Holographic bulk viscosity: GPR vs EO
Alex Buchel, Umut Gursoy, Elias Kiritsis
TL;DR
This paper compares two holographic formulas for bulk viscosity, demonstrating their agreement in complex RG flow theories, thus clarifying their relationship beyond simple scaling cases.
Contribution
It shows that the EO and GPR formulas for holographic bulk viscosity agree in non-trivial RG flow theories, extending previous understanding beyond simple cases.
Findings
EO and GPR formulas agree in N=2* gauge theory plasma
EO and GPR formulas agree in Improved Holographic QCD
The agreement holds in complex RG flow scenarios
Abstract
Recently Eling and Oz (EO) proposed a formula for the holographic bulk viscosity, in arXiv:1103.1657, derived from the null horizon focusing equation. This formula seems different from that obtained earlier by Gubser, Pufu and Rocha (GPR) in arXiv:0806.0407 calculated from the IR limit of the two-point function of the trace of the stress tensor. The two were shown to agree only for some simple scaling cases. We point out that the two formulae agree in two non-trivial holographic theories describing RG flows. The first is the strongly coupled N=2* gauge theory plasma. The second is the semi-phenomenological model of Improved Holographic QCD.
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