# Causal dissipative hydrodynamics for QGP fluid in 2+1 dimensions

## TL;DR

This paper develops a 2+1 dimensional causal dissipative hydrodynamics model for quark-gluon plasma (QGP), revealing how viscosity affects the evolution, cooling, and elliptic flow of the fluid, with implications for understanding QGP behavior.

## Contribution

It introduces a causal viscous hydrodynamics framework for QGP in 2+1 dimensions, including the first study of quark elliptic flow saturation due to non-equilibrium effects.

## Key findings

- Viscous QGP cools slower than ideal fluid.
- Viscosity enhances transverse expansion.
- Quark elliptic flow saturates and cannot be replicated by ideal hydrodynamics.

## Abstract

In 2nd order causal dissipative theory, space-time evolution of QGP fluid is studied in 2+1 dimensions. Relaxation equations for shear stress tensors are solved simultaneously with the energy-momentum conservation equations. Comparison of evolution of ideal and viscous QGP fluid, initialized under the same conditions, e.g. same equilibration time, energy density and velocity profile, indicate that in a viscous dynamics, energy density or temperature of the fluid evolve slowly, than in an ideal fluid. Cooling gets slower as viscosity increases. Transverse expansion also increases in a viscous dynamics. For the first time we have also studied elliptic flow of 'quarks' in causal viscous dynamics. It is shown that elliptic flow of quarks saturates due to non-equilibrium correction to equilibrium distribution function, and can not be mimicked by an ideal hydrodynamics.