Sébastien Ott
In this note we extend the analysis of a previous paper by the author to the Random Cluster model. The main result being that the pressure of the finite range ferromagnetic Ising model is analytic as a function of the inverse temperature in the regime $h=0$, $β>β_c$.
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Uniform analyticity of local observables in FK-percolation and analyticity of the Ising spontaneous magnetisation
论文证明了在FK渗流模型中，局部事件的概率在渗流参数p下均匀解析，并满足指数增长界，从而证明了Potts模型磁化率在合适参数范围内的解析性，包括伊辛模型在三维及以上所有超临界区域的解析性。
We prove that the pressure (or free energy) of the finite range ferromagnetic Ising model on $\mathbb{Z}^d$ is analytic as a function of both the inverse temperature $β$ and the magnetic field $h$ whenever the model has the exponential weak mixing property. We also prove the exponential weak mixing property whenever $h\neq 0$. Together with known results on the regime $h=0,β<β_c$, this implies both analyticity and weak mixing in all the domain of $(β,h)$ outside of the transition line $[β_c,\infty)\times \{0\}$. The proof of analyticity uses a graphical representation of the Glauber dynamic du…
We discuss the implications of studies of partition function zeros and equimodular curves for the analytic properties of the Ising model on a square lattice in a magnetic field. In particular we consider the dense set of singularities in the susceptibility of the Ising model at $H=0$ found by Nickel and its relation to the analyticity of the field theory computations of Fonseca and Zamolodchikov.
New results on the domain of analyticity of the free energy for the Ising model
本研究针对伊辛模型自由能解析性问题，结合多种数学方法推导改进收敛条件，基于维布伦定理的高温扩展得到了更大的解析区域。
We consider pairs of few-body Ising models where each spin enters a bounded number of interaction terms (bonds), such that each model can be obtained from the dual of the other after freezing $k$ spins on large-degree sites. Such a pair of Ising models can be interpreted as a two-chain complex with $k$ being the rank of the first homology group. Our focus is on the case where $k$ is extensive, that is, scales linearly with the number of bonds $n$. Flipping any of these additional spins introduces a homologically non-trivial defect (generalized domain wall). In the presence of bond disorder, we…
Analyticity, asymptotics and natural boundary for a one-point function of the finite-volume critical Ising chain
研究有限体积临界伊辛链中自旋算符的一点函数在不同基态间期望值的解析性、渐进行为及自然边界，揭示其与Lambert型级数的相似性及大N渐近行为。
Uniqueness, analyticity and mixing for Gibbs point processes via spectral gaps
本文通过定义势能的谱阈值，证明了吉布斯点过程在低于该阈值时的无限体积吉布斯测度唯一性、压力解析性以及时空混合性，显著改进了硬球模型的经典界，并给出了无相变势能的例子。
We prove an optimal $O(n \log n)$ mixing time of the Glauber dynamics for the Ising models with edge activity $β\in \left(\frac{Δ-2}Δ, \fracΔ{Δ-2}\right)$. This mixing time bound holds even if the maximum degree $Δ$ is unbounded. We refine the boosting technique developed in [CFYZ21], and prove a new boosting theorem by utilizing the entropic independence defined in [AJK+21]. The theorem relates the modified log-Sobolev (MLS) constant of the Glauber dynamics for a near-critical Ising model to that for an Ising model in a sub-critical regime.
We prove that Ising models on the hypercube with general quadratic interactions satisfy a Poincaré inequality with respect to the natural Dirichlet form corresponding to Glauber dynamics, as soon as the operator norm of the interaction matrix is smaller than $1$. The inequality implies a control on the mixing time of the Glauber dynamics. Our techniques rely on a localization procedure which establishes a structural result, stating that Ising measures may be decomposed into a mixture of measures with quadratic potentials of rank one, and provides a framework for proving concentration bounds fo…
We prove rapid mixing of the worm process for the zero-field ferromagnetic Ising model, on all finite connected graphs, and at all temperatures. As a corollary, we obtain a fully-polynomial randomized approximation scheme for the Ising susceptibility, and for a certain restriction of the two-point correlation function
We prove rapid mixing of the Prokofiev-Svistunov (or worm) algorithm for the zero-field ferromagnetic Ising model, on all finite graphs and at all temperatures. As a corollary, we show how to rigorously construct simple and efficient approximation schemes for the Ising susceptibility and two-point correlation function.
