Universal properties of 3d O(4) symmetric models: The scaling function of the free energy density and its derivatives

TL;DR

This paper provides explicit, numerically determined scaling functions of the 3d O(4) model's free energy density, facilitating comparisons with QCD and enabling analysis of universal properties of higher-order cumulants.

Contribution

It introduces direct, overlapping expansions of the scaling functions around z=0 and at infinity, derived from high-statistics lattice data, for the first time.

Findings

Explicit expansion coefficients for the scaling functions.

Smooth representations of derivatives of the free energy density.

Universal properties of higher-order cumulants in QCD.

Abstract

We present direct representations of the scaling functions of the 3d O(4) model which are relevant for comparisons to other models, in particular QCD. This is done in terms of expansions in the scaling variable z=t/h^{1/\beta\delta}. The expansions around z=0 and the corresponding asymptotic ones for z --> +/- infty, overlap such that no interpolation is needed. We explicitly present the expansion coefficients which have been determined numerically from data of a previous high statistics simulation of the O(4) model on a three-dimensional lattice of linear extension L=120. This allows to derive smooth representations of the first three derivatives of the scaling function of the free energy density, which determine universal properties of up to sixth order cumulants of net charge fluctuations in QCD.