## Towards an understanding of thermalization in Heavy Ion Collision

### Thomas Epelbaum (Saclay)

1:30 PM, Tuesday, Sep. 18, NC State

Thermalization of the quark gluon plasma in heavy ion collisions is an
open problem that has given rise to many works in recent years.
On the one hand, viscous hydrodynamics simulations suggest that the
matter produced in such collisions (called the Quark Gluon Plasma, or
QGP) behaves like a nearly perfect fluid.
Since hydrodynamic models require local thermal equilibrium, this
tends to show that the QGP has thermalized very shortly after the
collision (around 1 fm/c).
On the other hand, theoretical models predict that the QGP is very far
from local thermal equilibrium at the initial time (its
energy-momentum is very anisotropic).

One of the approaches developed to study this non-perturbative problem
in QCD is a resummation
scheme that amounts to averaging over classical fields, with random
initial conditions. Its numerical implementation
is presented here for the case of a scalar field theory with quartic
coupling, that shares some important features with
QCD (scale invariance at the classical level and the presence of
instabilities). In particular, we will show the relevance
of this resummation in capturing the physics relevant for thermalization.