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Résumé |
We present the first AdS/CFT calculation of $\hat q$ for a light quark jet as a function of position or, equivalently, time in a strongly-coupled quark-gluon plasma (QGP). ($\hat q$ is the transverse momentum squared picked up by a high momentum probe per unit length travelled in a QGP.) The $\hat q$ derivation relies on our calculation of the average distance squared, $s^2$, the endpoint of an open string moves while falling in an $AdS_3$-Schwarzschild spacetime. We find that the early time behavior is ballistic, $s^2\sim t^2$, but the late time behavior is the usual diffusive Brownian motion, $s^2\sim t$. These late time dynamics are universal and depend only on the near-horizon physics, which allows us to generalize our results to arbitrary dimensions and thus make contact with the physics explored by RHIC and LHC. As a result, AdS/CFT predicts angular ordering for radiation in medium, just as in vacuum, and in contradistinction to weak-coupling, with its prediction of anti-angular ordering and that AdS/CFT also sensibly predicts a smooth interpolation of angular correlations from light to open heavy flavor in heavy ion collisions. |
