Abstract:Année de publication : 2011
In this manuscript, we review the description of the initial stages of high energy heavy ion collisions in the Color Glass Condensate framework. The primary goal of this work is to provide a first principles approach, based on Quantum Chromo-Dynamics, to the calculation of initial conditions for the subsequent hydrodynamical evolution of the matter produced in heavy ion collisions such as those studied at RHIC or at the LHC. In the first part, we develop some general tools and results that are useful in any quantum field theory coupled to strong external sources. We show how to organize the expansion in powers of the coupling constant in these theories, with a particular emphasis on the simplifications that arise when one considers inclusive observables. In the second part, we apply these techniques to the Color Glass Condensate. We show that the dependence of inclusive observables on the collision energy arises from logarithmic terms that can be factorized into universal distributions that describe the color charge content of high energy nuclei. We then present some phenomenological applications of this factorization theorem, and confront these predictions with measurements performed at RHIC. In the last part, we focus on the final state evolution of the system, with emphasis on the issue of thermalization of the matter produced in heavy ion collisions. Starting from the existence of instabilities in the classical Yang-Mills equations, that lead to secular divergences in observables when higher order corrections are included, we develop a resummation scheme that collects all the dominant secular terms and leads to finite expressions. Finally, we show on the example of a scalar field theory that this resummation has also the virtue of making the system relax towards thermal equilibrium.