Simple connection between covariant Feynman formalism and time-ordered perturbation theory in the infinite-momentum frame

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Abstract
We introduce a parametrization of loop momenta which allows us to perform one of the Feynman integrations in a very transparent way. This leads to expressions which can easily be related to terms resulting from time-ordered perturbation theory in the infinite-momentum frame. To exemplify our method we consider some simple Feynman integrals. As another example we discuss the covariant expressions of Landshoff, Polkinghorne, and Short for the scaling graph and the electromagnetic form factor. We indicate how to substitute the Sudakov parametrization in their work in order to simplify their discussion and to make comparisons with the work of Gunion, Brodsky, and Blankenbecler more convenient. Finally we derive an elegant form of the bound-state Bethe-Salpeter equation in which one of the Feynman integrations is performed.