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

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 [1, 2, 3]. 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 = 250MeV. This estimate should be regarded as preliminary because of the difficulties of comparing two such different theories.