Tidal stretching of gravitons into classical strings: application to jet quenching with AdS/CFT

Abstract: Previous work has shown that the standard supergravity approximation can break down when using AdS/CFT duality to study certain top-down formulations of the jet stopping problem in strongly-coupled N=4 super-Yang-Mills (SYM) plasmas, depending on the virtuality of the source of the "jet." In this paper, we identify the nature of this breakdown: High-momentum gravitons in the gravitational dual get stretched into relatively large classical string loops by tidal forces associated with the black brane. These stringy excitations of the graviton are not contained in the supergravity approximation, but we show that the jet stopping problem can nonetheless still be solved by drawing on various string-theory methods (the eikonal approximation, the Penrose limit, string quantization in pp-wave backgrounds) to obtain a probability distribution for the late-time classical string loops. In extreme cases, we find that the gravitons are stretched into very long folded strings which are qualitatively similar to the folded classical strings originally used by Gubser, Gulotta, Pufu and Rocha to model the jet stopping problem. This makes a connection in certain cases between the different methods that have been used to study jet stopping with AdS/CFT and gives a specific example of a precise N=4 SYM problem that generates such strings in the gravity description.