Structure of a thermal quasifermion in the QCD/QED Medium

TL;DR

This study nonperturbatively analyzes thermal quasifermions in QCD/QED media, revealing that their thermal mass diminishes with increasing coupling and disappears in strong coupling, challenging previous quasiparticle models.

Contribution

It provides the first nonperturbative analysis showing the thermal mass vanishes at strong coupling and explores the persistence of decay widths and ultrasoft modes in the medium.

Findings

Thermal mass decreases with coupling strength and vanishes in strong coupling.

Decay width remains large, making quasiparticles hard to observe.

Ultrasoft fermionic mode exists in weakly coupled plasma.

Abstract

In this paper we carried out a nonperturbative analysis of a thermal quasifermion in the chiral symmetric thermal QCD/QED medium by studying its self-energy function through the Dyson-Schwinger equation with the hard-thermal-loop resummed improved ladder kernel. Our analysis reveals several interesting results, two in some of which may force us to change the image of thermal quasifermions: (1) The thermal mass of a quasifermion begins to decrease as the strength of the coupling gets stronger and finally disappears in the strong coupling region, thus showing a property of a massless particle, and (2) its imaginary part (i.e., the decay width) persists to have $O(g^2T \log(1/g))$ behavior. These results suggest that in the recently produced strongly coupled quark-gluon plasma, the thermal mass of a quasiquark should vanish. Taking into account the largeness of the imaginary part, it seems very hard for a quark to exist as a qausiparticle in the strongly coupled quark-gluon plasma phase. Other important findings are as follows: (3) The collective plasmino mode disappears also in the strongly coupled system, and (4) there exists an ultrasoft third peak in the quasifermion spectral density at least in the weakly coupled QED/QCD plasma, indicating the existence of the ultrasoft fermionic mode.