Robust phase transitions for Heisenberg and other models on general trees

• 成果类型: Article
• 署名作者: Pemantle, R; Steif, JE
• 署名单位: University of Wisconsin System; University of Wisconsin Madison; Chalmers University of Technology
• 刊物名称: ANNALS OF PROBABILITY
• ISSN/ISSBN: 0091-1798
• DOI: 10.1214/aop/1022677389
• 发表日期: 1999
• 页码: 876-912
• 关键词: contact process; random-walks; percolation; graphs

摘要

We study several statistical mechanical models on a general tree. Particular attention is devoted to the classical Heisenberg models, where the state space is the d-dimensional unit sphere and the interactions are proportional to the cosines of the angles between neighboring spins. The phenomenon of interest here is the classification of phase transition (nonuniqueness of the Gibbs state) according to whether it is robust. in many cases, including all of the Heisenberg and Potts models, occurrence of robust phase transition is determined by the geometry (branching number) of the tree in a way that parallels the situation with independent percolation and usual phase transition for the Ising model. The critical values for robust phase transition for the Heisenberg and Potts models are also calculated exactly. In some cases, such as the q greater than or equal to 3 Potts model, robust phase transition and usual phase transition do not coincide, while in other cases, such as the Heisenberg models, we conjecture that robust phase transition and usual phase transition are equivalent. In addition, we show that symmetry breaking is equivalent to the existence of a phase transition, a fact believed but not known for the rotor model on Z(2).