Disappearance of quasi-fermions in the strongly coupled plasma from the Schwinger-Dyson equation with in-medium gauge boson propagator

TL;DR

This study non-perturbatively analyzes fermion spectra in a strongly coupled plasma, revealing that in-medium effects cause broadening and eventual disappearance of quasi-fermions, challenging the quasi-particle picture in such conditions.

Contribution

It provides a non-perturbative analysis of fermion spectral functions using Schwinger-Dyson equations with in-medium gauge boson corrections, showing the loss of quasi-fermions at strong coupling.

Findings

Fermion spectral peaks are broadened by in-medium effects.

Peak broadening increases with gauge coupling strength.

No clear fermion peak appears in the strong coupling regime.

Abstract

We non-perturbatively study the fermion spectrum in the chiral symmetric phase focusing on the effects of in-medium corrections for gauge boson. The fermion spectrum is derived by solving the Schwinger-Dyson equation (SDE) with ladder approximation on the real time axis. It is shown that the peak of the fermion spectral function is broadened by in-medium effects for gauge boson compared with the peak obtained with the tree gauge boson propagator. The peak becomes much broader as the value of the gauge coupling increases. This broadening is caused by multiple scatterings of fermions and gauge bosons included through the non-perturbative resummation done by the SDE. In particular, the Landau damping of gauge boson propagator plays an important role in the broadening. Our results show no clear peak in the strong coupling region, implying the disappearance of quasi-fermions in the strongly coupled plasma. This indicates that quasi-particle picture may be no longer valid in the strongly coupled QGP.