Critical behavior of lattice Schwinger model with topological term at $\theta=\pi$ using Grassmann tensor renormalization group

TL;DR

This study investigates the phase structure of the lattice Schwinger model with a topological term at = using Grassmann tensor renormalization group, revealing a first order transition and Ising universality class at the critical endpoint.

Contribution

The paper applies Grassmann tensor renormalization group to analyze the phase transition in the lattice Schwinger model with a  term at =, identifying the nature of the critical endpoint.

Findings

First order phase transition at larger fermion mass.

Critical endpoint belongs to Ising universality class.

Phase structure characterized by Lee-Yang and Fisher zero analyses.

Abstract

Lattice regularized Schwinger model with a so-called $\theta$ term is studied by using the Grassmann tensor renormalization group. We perform the Lee-Yang and Fisher zero analyses in order to investigate the phase structure at $\theta=\pi$. We find a first order phase transition at larger fermion mass. Both of the Lee-Yang zero and Fisher zero analyses indicate that the critical endpoint at which the first order phase transition terminates belongs to the Ising universality class.