A scattering amplitudes approach to hard thermal loops

TL;DR

This paper demonstrates that hard thermal loops in quantum field theories can be derived from classical limits of scattering amplitudes, connecting quantum and classical descriptions without using ghosts.

Contribution

It introduces a novel approach to derive hard thermal loops from classical limits of off-shell currents in QED, QCD, and gravity, avoiding ghosts.

Findings

Hard thermal loops can be obtained from classical limits of off-shell currents.

The approach applies to QED, QCD, and gravity.

Classical wavenumbers are associated with soft particles to reveal classicality.

Abstract

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.