### Yuri Kovchegov

Ohio State University
###
Shock Wave Collisions in AdS_5 and in Real Life

We construct a model of high energy heavy ion collisions as two
ultrarelativistic shock waves colliding in AdS_5. Using AdS/CFT
correspondence we argue that this setup corresponds to describing a heavy
ion collision at strong coupling. We argue that expansion of the energy
density of the medium produced in the collision in the powers of proper
time squared corresponds on the gravity side to a perturbative expansion
of the metric in graviton exchanges. We point out that shock waves
corresponding to physical energy-momentum tensors of the nuclei completely
stop almost immediately after the collision in AdS_5, which, on the field
theory side, corresponds to complete nuclear stopping due to strong
coupling effects, likely leading to Landau hydrodynamics. Since in
real-life heavy ion collisions the large Bjorken-x part of nuclear wave
functions continues to move along the light cone trajectories of the
incoming nuclei leaving the small-x partons behind, we conclude that a
pure large coupling approach is not likely to adequately model nuclear
collisions.

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