudes finite. This is done by applying minus regularisation. In this process all ambiguities related to the regulator $\alpha$ are removed. Therefore there is equivalence between the perturbative expansions of covariant and LFFT. 
N. C. J. Schoonderwoerd and B. L. G. Bakker (Vrije Universiteit   Amsterdam)