A practical solution to the sign problem at finite theta-vacuum angle

TL;DR

This paper introduces a reweighting approach to mitigate the sign problem in lattice QCD simulations with a theta-vacuum term by minimizing the P-odd mass term, validated through NJL model estimates.

Contribution

It presents a practical reweighting method that reduces the sign problem in lattice QCD at finite theta, using a transformed Lagrangian and model-based reference system selection.

Findings

Effective reduction of the sign problem demonstrated.

Identification of a suitable reference system for reweighting.

Validation using the two-flavor NJL model.

Abstract

We propose a practical way of circumventing the sign problem in lattice QCD simulations with a theta-vacuum term. This method is the reweighting method for the QCD Lagrangian after the U_A(1) transformation. In the Lagrangian, the P-odd mass term as a cause of the sign problem is minimized. In order to find out a good reference system in the reweighting method, we estimate the average reweighting factor by using the two-flavor NJL model and eventually find a good reference system.