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arXiv 2008.11685hep-thastro-ph.COcond-mat.otherhep-phmath-phmath.MP
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大N展开与弦论的非平衡态

Large-N Expansion and String Theory Out of Equilibrium

Petr Horava, Christopher J. Mogni

摘要:

我们分析了一般非平衡系统的波动矩阵自由度和$SU(N)$对称性的大- $N$扩展,使用Schwinger-Keldysh形式主义和它的封闭的实时轮廓的向前和向后的组件。在平衡状态下,这种系统的大- $N$展开导致拓扑复杂性不断增加的二维表面拓扑的总和,预测了用弦论进行对偶描述的可能性。我们把这个论证从平衡态扩展开来,研究了对偶弦论中拓扑展开的普适特征。我们的结论是,在非平衡弦微扰理论中,世界片拓扑的求和被进一步细化:每个世界片表面$Σ$经历三重分解,分解为对应于时间轮廓的前向分支的部分$Σ^+$,对应于时间轮廓的后向分支的部分$Σ^-$,以及对应于时间轮廓的两个分支相遇的遥远未来的时刻的部分$Σ^\wedge$。拓扑上的和变成了三重分解上的和。我们将我们的研究结果推广到Kadanoff-Baym时间轮廓相关的系统在有限的温度下,和封闭和开放的情况下,定向或无定向字符串。我们的结果是普遍的,并遵循唯一的大$N$扩展的功能,没有任何假设的世界面动力学。

英文摘要:

We analyze the large-$N$ expansion of general non-equilibrium systems with fluctuating matrix degrees of freedom and $SU(N)$ symmetry, using the Schwinger-Keldysh formalism and its closed real-time contour with a forward and backward component. In equilibrium, the large-$N$ expansion of such systems leads to a sum over topologies of two-dimensional surfaces of increasing topological complexity, predicting the possibility of a dual description in terms of string theory. We extend this argument away from equilibrium, and study the universal features of the topological expansion in the dual string theory. We conclude that in non-equilibrium string perturbation theory, the sum over worldsheet topologies is further refined: Each worldsheet surface $Σ$ undergoes a triple decomposition into the part $Σ^+$ corresponding to the forward branch of the time contour, the part $Σ^-$ on the backward branch, and the part $Σ^\wedge$ that corresponds to the instant in the far future where the two branches of the time contour meet. The sum over topologies becomes a sum over the triple decompositions. We generalize our findings to the Kadanoff-Baym time contour relevant for systems at finite temperature, and to the case of closed and open, oriented or unoriented strings. Our results are universal, and follow solely from the features of the large-$N$ expansion without any assumptions about the worldsheet dynamics.

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