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

Understand

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.