Identify the origin of out-of-bounds fluid cells relative to the lattice QCD equation of state

Ascertain whether the failure to find consistent thermodynamic combinations of energy density and BSQ charge densities {ε, ρ_B, ρ_S, ρ_Q} in the lattice-QCD-based 4D equation of state at low energy densities arises from limitations of the Taylor-series lattice QCD equation of state or from a breakdown of the perturbative quark–antiquark pair production assumption in the ICCING initial condition generator; determine the conditions under which each cause dominates to guide improvements to the equation of state and initial-state modeling.

Background

When coupling the ICCING initial conditions (which model gluon splittings into quark–antiquark pairs) to hydrodynamics using a 4D lattice-QCD-based equation of state, the authors encounter fluid cells for which no solution can be found in the EoS table at low energy densities. They note this may be due to the limited validity of the Taylor-series expansion of the EoS at large densities or to a breakdown of the perturbative assumptions underlying quark–antiquark production.

The authors explicitly state that it is currently not possible to determine which of these factors is responsible without access to a more reliable EoS in the large-density regime, motivating an investigation of the failure modes and their separation.