Thermal field theory at next-to-leading order in the hard thermal loop expansion

Understand

In this paper we study the hard-thermal-loop effective theory at next-to-leading order.

• Standard power-counting predicts that a large number of diagrams, including 2-loop diagrams, may need to be calculated.
• In all of the calculations that have been done however, with the exception of the photon self-energy, the full next-to-leading order contribution can be obtained by calculating only soft 1-loop diagrams with effective lines and vertices.
• It is of interest to know if the photon self-energy is the only exception to this rule, or if there are others, and which ones.