We considerably improve upon the recent result of Martinelli and Toninelli on the mixing time of Glauber dynamics for the 2D Ising model in a box of side $L$ at low temperature and with random boundary conditions whose distribution $P$ stochastically dominates the extremal plus phase. An important special case is when $P$ is concentrated on the homogeneous all-plus configuration, where the mixing time $T_{mix}$ is conjectured to be polynomial in $L$. In [MT] it was shown that for a large enough inverse-temperature $β$ and any $ε>0$ there exists $c=c(β,ε)$ such that $\lim_{L\to\infty}P(T_{mix}\…
In the heat-bath Glauber dynamics for the Ising model on the lattice, physicists believe that the spectral gap of the continuous-time chain exhibits the following behavior. For some critical inverse-temperature $β_c$, the inverse-gap is bounded for $β< β_c$, polynomial in the surface area for $β= β_c$ and exponential in it for $β> β_c$. This has been proved for $\Z^2$ except at criticality. So far, the only underlying geometry where the critical behavior has been confirmed is the complete graph. Recently, the dynamics for the Ising model on a regular tree, also known as the Bethe lattice, has …
We introduce a new framework for analyzing Glauber dynamics for the Ising model. The traditional approach for obtaining sharp mixing results has been to appeal to estimates on spatial properties of the stationary measure from within a multi-scale analysis of the dynamics. Here we propose to study these simultaneously by examining "information percolation" clusters in the space-time slab. Using this framework, we obtain new results for the Ising model on $(\mathbb{Z}/n\mathbb{Z})^d$ throughout the high temperature regime: total-variation mixing exhibits cutoff with an $O(1)$-window around the t…
We consider a two-dimensional Ising model with random i.i.d. nearest-neighbor ferromagnetic couplings and no external magnetic field. We show that, if the probability of supercritical couplings is small enough, the system admits a convergent cluster expansion with probability one. The associated polymers are defined on a sequence of increasing scales; in particular the convergence of the above expansion implies the infinite differentiability of the free energy but not its analyticity. The basic tools in the proof are a general theory of graded cluster expansions and a stochastic domination of …
Fast mixing in Ising models with a negative spectral outlier via Gaussian approximation
本文研究了存在单个负谱异常的Ising模型的Glauber动力学混合时间，通过高斯近似方法改进了传统方法，推导出改进的logarithmic Sobolev不等式和近最优混合时间界。
Boundary Free Energies, Quenched Mixing, and Gibbs-State Selection in Disordered Ising Models
该研究针对无序伊辛模型，证明了固定深度切向压力存在、吉布斯态选择独立性等结论，建立了全表面极限并给出反例，为相关统计物理问题提供了理论支撑。
Systematic scanning Glauber dynamics for the mean-field Ising model
研究完全图上系统扫描 Glauber 动力学的混合时间，证明高温区出现 cutoff，临界区混合时间为 n^{3/2}k^{-1}，低温区为 nk^{-1}log n。
Low-temperature Ising dynamics with random initializations
本文针对低温Ising模型Glauber动力学收敛慢的问题，提出基于“相内弱空间混合”的通用框架，证明了从随机混合初始化可显著加速收敛至Gibbs分布，并在多维环面和随机正则图上验证了其有效性。
Introduced in 1963, Glauber dynamics is one of the most practiced and extensively studied methods for sampling the Ising model on lattices. It is well known that at high temperatures, the time it takes this chain to mix in $L^1$ on a system of size $n$ is $O(\log n)$. Whether in this regime there is cutoff, i.e. a sharp transition in the $L^1$-convergence to equilibrium, is a fundamental open problem: If so, as conjectured by Peres, it would imply that mixing occurs abruptly at $(c+o(1))\log n$ for some fixed $c>0$, thus providing a rigorous stopping rule for this MCMC sampler. However, obtain…
The Supercritical Loop O(1) and Random Current models: Uniqueness and Mixing
本文研究超临界Ising模型在超立方晶格上的循环O(1)和随机电流模型，证明Gibbs测度的唯一性和指数比率弱混合性，采用Pisztora粗粒化方法的精细探索耦合技术。
We study Glauber dynamics for the Ising model on the complete graph on $n$ vertices, known as the Curie-Weiss Model. It is well known that at high temperature ($β< 1$) the mixing time is $Θ(n\log n)$, whereas at low temperature ($β> 1$) it is $\exp(Θ(n))$. Recently, Levin, Luczak and Peres considered a censored version of this dynamics, which is restricted to non-negative magnetization. They proved that for fixed $β> 1$, the mixing-time of this model is $Θ(n\log n)$, analogous to the high-temperature regime of the original dynamics. Furthermore, they showed \emph{cutoff} for the original dynam…
We give a survey of the known results on mixing time of Glauber dynamics for the Ising model on the square lattice and present a technique that makes exact sampling of the Ising model at all temperatures possible in polynomial time. At high temperatures this is well-known and although this seems to be known also in the low temperature case since Kramer and Waniers paper from the 1950s, we did not found any reference that describes exact sampling for the Ising model at low temperatures.
