Shining a Gluon Beam Through Quark-Gluon Plasma

TL;DR

This paper calculates how a gluon beam emitted by a rotating quark in a strongly coupled plasma is rapidly quenched, shedding sound waves and resembling jet quenching phenomena observed in heavy ion collisions.

Contribution

It provides a detailed analysis of gluon radiation and attenuation in strongly coupled plasma using holographic methods, revealing the behavior of gluon beams and sound wave production.

Findings

High-momentum gluon beams are rapidly attenuated in plasma.

Gluon radiation produces trailing sound waves that thermalize quickly.

The angular distribution of the gluon beam remains unchanged during attenuation.

Abstract

We compute the energy density radiated by a quark undergoing circular motion in strongly coupled $\mathcal N = 4$ supersymmetric Yang-Mills plasma. If it were in vacuum, this quark would radiate a beam of strongly coupled radiation whose angular distribution has been characterized and is very similar to that of synchrotron radiation produced by an electron in circular motion in electrodynamics. Here, we watch this beam of gluons getting quenched by the strongly coupled plasma. We find that a beam of gluons of momenta $\sim q \gg \pi T$ is attenuated rapidly, over a distance $\sim q^{1/3} (\pi T)^{-4/3}$ in a plasma with temperature $T$. As the beam propagates through the plasma at the speed of light, it sheds trailing sound waves with momenta $\lesssim \pi T$. Presumably these sound waves would thermalize in the plasma if they were not hit soon after their production by the next pulse of gluons from the lighthouse-like rotating quark. At larger and larger $q$, the trailing sound wave becomes less and less prominent. The outward going beam of gluon radiation itself shows no tendency to spread in angle or to shift toward larger wavelengths, even as it is completely attenuated. In this regard, the behavior of the beam of gluons that we analyze is reminiscent of the behavior of jets produced in heavy ion collisions at the LHC that lose a significant fraction of their energy without appreciable change in their angular distribution or their momentum distribution as they plow through the strongly coupled quark-gluon plasma produced in these collisions.