Causality violations in realistic simulations of heavy-ion collisions

Christopher Plumberg, Dekrayat Almaalol, Travis Dore, Jorge Noronha, Jacquelyn Noronha-Hostler

Published 2021-03-29Version 1

We show that causality is violated in the early stages of state-of-the-art heavy-ion hydrodynamic simulations. Up to $30\%$ of the initial fluid cells violate nonlinear causality constraints while the rest are uncertain. Only after 2-3 fm$/c$ of evolution do we find that $\sim 50\%$ of the fluid cells are definitely causal. Inclusion of pre-equilibrium evolution significantly reduces the number of acausal cells, but it does not eliminate them. Our findings suggest that relativistic causality places stringent constraints on the available model parameter space of heavy-ion collision simulations.