Color-glass condensate

About: Color-glass condensate is a research topic. Over the lifetime, 885 publications have been published within this topic receiving 35169 citations.

The CGC and the Glasma: Two Lectures at the Yukawa Institute

Abstract: These lectures present the theory of the Color Glass Condensate (CGC) and the Glasma in an elementary and intuitive manner. This matter controls the high energy limit of QCD. The CGC is the universal limit for the components of a hadron wavefunction important for high energy scattering processes. It is a highly coherent, extremely high energy density ensemble of gluon states. The Glasma is matter produced in the collision of CGCs of two hadrons. It has properties much different from those of the CGC, and is produced in a very short time after the collision. It eventually evolves from the the Color Glass Condensate initial conditions into a Quark Gluon Plasma. We can visualize the collision of two high energy hadrons as shown in Fig. 1. Before the collision, two hadrons appear as Lorentz contracted sheets approaching one another at near light speed. These we will later describe as two sheets of Colored Glass. In a very short time, the sheets of Color Glass interpenetrate one another. This we think of as the initial singularity for the collision. This is of course not a real singularity for finite collision energy, but we will see it becomes one in the limit of infinite energy. After the initial singularity, a Glasma is formed. This is composed of highly coherent gluon fields of very high energy density. If we imagine that the sheets of Colored Glass have passed through one another largely intact, the Glasma forms in the region between the receding sheets. As time goes on, the Glasma evolves into a Quark Gluon Plasma, and eventually into a gas of ordinary hadrons. These lectures are about the earliest stages of these collisions, and will describe neither the Quark Gluon Plasma nor the Hadron Gas. I will motivate the CGC and Glasma from simple physical considerations, and provide a sketchy derivation from QCD. There will be some discussion of experimental tests of these ideas.

Iron Air collision with high density QCD

Abstract: The color glass condensate approach describes successfully heavy ion collisions at RHIC. We investigate Iron-air collisions within this approach and compare results to event generators commonly used in air shower simulations. We estimate uncertainties in the extrapolation to GZK energies and discuss implications for air shower simulations.

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.