On the Beaming of Gluonic Fields at Strong Coupling

TL;DR

This paper investigates how gluonic fields emitted by a heavy quark at strong coupling can form collimated beams, using AdS/CFT correspondence, and identifies the conditions under which this beaming occurs.

Contribution

It demonstrates that gluonic beaming at strong coupling results from the string's proximity to the boundary during ultra-relativistic motion, clarifying the underlying mechanism.

Findings

Beaming occurs when the string stays close to the AdS boundary during ultra-relativistic motion.

The approximation involving shock wave formation is valid only for specific quark trajectories.

The conditions for beaming are not generally satisfied for arbitrary quark motions.

Abstract

We examine the conditions for beaming of the gluonic field sourced by a heavy quark in strongly-coupled conformal field theories, using the AdS/CFT correspondence. Previous works have found that, contrary to naive expectations, it is possible to set up collimated beams of gluonic radiation despite the strong coupling. We show that, on the gravity side of the correspondence, this follows directly (for arbitrary quark motion, and independently of any approximations) from the fact that the string dual to the quark remains unexpectedly close to the AdS boundary whenever the quark moves ultra-relativistically. We also work out the validity conditions for a related approximation scheme that proposed to explain the beaming effect though the formation of shock waves in the bulk fields emitted by the string. We find that these conditions are fulfilled in the case of ultra-relativistic uniform circular motion that motivated the proposal, but unfortunately do not hold for much more general quark trajectories.