Massless Mode and Positivity Violation in Hot QCD

TL;DR

This paper investigates the effects of electric and magnetic scales on quark excitations at high temperature, revealing a novel massless mode with positivity violation linked to confinement effects in hot QCD.

Contribution

It introduces the discovery of a massless excitation arising from the magnetic scale and demonstrates its positivity violation, highlighting the influence of confinement on quark spectral functions.

Findings

Identification of a massless excitation at high temperature.

Positivity violation in quark spectral functions due to this excitation.

Impact of confinement effects on long-range correlations in hot QCD.

Abstract

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.