String-theory calculations of quark drag
DOI: 10.1063/1.4797346
When two very heavy nuclei smash together forcefully enough, theorists expect the nucleons’ constituents to become unbound and form a quark-gluon plasma. An individual quark traversing the plasma would interact strongly with it and experience a friction-like retarding force. Several recent papers have presented first-principles calculations of parameters associated with such quark drag. All of them employ gauge-string duality, which takes a problem in a suitable strongly interacting gauge theory and converts it to a problem in a weakly interacting gravity theory. The most extensive of the papers is by Christopher Herzog and his colleagues. Some results of that paper have been obtained independently by Steven Gubser and by Jorge Casalderrey-Solana and Derek Teaney. A fourth paper, by Hong Liu and colleagues, focuses on the so-called jet quenching parameter and, alone among the four papers, considers light quarks. All four papers calculate quark damping in a supersymmetric theory that, unlike quantum chromodynamics, is amenable to dualization. Optimistically, one could hope that results obtained from the supersymmetric theory would capture the essence of a true QCD calculation. Encouragingly, the theoretically derived parameters roughly agree with those deduced from experiments at Brookhaven’s Relativistic Heavy Ion Collider. (C. P. Herzog et al., J. High Energy Phys. 07 , 013, 2006 http://dx.doi.org/10.1088/1126-6708/2006/07/013 ;
