H. Mansour$^2$ and T. Harko$^3$\
    [$^1$Egyptian Center for Theoretical Physics (ECTP), MTI University, Cairo-Egypt]{}\
    [$^2$Department of Physics, Faculty of Science, Cairo University, Giza-Egypt]{}\
    [$^3$Department of Physics and Center for Theoretical and Computational Physics,]{}\
    [University of Hong Kong, Hong Kong]{}\
title: |
    \
    Viscous Quark-Gluon Plasma in the Early Universe
---

Introduction {#sec:intro}
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The dissipative effects, including both bulk and shear viscosity, are supposed to play a very important role in the early evolution of the Universe. The first attempts at creating a theory of relativistic fluids were those of Eckart [@Ec40] and Landau and Lifshitz [@LaLi87]. These theories are now known to be pathological in several respects. Regardless of the choice of equation of state, all equilibrium states in these theories are unstable and in addition signals may be propagated through the fluid at velocities exceeding the speed of light. These problems arise due to the first order nature of the theory, that is, it considers only first-order deviations from the equilibrium leading to parabolic differential equations, hence to infinite speeds of propagation for heat flow and viscosity, in contradiction with the principle of causality. Conventional theory is thus applicable only to phenomena which are quasi-stationary, i.e. slowly varying 