Phase transition for the Glauber dynamics for the independent sets on regular trees

We study the effect of boundary conditions on the relaxation time of the Glauber dynamics for the hard-core model on the tree. The hard-core model is defined on the set of independent sets weighted by a parameter λ, called the activity. The Glauber dynamics is the Markov chain that updates a randomly chosen vertex in each step. On the infinite tree with branching factor b, the hard-core model can be equivalently defined as a broadcasting process with a parameter ω which is the positive solution to λ=ω(1+ω)b, and vertices are occupied with probability ω/(1+ω) when their parent is unoccupied. This broadcasting process undergoes a phase transition between the so-called reconstruction and non-reconstruction regions at ωr≈ln b/b. Reconstruction has been of considerable interest recently since it appears to be intimately connected to the efficiency of local algorithms on locally tree-like graphs, such as sparse random graphs. In this paper we show that the relaxation time of the Glauber dynamics on regular b-ary trees Th of height h and n vertices, undergoes a phase transition around the reconstruction threshold. In particular, we construct a boundary condition for which the relaxation time slows down at the reconstruction threshold. More precisely, for any ω≤ln b/b, for Th with any boundary condition, the relaxation time is Ω(n) and O(n1+ob(1)). In contrast, above the reconstruction threshold we show that for every δ>0, for ω=(1+δ)ln b/b, the relaxation time on Th with any boundary condition is O(n1+δ+ob(1)), and we construct a boundary condition where the relaxation time is Ω(n1+δ/2−ob(1))