Power corrections and gradient expansion in QED transport theory

Abstract

The hard thermal loop (HTL) effective field theory of QED can be derived from the classical limit of transport theory, corresponding to the leading term in a gradient expansion of the quantum approach. In this paper, we show that power corrections to the HTL effective Lagrangian of QED can also be obtained from transport theory by including higher orders in such gradient expansion. The gradient expansion is increasingly infrared (IR) divergent, but the correction that we compute is IR finite. We employ dimensional regularization, and show that this result comes after a cancellation of divergencies between the vacuum and medium contributions. While the transport framework is an effective field theory of the long distance physics of the plasma, we show that it correctly reproduces the correct QED ultraviolet divergencies associated with the photon wave function renormalization.