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arXiv 0709.0378cond-mat.stat-mechmath.PR
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螺旋模型:具有不连续玻璃化转变的元胞自动机

Spiral Model: a cellular automaton with a discontinuous glass transition

Cristina Toninelli, Giulio Biroli

摘要:

我们引入了一类新的二维元胞自动机,它具有自举类展开动力学。每个站点可以是空的或被单个粒子占据,并且动态遵循仅允许清空站点的离散时间的确定性更新规则。我们证明了阈值密度$ρ_c$收敛到一个完全空的配置是不平凡的,$0<ρ_c<1$,相反,标准的自举渗流。此外,我们证明,在亚临界制度,$ρ<ρ_c$,排空总是发生指数快速和$ρ_c$符合临界密度为二维定向网站渗流$\bZ^2$。这是已知的,也发生在一些元胞自动机与定向规则的过渡是连续的渐近密度值和交叉长度确定有限大小的影响发散作为一个幂律时,从下面接近临界密度。相反,对于我们的模型,我们证明了过渡是{ \it不连续},同时交叉长度发散{ \it比任何幂律更快}。的不连续性和下界的交叉长度的证明使用一个猜想的临界行为定向渗流。后者是支持几个数值模拟和分析(虽然不严格)的工作,通过重整化技术。最后,我们将讨论为什么,由于特殊的{ \it混合临界/一阶字符}的这种转变,该模型是特别相关的研究玻璃和干扰过渡。事实上,我们将表明,它导致一个动力学约束自旋模型的动态玻璃化转变。我们提出的大多数结果是与D. S. Fisher合作工作中提出的物理论点的严格证明。

英文摘要:

We introduce a new class of two-dimensional cellular automata with a bootstrap percolation-like dynamics. Each site can be either empty or occupied by a single particle and the dynamics follows a deterministic updating rule at discrete times which allows only emptying sites. We prove that the threshold density $ρ_c$ for convergence to a completely empty configuration is non trivial, $0<ρ_c<1$, contrary to standard bootstrap percolation. Furthermore we prove that in the subcritical regime, $ρ<ρ_c$, emptying always occurs exponentially fast and that $ρ_c$ coincides with the critical density for two-dimensional oriented site percolation on $\bZ^2$. This is known to occur also for some cellular automata with oriented rules for which the transition is continuous in the value of the asymptotic density and the crossover length determining finite size effects diverges as a power law when the critical density is approached from below. Instead for our model we prove that the transition is {\it discontinuous} and at the same time the crossover length diverges {\it faster than any power law}. The proofs of the discontinuity and the lower bound on the crossover length use a conjecture on the critical behaviour for oriented percolation. The latter is supported by several numerical simulations and by analytical (though non rigorous) works through renormalization techniques. Finally, we will discuss why, due to the peculiar {\it mixed critical/first order character} of this transition, the model is particularly relevant to study glassy and jamming transitions. Indeed, we will show that it leads to a dynamical glass transition for a Kinetically Constrained Spin Model. Most of the results that we present are the rigorous proofs of physical arguments developed in a joint work with D.S.Fisher.

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