Comparing the drag force on heavy quarks in N=4 super-Yang-Mills theory and QCD

TL;DR

This paper compares the drag force experienced by heavy quarks in strongly coupled N=4 super-Yang-Mills theory and QCD, estimating relaxation times in quark-gluon plasma and discussing the challenges of such comparisons.

Contribution

It provides a comparative analysis of drag forces in N=4 SYM and QCD, normalizing coupling strengths and estimating quark relaxation times in plasma.

Findings

Relaxation time for charm quarks is roughly 2 fm/c at T=250 MeV.

Comparison highlights differences and similarities between N=4 SYM and QCD.

Preliminary estimate due to theoretical differences.

Abstract

Computations of the drag force on a heavy quark moving through a thermal state of strongly coupled N=4 super-Yang-Mills theory have appeared recently in hep-th/0605158, hep-ph/0605199, and hep-th/0605182. I compare the strength of this effect between N=4 gauge theory and QCD, using the static force between external quarks to normalize the 't Hooft coupling. Comparing N=4 and QCD at fixed energy density then leads to a relaxation time of roughly 2 fm/c for charm quarks moving through a quark-gluon plasma at T=250 MeV. This estimate should be regarded as preliminary because of the difficulties of comparing two such different theories.