Acausality-driven instabilities in transient relativistic viscous hydrodynamics

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Main Authors: Gavassino, Lorenzo, Hirvonen, Henry, Paquet, Jean-François, Singh, Mayank, Rocha, Gabriel Soares
Format: Preprint
Published: 2025
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author Gavassino, Lorenzo
Hirvonen, Henry
Paquet, Jean-François
Singh, Mayank
Rocha, Gabriel Soares
author_facet Gavassino, Lorenzo
Hirvonen, Henry
Paquet, Jean-François
Singh, Mayank
Rocha, Gabriel Soares
contents We investigate non-linear instabilities stemming from superluminal propagation of information in Israel-Stewart-like models of relativistic viscous fluid dynamics. In relativity, the characteristic speed of propagation of information, $w$, and the speed of the fluid, $v$, allow us to differentiate between regimes of the hydrodynamic equations that are acausal but stable ($w>1$), unstable ($v^{2} w^{2} \geq 1$), and covariantly ill-posed ($w^{2} \leq 0$). As an analytical benchmark, we present a new solution that illustrates these distinct regimes. We compare this analytical solution to the result of a numerical relativistic viscous fluid dynamics solver, and confirm that the analytical result can be recovered numerically in the stable regime, whether causal or acausal. The onset of numerical instabilities is further found to occur in the regime predicted by the analytical solution.
format Preprint
id arxiv_https___arxiv_org_abs_2508_04918
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Acausality-driven instabilities in transient relativistic viscous hydrodynamics
Gavassino, Lorenzo
Hirvonen, Henry
Paquet, Jean-François
Singh, Mayank
Rocha, Gabriel Soares
Nuclear Theory
High Energy Physics - Phenomenology
We investigate non-linear instabilities stemming from superluminal propagation of information in Israel-Stewart-like models of relativistic viscous fluid dynamics. In relativity, the characteristic speed of propagation of information, $w$, and the speed of the fluid, $v$, allow us to differentiate between regimes of the hydrodynamic equations that are acausal but stable ($w>1$), unstable ($v^{2} w^{2} \geq 1$), and covariantly ill-posed ($w^{2} \leq 0$). As an analytical benchmark, we present a new solution that illustrates these distinct regimes. We compare this analytical solution to the result of a numerical relativistic viscous fluid dynamics solver, and confirm that the analytical result can be recovered numerically in the stable regime, whether causal or acausal. The onset of numerical instabilities is further found to occur in the regime predicted by the analytical solution.
title Acausality-driven instabilities in transient relativistic viscous hydrodynamics
topic Nuclear Theory
High Energy Physics - Phenomenology
url https://arxiv.org/abs/2508.04918