Random-cluster model on Z2 at the transition point
Random-cluster model on Z2 at the transition point
*note location*
The random-cluster model is defined on subgraphs of Z2 and has two parameters: cluster-weight q>0 and edge-probability 0<p<1. It is classical that, for each q≥1, the model undergoes a percolation phase transition when p=pc(q). Beffara and Duminil-Copin in 2010 computed pc(q), and later works established the type of the phase transition: it is continuous when 1≤q≤4 and discontinuous when q>4. The former is characterised by Russo-Seymour-Welsh estimates, while the latter asserts non-uniqueness of the infinite-volume DLR/Gibbs measure.
In this talk we revisit both parts of this diagram. When 1≤q≤4, we give a new proof of continuity that does not use parafermionic observable, nor Bethe Ansatz. When q>4, we establish invariance principle under Dobrushin boundary conditions: the interface converges to the Brownian bridge. Both arguments rely on the Baxter-Kelland-Wu correspondence that relates the random-cluster model to a certain height function (six-vertex model). Remarkably, we obtain also some result when q<1, though only at the self-dual point.