Extend tensor renormalization methods to generalized XY models with p ≥ 3 fractional-vortex interactions

Develop and apply higher-order tensor renormalization group (HOTRG) techniques, as used for the q=2 generalized XY model on the square lattice, to generalized XY models whose Hamiltonians include interactions of the form cos(p(θ_i − θ_j)) for integers p ≥ 3 that support fractional vortices.

Background

This work analyzes the two-dimensional generalized XY (gXY) model with q=2 using higher-order tensor renormalization group (HOTRG) methods, mapping out Berezinskii-Kosterlitz-Thouless (BKT), half-BKT, and Ising transition lines and their meeting region in the T−Δ plane.

The authors note that for models with interactions cos(p(θ_i − θ_j)) with p ≥ 3, Monte Carlo studies suggest richer phase structures. However, a corresponding tensor-network treatment has not yet been carried out, motivating the open problem of extending and applying HOTRG to these fractional-vortex models.