Quantum Electrodynamics in the Infinite-Momentum Frame

We examine the formal foundations of quantum electrodynamics in the infinite-momentum frame. We interpret the infinite-momentum limit as the change of variables $\tau =2^{-\frac{1}{1}}\mathrm{}(t+z)\mathrm{}$, $\mathcal{Z}=2^{-\frac{1}{1}}\mathrm{}(t-z)\mathrm{}$, thus avoiding limiting procedures. Starting from the Feynman rules, we derive a $\tau$-ordered perturbation expansion for the $S$ matrix. We then show how this expansion arises from a canonical formulation of the field theory in the infinite-momentum frame. We feel that this approach should lead to convenient approximation schemes for electrodynamics at high energy.