arXiv 0812.05002008-12-02hep-phhep-th

AdS/CFT强耦合等离子体中的部分子和喷流

Partons and jets in a strongly-coupled plasma from AdS/CFT

Edmond Iancu

备注：: 61 pages, 28 figures. Based on lectures presented at the XLVIII Cracow School of Theoretical Physics, `Aspects of duality', Zakopane, Poland, June 13-22, 2008
发表信息：: Acta Phys.Polon.B39:3213-3280,2008

摘要：

我们给出了一个教学审查的最新进展，了解强耦合等离子体在有限温度下的硬探针的响应。等离子体是N=4超对称杨-米尔斯理论的等离子体，硬探针是虚光子，或者更准确地说，是R电流。通过规范/引力对偶，将电流与等离子体相互作用的问题映射到麦克斯韦场与嵌入AdS_5 × S^5几何中的黑洞之间的引力相互作用上。AdS/CFT结果的物理解释可以在紫外/红外对应的帮助下重建。因此，我们推断，对于足够高的能量，光子（或任何其他硬探针：夸克、胶子或介子）通过一种普遍的机制消失在等离子体中，这种机制是准民主部分子分支：电流发展出一个部分子级联，使得在分支过程的任何一步，能量几乎均等地分配给子部分子。分支率由等离子体控制，等离子体以恒定的力~ T^2作用于有色部分子。当在等离子体无限动量框架中重新解释时，相同的AdS/CFT结果表明等离子体结构函数的部分子图像，其中所有部分子都落在非常小的Bjorken x值处。对于真空中的类时电流，准民主分支意味着在强耦合的电子正电子湮没中不应该有喷流，而只有强子物质的空间各向同性分布。

英文摘要：

We give a pedagogical review of recent progress towards understanding the response of a strongly coupled plasma at finite temperature to a hard probe. The plasma is that of the N=4 supersymmetric Yang-Mills theory and the hard probe is a virtual photon, or, more precisely, an R-current. Via the gauge/gravity duality, the problem of the current interacting with the plasma is mapped onto the gravitational interaction between a Maxwell field and a black hole embedded in the AdS_5 x S^5 geometry. The physical interpretation of the AdS/CFT results can be then reconstructed with the help of the ultraviolet/infrared correspondence. We thus deduce that, for sufficiently high energy, the photon (or any other hard probe: a quark, a gluon, or a meson) disappears into the plasma via a universal mechanism, which is quasi-democratic parton branching: the current develops a parton cascade such that, at any step in the branching process, the energy is almost equally divided among the daughter partons. The branching rate is controlled by the plasma which acts on the colored partons with a constant force ~ T^2. When reinterpreted in the plasma infinite momentum frame, the same AdS/CFT results suggest a parton picture for the plasma structure functions, in which all the partons have fallen at very small values of Bjorken's x. For a time-like current in the vacuum, quasi-democratic branching implies that there should be no jets in electron-positron annihilation at strong coupling, but only a spatially isotropic distribution of hadronic matter.

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