Eikonal Approximation and the Light Cone

This comment considers the high-energy behavior of a particle of arbitrary spin interacting with an external potential A_μ₁⋯μₙ(x) by means of a J^μ₁⋯μₙA_μ₁⋯μₙ(x) interaction, where J^μ₁⋯μₙ is a function of the fields and their derivatives. It is shown that in the eikonal approximation, "exponentiation" occurs when the light-cone commutation relations satisfy ${∫}{{-}{∞}}^{{∞}}{dx}^{{-}}{∫}{{-}{∞}}^{{∞}}{dy}^{{-}}{[{J}^{+{⋯}+}(x),{J}^{+{⋯}+}(y)]}_{{x}⁺={y}⁺=0}=0.$