Treatment of the infrared contribution: NLO QED evolution as a pedagogic example

Understand

We show that the conventional prescription used for DGLAP parton evolution at NLO has an inconsistent treatment of the contribution from the infrared (IR) region.

• We illustrate the problem by studying the simple example of QED evolution, treating the electron and photon as partons.
• The deficiency is not present in a physical approach which removes the IR divergency and allows calculation in the normal 4-dimensional space.