Shear Viscosities of Photons in Strongly Coupled Plasmas

TL;DR

This paper studies the shear viscosity of thermal photons in quark-gluon plasma and super Yang-Mills plasma, revealing how it varies with coupling strength and temperature, with implications for understanding strongly coupled plasmas.

Contribution

It provides a comparative analysis of photon shear viscosity at different couplings in QGP and SYMP, highlighting the suppression at strong coupling and behavior near deconfinement.

Findings

Photon shear viscosity decreases with increasing coupling strength.

Shear viscosity increases rapidly near the deconfinement transition.

Photon spectrum blue-shifts at strong coupling, affecting viscosity.

Abstract

We investigate the shear viscosity of thermalized photons in the quark gluon plasma (QGP) at weak coupling and $\mathcal{N}=4$ super Yang-Mills plasma (SYMP) at both strong and weak couplings. We find that the shear viscosity due to the photon-parton scattering up to the leading order of electromagnetic coupling is suppressed when the coupling of the QGP/SYMP is increased, which stems from the blue-shift of the thermal-photon spectrum at strong coupling. In addition, the shear viscosity rapidly increases near the deconfinement transition in a phenomenological model analogous to the QGP.