Fast relaxation of the random field Ising dynamics
研究了随机场Ising模型Glauber动力学的收敛性，在弱和强空间混合条件下分别证明了多项式和近多项式时间的混合，并构建了相应的近似采样算法。
Consider a low temperature stochastic Ising model in the phase coexistence regime with Markov semigroup $P_t$. A fundamental and still largely open problem is the understanding of the long time behavior of $\d_\h P_t$ when the initial configuration $\h$ is sampled from a highly disordered state $ν$ (e.g. a product Bernoulli measure or a high temperature Gibbs measure). Exploiting recent progresses in the analysis of the mixing time of Monte Carlo Markov chains for discrete spin models on a regular $b$-ary tree $\Tree^b$, we tackle the above problem for the Ising and hard core gas (independent …
The random-cluster model with parameters $(p,q)$ is a random graph model that generalizes bond percolation ($q=1$) and the Ising and Potts models ($q\geq 2$). We study its Glauber dynamics on $n\times n$ boxes $Λ_{n}$ of the integer lattice graph $\mathbb Z^2$, where the model exhibits a sharp phase transition at $p=p_c(q)$. Unlike traditional spin systems like the Ising and Potts models, the random-cluster model has non-local interactions. Long-range interactions can be imposed as external connections in the boundary of $Λ_n$, known as boundary conditions. For select boundary conditions that …
Noise sensitivity of crossings for high temperature Ising model
研究三角格点伊辛模型在亚临界温度下穿越事件的噪声敏感性，通过非谱方法分析初始与演化构型对的性质，证明该事件在Glauber动力学下是噪声敏感的。
We continue our study of exponential law for occurrences and returns of patterns in the context of Gibbsian random fields. For the low temperature plus phase of the Ising model, we prove exponential laws with error bounds for occurrence, return, waiting and matching times. Moreover we obtain a Poisson law for the number of occurrences of large cylindrical events and a Gumbel law for the maximal overlap between two independent copies. As a by-product, we derive precise fluctuation results for the logarithm of waiting and return times. The main technical tool we use, in order to control mixing, …
Free energy and quark potential in Ising lattice gauge theory via cluster expansion
本文利用簇展开方法研究低温下伊辛格点规范理论，证明自由能无限体积极限的存在性与解析性，并计算 Wilson 圈期望值的渐近展开，从而得到静态夸克势的展开式和强周长定律。
We study the Glauber dynamics for the zero-temperature Ising model in dimension d=4 with "plus" boundary condition.Let T+ be the time needed for an hypercube of size L entirely filled with "minus" spins to become entirely "plus". We prove that T+ is O(L^2(log L)^c) for some constant c, not depending on the dimension. This brings further rigorous justification for the so-called "Lifshitz law" T+ = O(L^2) [5, 3] conjectured on heuristic grounds. The key point of our proof is to use the detail knowledge that we have on the three-dimensional problem: results for fluctuation of monotone interfaces …
Supercritical sharpness for Ising double random currents
该研究证明了d≥3时伊辛双随机电流渗流模型的超临界尖锐性，简化了相关证明并得到伊辛模型截断关联指数衰减等应用结果。
We show that mixing for local, reversible dynamics of mean field spin glasses is exponentially slow in the low temperature regime. We introduce a notion of free energy barriers for the overlap, and prove that their existence imply that the spectral gap is exponentially small, and thus that mixing is exponentially slow. We then exhibit sufficient conditions on the equilibrium Gibbs measure which guarantee the existence of these barriers, using the notion of replicon eigenvalue and 2D Guerra Talagrand bounds. We show how these sufficient conditions cover large classes of Ising spin models for re…
Rapid phase ordering of Ising dynamics on $\mathbb Z^2$
研究低温度Ising动力学在偏向初始条件下的快速相序行为，证明在二维情况下存在阈值p₀，使得初始化为+1的概率p>p₀时，动力学快速收敛到+相位测度。
We prove comparison results for the Swendsen-Wang (SW) dynamics, the heat-bath (HB) dynamics for the Potts model and the single-bond (SB) dynamics for the random-cluster model on arbitrary graphs. In particular, we prove that rapid mixing of HB implies rapid mixing of SW on graphs with bounded maximum degree and that rapid mixing of SW and rapid mixing of SB are equivalent. Additionally, the spectral gap of SW and SB on planar graphs is bounded from above and from below by the spectral gap of these dynamics on the corresponding dual graph with suitably changed temperature. As a consequence we …
In this work we show that for every $d < \infty$ and the Ising model defined on $G(n,d/n)$, there exists a $β_d > 0$, such that for all $β< β_d$ with probability going to 1 as $n \to \infty$, the mixing time of the dynamics on $G(n,d/n)$ is polynomial in $n$. Our results are the first polynomial time mixing results proven for a natural model on $G(n,d/n)$ for $d > 1$ where the parameters of the model do not depend on $n$. They also provide a rare example where one can prove a polynomial time mixing of Gibbs sampler in a situation where the actual mixing time is slower than $n \polylog(n)$. Our…
