One-dimensional q-state Potts model with multi-site interactions

A one-dimensional (1D) $q$-state Potts model with $N$ sites, $m$-site interaction $K$ in a field $H$ is studied for arbitrary values of $m$. Exact results for the partition function and the two-point correlation function are obtained at $H=0$. The system in a field is shown to be self-dual. Using a change of Potts variables, it is mapped onto a standard 2D Potts model, with first-neighbour interactions $K$ and $H$, on a cylinder with helical boundary conditions (BC). The 2D system has a length $N\mathrm{/}m$ and a transverse size $m$. Thus the Potts chain with multi-site interactions is expected to develop a 2D critical singularity along the self-duality line, $(e^{qK}-1)(e^{qH}-1)=q$, when $N\mathrm{/}m\to \mathrm{\infty }$ and $m\to \mathrm{\infty }$.