approach to equilibrium in high energy heavy ion collisions

Abstract : This thesis deals with the theory of the early stages of a heavy ion collision. Just after such a collision, the matter produced -- called the Quark-Gluon-Plasma (QGP) -- has been shown to be far out of thermal equilibrium. One would like to know whether the QGP thermalizes, and what is the typical time scale for this. Proving that the QGP thermalizes would also justify from first principles the hydrodynamical treatment of the subsequent evolution of a heavy ion collision. The manuscript addresses these questions in two different theories. In a first part, we study a scalar field theory. Starting from an out of equilibrium initial condition, one studies the approach to equilibrium in a fixed volume or in a one-dimensional expanding system. In both cases, clear signs of thermalization are obtained. These results are obtained thanks to the classical statistical approximation (CSA), that includes contributions beyond the Leading Order perturbative calculation. In a second part, the Color Glass Condensate -- a quantum chromdynamics (QCD) effective theory well suited to describe the early life of the QGP -- is used to treat more realistically the approach to thermalization in heavy ion collisions. After having derived some analytical prerequisites for the application of the CSA, the numerical simulations performed with the Yang-Mills equations show evidences of an early onset of hydrodynamical behavior of the QGP: the system becomes isotropic on short time scales, while the shear viscosity over entropy ratio is very small, which is characteristic of a quasi perfect fluid.
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Submitted on : Thursday, June 19, 2014 - 3:43:36 PM
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  • HAL Id : tel-01010346, version 1

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Thomas Epelbaum. approach to equilibrium in high energy heavy ion collisions. High Energy Physics - Phenomenology [hep-ph]. Université Pierre et Marie Curie - Paris VI, 2014. English. ⟨tel-01010346⟩

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