Stirring Strongly Coupled Plasma

TL;DR

This paper investigates the energy loss mechanisms of a rotating test quark in strongly coupled N=4 SYM plasma, revealing a crossover between drag and radiation dominance with interference effects.

Contribution

It introduces a classical gravity calculation to analyze the interplay between drag and radiation energy loss for a rotating quark in strongly coupled plasma.

Findings

Energy loss is governed by drag or radiation depending on parameters.

A crossover regime shows destructive interference between energy loss mechanisms.

Results suggest implications for decelerating quarks in plasma.

Abstract

We determine the energy it takes to move a test quark along a circle of radius L with angular frequency w through the strongly coupled plasma of N=4 supersymmetric Yang-Mills (SYM) theory. We find that for most values of L and w the energy deposited by stirring the plasma in this way is governed either by the drag force acting on a test quark moving through the plasma in a straight line with speed v=Lw or by the energy radiated by a quark in circular motion in the absence of any plasma, whichever is larger. There is a continuous crossover from the drag-dominated regime to the radiation-dominated regime. In the crossover regime we find evidence for significant destructive interference between energy loss due to drag and that due to radiation as if in vacuum. The rotating quark thus serves as a model system in which the relative strength of, and interplay between, two different mechanisms of parton energy loss is accessible via a controlled classical gravity calculation. We close by speculating on the implications of our results for a quark that is moving through the plasma in a straight line while decelerating, although in this case the classical calculation breaks down at the same value of the deceleration at which the radiation-dominated regime sets in.