Tricriticality in 4D U(1) Lattice Gauge Theory

TL;DR

This study uses advanced Monte Carlo simulations to explore the phase diagram of 4D U(1) lattice gauge theory, revealing unexpected tricritical points and a possible continuous transition at zero temperature, challenging previous beliefs.

Contribution

The paper identifies a second tricritical point and suggests a continuous phase transition at zero temperature, providing new insights into the phase structure of 4D U(1) gauge theory.

Findings

Identification of a tricritical point at T/K_0 ≈ 0.19

Critical exponents match 3D O(2) model at high T

Evidence of a second tricritical point near T/K_0 ≈ 0.05

Abstract

The 4D compact U(1) gauge theory has a well-established phase transition between a confining and a Coulomb phase. In this paper, we revisit this model using state-of-the-art Monte Carlo simulations on anisotropic lattices. We map out the coupling-temperature phase diagram, and determine the location of the tricritical point, $T/K_0 \simeq 0.19$, below which the first-order transition is observed. We find the critical exponents of the high-temperature second-order transition to be compatible with those of the 3-dimensional $O(2)$ model. Our results at higher temperatures can be compared with literature results and are consistent with them. Surprisingly, below $T/K_0 \simeq 0.05$ we find strong indications of a second tricritical point where the first-order transition becomes continuous. These results suggest an unexpected second-order phase transition extending down to zero temperature, contrary to the prevailing consensus. If confirmed, these findings reopen the question of the detailed characterization of the transition including a suitable field theory description.