Factorised stationary states for a long range misanthrope process

The misanthrope process is an interacting particle system where particles move between neighbouring sites with hop rates depending only on the number of particles at the departure and arrival sites. Motivated by a discretised version of the Hammersley–Aldous–Diaconis process, we introduce a partially asymmetric long range misanthrope process (PALRMP) on a finite one-dimensional lattice with periodic boundary conditions where particles can move between sites that are not necessarily neighbours, as long as there are no particles in between the departure and arrival sites. In this model, each site $\ell$ has an inhomogeneous rate parameter $x_\ell$ associated to it, and the hop rate of a particle moving from site $k$ to site $\ell$ depends upon the parameter associated to the target site $x_\ell$, the direction the particle moves, and the number of particles at sites $k$ and $\ell$. We also consider the homogeneous PALRMP, where all the $x_\ell$’s are 1. We find necessary and sufficient conditions on the hop rates under which the stationary distribution is of factorised form for both the PALRMP and the homogeneous PALRMP, as well as the extreme variants, namely the ones where the particle motion is totally asymmetric (TALRMP) and symmetric (SLRMP). As an illustrative example, we study in detail the discrete Hammersley–Aldous–Diaconis process.

💡 Research Summary

The paper introduces a new class of interacting particle systems called the Partially Asymmetric Long‑Range Misanthrope Process (PALRMP). In the classic misanthrope process, particles hop only between neighboring sites with rates that depend on the occupancies of the departure and arrival sites. PALRMP generalises this by allowing a particle to jump over arbitrarily many empty sites: a move from site k to site ℓ is permitted provided every site strictly between k and ℓ is empty. Each site ℓ carries a positive “rate parameter” xℓ; the hop rate from k (with m particles) to ℓ (with n particles) is xℓ · u(m,n) when the particle moves clockwise, and q · xℓ · u(m,n) when it moves counter‑clockwise, where q≥0 measures the degree of asymmetry and u(m,n) is a base rate function.

The authors first establish that, under the empty‑interval condition, the state space is irreducible for any positive u and xℓ, guaranteeing a unique stationary distribution. They then focus on the central question: when does this stationary distribution factorise, i.e. can be written as a product over sites, \