The Two-Loop Infrared Structure of Amplitudes with Mixed Gauge Groups

Understand

The infrared structure of (multi-loop) scattering amplitudes is determined entirely by the identities of the external particles participating in the scattering.

• The two-loop infrared structure of pure \qcd\ amplitudes has been known for some time.
• By computing the two-loop amplitudes for $\bar{f}\,f\longrightarrow X$ and $\bar{f}\,f\longrightarrow V_1\,V_2$ scattering in an $SU(N)\times SU(M)\times U(1)$ gauge theory, I determine the anomalous dimensions which govern the infrared structure for any massless two-loop amplitude.