# QCD thermodynamics in the crossover/freeze-out region

## TL;DR

This paper uses high-order Taylor expansions of the QCD equation of state to analyze conserved charge fluctuations, revealing limitations of the hadron resonance gas model near the crossover temperature.

## Contribution

It introduces a sixth-order Taylor expansion approach to study QCD thermodynamics and challenges the validity of the hadron resonance gas model in the crossover region.

## Key findings

- Cumulants of conserved charges strongly limit hadron resonance gas model applicability.
- Hadron resonance gas model is inadequate at T~155 MeV for equilibrium QCD properties.
- High-order Taylor expansions provide precise constraints on QCD thermodynamics.

## Abstract

We use results from a 6-th order Taylor expansion of the QCD equation of state to construct expansions for cumulants of conserved charge fluctuations and their correlations. We show that these cumulants strongly constrain the range of applicability of hadron resonance gas model calculations. We point out that the latter is inappropriate to describe equilibrium properties of QCD at zero and non-zero values of the baryon chemical potential already at T~155 MeV.