Phase diagram of the 4D U(1) model at finite temperature

TL;DR

This paper investigates the phase diagram of the 4D compact U(1) gauge theory at finite temperature, revealing a change from first to second order phase transition as temperature increases, with a tricritical point identified.

Contribution

It provides the first detailed analysis of the finite-temperature phase transitions in the 4D U(1) model, identifying the tricritical point and clarifying previous conflicting results.

Findings

First order transition at zero temperature becomes second order at high temperature.

A tricritical point exists between L_t=5 and 6.

Reconciliation of previous contradictory evidence in the literature.

Abstract

We explore the phase diagram of the 4D compact U(1) gauge theory at finite temperature as a function of the gauge coupling and of the compactified Euclidean time dimension L_t. We show that the strong-to-weak coupling transition, which is first order at T=0 (L_t=\infty), becomes second order for high temperatures, i.e. for small values of L_t, with a tricritical temporal size \bar{L_t} located between 5 and 6. The critical behavior around the tricritical point explains and reconciles previous contradictory evidences found in the literature.