The incipient infinite cluster of the FK-Ising model in dimensions $d\geq 3$ and the susceptibility of the high-dimensional Ising model
研究了FK-Ising模型在d≥3维度中的初始无限簇测度，并改进了高维Ising模型磁化率的渐进行为。
On any locally-finite geometry, the stochastic Ising model is known to be contractive when the inverse-temperature $β$ is small enough, via classical results of Dobrushin and of Holley in the 1970's. By a general principle proposed by Peres, the dynamics is then expected to exhibit cutoff. However, so far cutoff for the Ising model has been confirmed mainly for lattices, heavily relying on amenability and log Sobolev inequalities. Without these, cutoff was unknown at any fixed $β>0$, no matter how small, even in basic examples such as the Ising model on a binary tree or a random regular graph.…
We prove that the spectral gap of the Swendsen-Wang process for the Potts model on graphs with bounded degree is bounded from below by some constant times the spectral gap of any single-spin dynamics. This implies rapid mixing of the Swendsen-Wang process for the two-dimensional Potts model at all temperatures above the critical one, as well as rapid mixing at the critical temperature for the Ising model. After this we introduce a modified version of the Swendsen-Wang algorithm for planar graphs and prove rapid mixing for the two-dimensional Potts models at all non-critical temperatures.
We give the first comprehensive analysis of the effect of boundary conditions on the mixing time of the Glauber dynamics in the so-called Bethe approximation. Specifically, we show that spectral gap and the log-Sobolev constant of the Glauber dynamics for the Ising model on an n-vertex regular tree with plus-boundary are bounded below by a constant independent of n at all temperatures and all external fields. This implies that the mixing time is O(log n) (in contrast to the free boundary case, where it is not bounded by any fixed polynomial at low temperatures). In addition, our methods yield …
We study the Glauber dynamics for the random cluster (FK) model on the torus $(\mathbb{Z}/n\mathbb{Z})^2$ with parameters $(p,q)$, for $q \in (1,4]$ and $p$ the critical point $p_c$. The dynamics is believed to undergo a critical slowdown, with its continuous-time mixing time transitioning from $O(\log n)$ for $p\neq p_c$ to a power-law in $n$ at $p=p_c$. This was verified at $p\neq p_c$ by Blanca and Sinclair, whereas at the critical $p=p_c$, with the exception of the special integer points $q=2,3,4$ (where the model corresponds to the Ising/Potts models) the best-known upper bound on mixing …
In the study of Markov chain mixing times, analysis has centered on the performance from a worst-case starting state. Here, in the context of Glauber dynamics for the one-dimensional Ising model, we show how new ideas from information percolation can be used to establish mixing times from other starting states. At high temperatures we show that the alternating initial condition is asymptotically the fastest one, and, surprisingly, its mixing time is faster than at infinite temperature, accelerating as the inverse-temperature $β$ ranges from 0 to $β_0=\frac12\mathrm{arctanh}(\frac13)$. Moreover…
We introduce a notion called entropic independence that is an entropic analog of spectral notions of high-dimensional expansion. Informally, entropic independence of a background distribution $μ$ on $k$-sized subsets of a ground set of elements says that for any (possibly randomly chosen) set $S$, the relative entropy of a single element of $S$ drawn uniformly at random carries at most $O(1/k)$ fraction of the relative entropy of $S$. Entropic independence is the analog of the notion of spectral independence, if one replaces variance by entropy. We use entropic independence to derive tight mix…
We prove that the spectral gap of the Swendsen-Wang dynamics for the random-cluster model on arbitrary graphs with m edges is bounded above by 16 m log m times the spectral gap of the single-bond (or heat-bath) dynamics. This and the corresponding lower bound imply that rapid mixing of these two dynamics is equivalent. Using the known lower bound on the spectral gap of the Swendsen-Wang dynamics for the two dimensional square lattice $Z_L^2$ of side length L at high temperatures and a result for the single-bond dynamics on dual graphs, we obtain rapid mixing of both dynamics on $\Z_L^2$ at all…
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