Effective shear viscosity from the friction term in relativistic multi-fluid hydrodynamics
Abstract
Within a three-fluid description of heavy-ion collisions, we investigate how nuclear friction can be used to model shear stress. In this multi-fluid approach, the individual fluids (projectile, target and fireball) are each treated as locally equilibrated ideal fluids at all times, while the local energy-momentum tensor of the superposed system exhibits characteristic anisotropies in its Landau rest frame. From the corresponding non-vanishing shear stress densities and the gradients of the Landau velocity field, we infer an ``effective shear viscosity'' according to the Navier-Stokes relation. We present the time evolution of the resulting values of ηeff and the generated entropy density in nuclear collisions at different beam energies (1.23 AGeV ≤ Elab ≤ 29.7 AGeV). The resulting dimensionless ratio ηeff/s is determined dynamically and self-consistently within the non-equilibrium friction model. We discuss the relation to previous calculations using alternative methods in hydrodynamics and to estimates based on microscopic transport models.
Related
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BibTeX
@misc{spieles2026effective,
title = {{Effective shear viscosity from the friction term in relativistic multi-fluid hydrodynamics}},
author = {Christian Spieles and Marcus Bleicher},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.20872},
eprint = {2610.20872},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.20872},
}
RIS
TY - UNPB
TI - Effective shear viscosity from the friction term in relativistic multi-fluid hydrodynamics
AU - Christian Spieles
AU - Marcus Bleicher
PY - 2026
DA - 2026/10/14
PB - arXiv
DO - 10.48550/arxiv.2610.20872
UR - https://arxiv.org/abs/2610.20872
AB - Within a three-fluid description of heavy-ion collisions, we investigate how nuclear friction can be used to model shear stress. In this multi-fluid approach, the individual fluids (projectile, target and fireball) are each treated as locally equilibrated ideal fluids at all times, while the local energy-momentum tensor of the superposed system exhibits characteristic anisotropies in its Landau rest frame. From the corresponding non-vanishing shear stress densities and the gradients of the Landau velocity field, we infer an ``effective shear viscosity'' according to the Navier-Stokes relation. We present the time evolution of the resulting values of η_eff and the generated entropy density in nuclear collisions at different beam energies (1.23 AGeV ≤ E_lab ≤ 29.7 AGeV). The resulting dimensionless ratio η_eff/s is determined dynamically and self-consistently within the non-equilibrium friction model. We discuss the relation to previous calculations using alternative methods in hydrodynamics and to estimates based on microscopic transport models.
ER -