RP(n-1) model

The real-projective space (RP) model is given by

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where H is the Hamiltonian of the system, the variables $\sigma (x)$ are n-component unit vectors of sites x of a square lattice, and $\mu$ denotes the two directions of the lattice. The n=2 case of the model is equivalent to the XY model.

References

1. H. Kunz and G. Zumbach "Topological phase transition in a two-dimensional nematic n-vector model: A numerical study", Physical Review B 46 pp. 662 - 673 (1992)