AdS/CFT duality and hard processes

Up to now, the AdS/CFT duality has been used to model thermal transport processes in a strongly coupled gauge plasma (see the Review in this VJ). It was unclear what theories with an AdS/CFT dual predict for hard processes, for which QCD permits rigorous calculations. In several recent articles,

Hatta et al. have shown how such processes can be explored in strongly coupled super-Yang Mills theories with a gravity dual. The authors couple a localized color-singlet current to the Minkowski space boundary of the thermal AdS5 space-time and study how it propagates into the bulk. The spread into the bulk represents the quantum mechanical spread of the orininally localized probe. The explicit solution permits a complete study of the space-time response of the thermal medium as a function of the energy and virtuality of the probe, including all quantum effects at strong coupling. For example, the authors are able to map out in detail how a jet fragments and ultimately disappears into the thermal medium.

This work opens the door to a complete study of hard processes, akin to deep-inelastic scattering and jet formation and quenching, in the gauge theories with a gravity dual. It will be interesting to see how the results map onto the formalism of perturbative QCD in the presence of a medium. It will also be interesting to find out which of the observed features are characteristic of strong coupling, in general, and which ones are peculiar to a theory without asymptotic freedom.

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