Volume dependence of baryon number cumulants and their ratios

TL;DR

This paper investigates how finite volume effects influence baryon number fluctuations using a non-perturbative chiral model and the functional renormalization group, highlighting regulator choices and the behavior of apparent critical points.

Contribution

It demonstrates the impact of finite volume on baryon number cumulants and compares smooth versus sharp regulators, revealing spurious artifacts and the movement of apparent critical points.

Findings

Sharp regulator produces spurious artifacts in finite volume.

Finite volume creates apparent critical points with shifted locations.

Small volumes lead to multiple apparent critical points.

Abstract

We explore the influence of finite volume effects on baryon number fluctuations in a non-perturbative chiral model. In order to account for soft modes, we use the functional renormalization group in a finite volume, using a smooth regulator function in momentum space. We compare the results for a smooth regulator with those for a sharp (or Litim) regulator, and show that in a finite volume, the latter produces spurious artifacts. In a finite volume there are only apparent critical points, about which we compute the ratio of the fourth to the second order cumulant of quark number fluctuations. When the volume is sufficiently small the system has two apparent critical points; as the system size decreases, the location of the apparent critical point can move to higher temperature and lower chemical potential.