Dissipative non-Abelian fluids from Scherk-Schwarz dimensional reduction

Abstract

We construct a $d$-dimensional dissipative colored fluid by Scherk--Schwarz reduction of a neutral viscous conformal fluid in $D=d+n$ dimensions on an $n$-dimensional unimodular group manifold. The off-diagonal components of the higher-dimensional stress tensor become non-Abelian color currents, while the higher-dimensional shear tensor induces shear, bulk-like and vector-dissipative structures in the reduced theory. We derive the map for the equation of state, sound speed, color current, entropy current and first-order transport coefficients. In particular, \[ \eta=\ee^{\alpha\varphi}\cosh\xi\,\heta,\qquad \tau=\eta\,\frac{n}{(D-1)(d-1)},\qquad \kappa=\eta\sinh^2\xi . \] We also spell out the hydrodynamic-frame issue induced by dimensional reduction, discuss the status of the internal rapidity field $\xi$, and give a detailed account of how the second law descends from the parent theory, including the roles of temperature-dependent viscosity, non-unimodular groups and possible choices for $\xi$. The construction should be regarded as a toy model for non-Abelian dissipative hydrodynamics with the potential of paving the way to direct phenomenological model of, for example, quark--gluon plasma.