Massless Mode and Positivity Violation in Hot QCD

Understand

We calculate the quark self-energy at one-loop level at high temperature, taking into account contributions from both the (chromo)electric scale $gT$ and the (chromo)magnetic scale $g^2T$.

• While reproducing standard massive excitations due to the electric scale, we uncover a novel massless excitation ascribable to the magnetic scale.
• The residue of this massless excitation is nonpositive at all temperatures, which consequently gives rise to positivity violation in the quark spectral functions.
• This demonstrates the profound impact of confinement effects on thermal quark collective excitations, which manifest genuine long-range correlations in the system.