输运系数、膜耦合和极值普适性
Transport coefficients, membrane couplings and universality at extremality
摘要：
本文提出了一种计算高阶导数引力理论全息描述的强耦合场论输运系数零频率极限的有效方法。通过计算离壳拉格朗日密度极点的留数可以得到剪切粘度和电导率等流体力学参数。我们澄清在这个意义上，这些系数可以被认为是在地平线上的有效耦合，并提出解析，沃尔德式的剪切粘度和电导率在一个大类的一般高阶导数拉格朗日公式。我们展示了如何将我们的方法应用于零温度但有限化学势的系统。我们的结果意味着，这样的理论满足$η/s=1/4π$普遍在Einstein-Maxwell部门。同样，零频率限制的实部的电导率为这样的系统被证明是普遍为零，我们推测，在这个部门的高阶导数校正不修改这个结果的所有订单微扰理论。
英文摘要：
We present an efficient method for computing the zero frequency limit of transport coefficients in strongly coupled field theories described holographically by higher derivative gravity theories. Hydrodynamic parameters such as shear viscosity and conductivity can be obtained by computing residues of poles of the off-shell lagrangian density. We clarify in which sense these coefficients can be thought of as effective couplings at the horizon, and present analytic, Wald-like formulae for the shear viscosity and conductivity in a large class of general higher derivative lagrangians. We show how to apply our methods to systems at zero temperature but finite chemical potential. Our results imply that such theories satisfy $η/s=1/4π$ universally in the Einstein-Maxwell sector. Likewise, the zero frequency limit of the real part of the conductivity for such systems is shown to be universally zero, and we conjecture that higher derivative corrections in this sector do not modify this result to all orders in perturbation theory.
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