Phase diagram of the quantum O(2)-model in 2+1 dimensions

Abstract

The quantum O(2) model in 2+1 dimensions is studied by simulating the 3d O(2) model near criticality. Finite densities are introduced by a non-zero chemical potential mu, and the worm algorithm is used to circumvent the sign problem. The renormalisation is discussed in some detail. We find that the onset value of the chemical potential coincides with the mass gap. The mu-dependence of the density rules out Bose-Einstein condensation and might be compatible with an interacting Fermi gas. The mu-T phase diagram is explored using the density and the magnetic susceptibility. In the cold, but dense regime of the phase diagram, we find a superfluid phase.

broken references corrected

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• Baryonic Matter Onset in Two-Color QCD with Heavy Quarks
• Comparison of algorithms for solving the sign problem in the O(3) model in 1+1 dimensions at finite chemical potential
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• Berezinskii-Kosterlitz-Thouless-type transitions in d=2 quantum O(2) and O(2)xO(2) nonlinear sigma models
• Tensor-network study of the 3d $O(2)$ model at non-zero chemical potential and temperature