This repository contains the equation of state (EoS) of the hadron resonance gas consisting of the degrees of freedom of the SMASH transport approach. It can for example be employed in hydrodynamics+transport hybrid approaches to match the equation of state at the transition hypersurface.
When using the SMASH HRG EoS presented herein, please cite
A. Schäfer, I. Karpenko, H. Elfner: "Conservation laws in a novel hybrid approach".
The SMASH HRG EoS is provided in tabulated format mapping from the energy density e, baryon density nB and electric charge density nQ to the temperature T, pressure p, baryon chemical potential μB, charge chemical potential μQ and strangeness chemical potential μS: (e, nB, nQ) -> (T, p, μB, μQ, μS)
It is determined from the partition function of an ideal Boltzmann gas consisting of the SMASH degrees of freedom, assuming a grand-canonical ensemble and resonances at their pole masses.
The table containing the SMASH HRG EoS (hadgas_eos_SMASH.dat) consists of 8 columns with explicitly these quantities in order: [e nB nQ T p μB μS μQ]
The units are GeV/fm3 for the energy density and pressure, 1/fm3 for the baryon and charge density, and GeV for the temperature and the chemical potentials. The EoS presented herein covers the range e ∈ [0.01, 1.0] GeV/fm3, nB ∈ [0.0, 0.5] GeV/fm3, and nQ ∈ [-0.1, 0.4] GeV/fm3. It is perfectly accurate at higher energy densities, but constitutes an approximation at lower energy densities. The reason is that the root solver algorithm employed to determine the equation of state is highly-sensitive to the choice of the initial approximation and has convergence issues at low energy densities as well as close to the kinematic thresholds. As such the resulting equation of state at low energy densities is approximated by combining the results of different initial approximations, interpolations, and extrapolations of the solver results in the unproblematic regions. For further details, please consult A. Schäfer, I. Karpenko, H. Elfner: arXiv:2109.08578.