Remarks on the multi-parameter reweighting method for the study of lattice QCD at non-zero temperature and density

TL;DR

This paper analyzes the effectiveness and limitations of the multi-parameter reweighting method in finite density lattice QCD, focusing on its applicability range, phase transition tracing, and the sign problem.

Contribution

It clarifies the parameter range where the reweighting method is effective and demonstrates its application to 2-flavor QCD through numerical simulations.

Findings

Reweighting fluctuations are minimized along the phase transition line.

The method is applicable over a wide parameter range for phase transition studies.

The sign problem due to complex phase fluctuations is analyzed.

Abstract

We comment on the reweighting method for the study of finite density lattice QCD. We discuss the applicable parameter range of the reweighting method for models which have more than one simulation parameter. The applicability range is determined by the fluctuations of the modification factor of the Boltzmann weight. In some models having a first order phase transition, the fluctuations are minimized along the phase transition line if we assume that the pressure in the hot and the cold phase is balanced at the first order phase transition point. This suggests that the reweighting method with two parameters is applicable in a wide range for the purpose of tracing out the phase transition line in the parameter space. To confirm the usefulness of the reweighting method for 2 flavor QCD, the fluctuations of the reweighting factor are measured by numerical simulations for the cases of reweighting in the quark mass and chemical potential directions. The relation with the phase transition line is discussed. Moreover, the sign problem caused by the complex phase fluctuations is studied.