Model approach to the sign problem on lattice QCD with theta vacuum

TL;DR

This paper introduces a reweighting method to mitigate the sign problem in lattice QCD with a theta-vacuum term, and explores theta effects on the QCD phase diagram using effective models.

Contribution

It presents a practical reweighting approach to address the sign problem in lattice QCD with theta terms and analyzes theta effects on the phase diagram with extended PNJL models.

Findings

Theta-vacuum effects sharpen the chiral transition.

Transition temperature depends on theta and aligns with lattice results.

Method reduces sign problem in lattice QCD simulations with theta term.

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 chiral transformation. In the Lagrangian, the P-odd mass term as a cause of the sign problem is minimized. Additionally, we investigate theta-vacuum effects on the QCD phase diagram for the realistic 2+1 flavor system, using the three-flavor Polyakov-extended Nambu-Jona-Lasinio (PNJL) model and the entanglement PNJL model as an extension of the PNJL model. The theta-vacuum effects make the chiral transition sharper. We finally investigate theta dependence of the transition temperature and compare with the result of the pure gauge lattice simulation with imaginary theta parameter.