QCD Equation of State and Hadron Resonance Gas

TL;DR

This paper compares lattice QCD results with the hadron resonance gas model, identifies discrepancies, and proposes a combined parametrization of the QCD equation of state for use in hydrodynamic simulations.

Contribution

It introduces a modified hadron resonance gas model accounting for lattice quark masses and lattice spacing, and provides a unified QCD equation of state parametrization.

Findings

Discrepancies between HRG and lattice data are significant.

Modifying the HRG spectrum reduces discrepancies.

The proposed parametrization aligns well with lattice results and impacts hydrodynamic modeling.

Abstract

We compare the trace anomaly, strangeness and baryon number fluctuations calculated in lattice QCD with expectations based on hadron resonance gas model. We find that there is a significant discrepancy between the hadron resonance gas and the lattice data. This discrepancy is largely reduced if the hadron spectrum is modified to take into account the larger values of the quark mass used in lattice calculations as well as the finite lattice spacing errors. We also give a simple parametrization of QCD equation of state, which combines hadron resonance gas at low temperatures with lattice QCD at high temperatures. We compare this parametrization with other parametrizations of the equation of state used in hydrodynamical models and discuss differences in hydrodynamic flow for different equations of state.