Scattering amplitudes approach to hard thermal loops

Inspired by recent progress on classical limits of scattering amplitudes, we show that hard thermal loops can be obtained from classical limits of off-shell currents. The classicality of hard thermal loops is made manifest by associating classical wavenumbers to soft particles. We compute the classical limit of these currents in QED, QCD, and gravity. Our proposal does not involve the introduction of ghosts.

Automated summary

Inspired by recent progress on classical limits of scattering amplitudes, this study demonstrates that hard thermal loops can be obtained from classical limits of off-shell currents by associating classical wavenumbers to soft particles. The classicality of hard thermal loops is made manifest without the introduction of ghosts, and the classical limit of these currents is computed in QED, QCD, and gravity.