A universal fermionic analogue of the shear viscosity

TL;DR

This paper holographically computes supercharge diffusion constants in supersymmetric theories, extending previous work to M2- and M5-branes, and establishes a universal relation akin to the viscosity to entropy ratio.

Contribution

It introduces a universal fermionic analogue of shear viscosity and relates diffusion constants to fermionic absorption cross sections in diverse supersymmetric theories.

Findings

Derived diffusion constants via correlator poles of supersymmetry currents

Calculated diffusion constants using dual gravitino modes and a new Kubo formula

Provided evidence for generalized dimensional reduction applicability for fermions

Abstract

We holographically compute supercharge diffusion constants in supersymmetric field theories, dual to AdS black brane solutions of arbitrary dimension. This includes the extension of earlier work by Kontoudi and Policastro for D3-branes to M2- and M5-brane theories. We consider the case of vanishing chemical potential. In particular, we relate the product of a diffusion constant and the energy density to a universal result for the fermionic absorption cross section. This relation is analogous to the famous proof of universality of $\eta / s$. We calculate the diffusion constants in two different ways: First, the computation is performed via the low frequency, low momentum pole of the correlator of supersymmetry currents. This pole describes the hydrodynamic phonino mode, the massless Goldstone fermion of spontaneous supersymmetry breaking by temperature. Second, the calculation is carried out using the dual transversal mode of the bulk gravitino, with the help of a new Kubo formula. Moreover, we provide some evidence for the applicability of generalized dimensional reduction for fermions when computing the corresponding D$p$-brane diffusion constants.