ENTROPY CREATION IN RELATIVISTIC HEAVY ION COLLISIONS

We review current ideas on entropy production during the different stages of a relativistic nuclear collision. This includes recent results on decoherence entropy and the entropy produced during the hydrodynamic phase by viscous effects. We start by a discussion of decoherence caused by gluon bremsstrahlung in the very first interactions of gluons from the colliding nuclei. We then present a general framework, based on the Husimi distribution function, for the calculation of entropy growth in quantum field theories, which is applicable to the early ("glasma") phase of the collision during which most of the entropy is generated. The entropy calculated from the Husimi distribution exhibits linear growth when the quantum field contains unstable modes and the growth rate is asymptotically equal to the Kolmogorov–Sinaï entropy. We outline how the approach can be used to investigate the problem of entropy production in a relativistic heavy ion reaction from first principles. We show that the same result can be obtained in the framework of a completely different approach called eigenstate thermalization hypothesis. Finally we discuss some recent results on entropy production in the strong coupling limit, as obtained from AdS/CFT duality.

PARALLEL IMPLEMENTATION OF 3 + 1-DIMENSIONAL RELATIVISTIC HYDRODYNAMICS

We discuss the parallel implementation of 3 + 1-dimensional relativistic hydrodynamics. The discretization of these equations is performed with a basis-spline collocation method. An iterative procedure for the time evolution will also be discussed. Approximately 60% of the computational effort is spent in performing vector-matrix multiplications that may easily be vectorized. Furthermore, for large lattices, these operations may be spread across the nodes of a parallel machine. We show how to accomplish this partitioning for the hydrodynamic evolution equations. A double-ring, message-passing algorithm is shown to enhance overall code performance when compared to a single ring on iPSC/i860 architectures. Overall code performance is discussed, and an application to relativistic nuclear collision physics is presented.

DISORIENTED CHIRAL CONDENSATE IN (1+1) LORENTZ-INVARIANT GEOMETRY

We consider isospin correlations of pions produced in a relativistic nuclear collision, using an effective theory of the chiral order parameter. Our theory has (1+1) Lorentz invariance as appropriate for the central rapidity region. We argue that in certain regions of space correlations of the chiral order parameter are described by the fixed point of the (1+1) WZNW model. The corresponding anomalous dimension determines scaling of the probability to observe a correlated cluster of pions with the size of this cluster in rapidity. Though the maximal size of clusters for which this scaling is applicable is cutoff by pion mass, such clusters can still include sufficiently many particles to make the scaling observable.