Some numerical results on the block spin transformation for the 2D Ising model at the critical point

We study the block spin transformation for the 2D Ising model at the critical temperatureT _c . We consider the model with the constraint that the total spin in each block is zero. An old argument by Cassandro and Gallavotti strongly supports the Gibbsianness of the transformed measure, provided that such model has a critical temperatureT _c lower thanT _c . After describing a possible rigorous approach to the problem, we present numerical evidence that indeedT _c <T _c and study the Dobrushin-Shlosman uniqueness condition.     

Renormalization-Group Transformations Under Strong Mixing Conditions: Gibbsianness and Convergence of Renormalized Interactions

In this paper we study a renormalization-group map: the block averaging transformation applied to Gibbs measures relative to a class of finite-range lattice gases, when suitable strong mixing conditions are satisfied. Using a block decimation procedure, cluster expansion, and detailed comparison between statistical ensembles, we are able to prove Gibbsianness and convergence to a trivial (i.e., Gaussian and product) fixed point. Our results apply to the 2D standard Ising model at any temperature above the critical one and arbitrary magnetic field.     

A renormalization group explanation of numerical observations of analyticity domains

A recent paper considers the dependence of the size of analyticity domains of some functions appearing in KAM theory as a function of the distance to breakdown. They tentatively conclude that the relation is linear. In this note we argue that McKay's renormalization group picture predicts a power-law dependence with an exponent close to 1 but not equal to 1.     

The roughening transition of the three-dimensional Ising interface: A Monte Carlo study

We study the roughening transition of an interface in an Ising system on a 3D simple cubic lattice using a finite-size scaling method. The particular method has recently been proposed and successfully tested for various solid-on-solid models. The basic idea is the matching of the renormalization-groupflow of the interface with that of the exactly solvable body-centered cubic solid-on-solid model. We unambiguously confirm the Kosterlitz-Thouless nature of the roughening transition of the Ising interface. Our result for the inverse transition temperatureK _r=0.40754(5) is almost two orders of magnitude more accurate than the estimate of Mon, Landau, and Stauffer.     

Renormalization group for Markov chains and application to metastability

In this paper we introduce a new renormalization group method for the study of the long-time behavior of Markov chains with finite state space and with transition probabilities exponentially small in an external parameter. A general approach of metastability problems emerges from this analysis and is discussed in detail in the case of a two-dimensional Ising system at low temperature,     

A Renormalization Group Study of the Ising Model on a Triangular Lattice with Long-Range Interactions

The critical exponents of the triangular lattice Ising model with long-range interactions γ^-s are calculated by the real space renormalization group. Using the simplest Kadanoff blocks and the lowest approximation of cumulant expansion, it is shown that there exists a finite critical temperature when 4(1 - ㏑2/㏑3) < s < 4.     

采用正方元胞的Ising模型实空间重正化群解

在二维正方形晶格上,将元胞取为4格点正方形,采用3种不同的规则定义块自旋状态,进行了重正化群计算,得出了更为精确的结果;解决了元胞内格点数为偶数的重正化群计算问题.     

Renormalization group study of a three-dimensional lattice model with directional bonding

We consider a bcc lattice model in which each site is either vacant or occupied by a molecule. The molecules have four symmetrically arranged arms directed towards four of the eight nearest-neighbor sites. Two molecules form a bond if they have bonding arms pointing towards each other and along their line of centers. We introduce bonding energies as well as two-, three-, and four-molecule interactions. The model is studied using a real-space renormalization group method. The form of the pressure-temperature phase diagram is found to be very sensitive to small changes in the relative sizes of the energy parameters. Adjustment of these parameters allows us to obtain a phase diagram which resembles that of the ice-water-steam system. The nature of the transitions between the various ordered phases is examined and the critical exponents are obtained.     

Stability of interfaces in a random environment. A rigorous renormalization group analysis of a hierarchical model

We study a hierarchical model of domain walls in aD-dimensional bond disordered Ising model at low temperatures. Using a renormalization group method inspired by the work of Bricmont and Kupiainen for the random field Ising model, we prove the existence of rigid interfaces at low enough temperatures in dimensionsD>3.     

Pathological behavior of renormalization-group maps at high fields and above the transition temeprature

We show that decimation transformations applied to high-q Potts models result in non-Gibbsian measures even for temperatures higher than the transition temperature. We also show that majority transformations applied to the Ising model in a very strong field at low temperatures produce non-Gibbsian measures. This shows that pathological behavior of renormalization-group transformations is even more widespread than previous examples already suggested.     

Renormalization Conditions and the Sliding Scale in the Implicit Regularization Scheme: A Simple Connection

We describe in detail how a sliding scale is introduced in the renormalization of a QFT according to integer-dimensional implicit regularization scheme. We show that since no regulator needs to be specified at intermediate steps of the calculation, the introduction of a mass scale is a direct consequence of a set of renormalization conditions. As an illustration the one-loop -function for QED and ⁴ theories are derived. They are given in terms of derivatives of appropriately systematized functions (related to definite parts of the amplitudes) with respect to a mass scale . Our formal scheme can be easily generalized for higher loop calculations.     

Memory,Time and Technique Aspects of Density Matrix Renormalization Group Method

We present the memory size,computational time,and technique aspects of density matrix renormalization group (DMRG) algorithm.We show how to estimate the memory size and computational time before starting a large scale DMRG calculation.We propose an implementation of the Hamiltonian wavefunction multiplication and a wavefunction initialization in DMRG with block matrix data structure.One-dimensional Heisenberg model is used to illustrate our study.``     

Renormalization group and analyticity in one dimension: A proof of Dobrushin's theorem

We consider one dimensional systems described by many body potentials with finite first moment and prove that the correlation functions are analytic in the interaction parameters. This result is not new (Dobrushin, 1973) but our proof is simpler and physically more transparent. We show that by introducing suitable blocks and averaging over the variables associated to a subset of the blocks (decimation procedure), the resulting effective interaction is such that the system can always be dealt with as a high temperature system.     

The Renormalization Group and Optimization of Entropy

We illustrate the possible connection that exists between the extremal properties of entropy expressions and the renormalization group (RG) approach when applied to systems with scaling symmetry. We consider three examples: (1) Gaussian fixed-point criticality in a fluid or in the capillary-wave model of an interface; (2) Lévy-like random walks with self-similar cluster formation; and (3) long-ranged bond percolation. In all cases we find a decreasing entropy function that becomes minimum under an appropriate constraint at the fixed point. We use an equivalence between random-walk distributions and order-parameter pair correlations in a simple fluid or magnet to study how the dimensional anomaly at criticality relates to walks with long-tailed distributions.     

Memory,Time and Technique Aspects of Density Matrix Renormalization Group Method

We present the memory size,computational time,and technique aspects of density matrix renormalization group (DMRG) algorithm.We show how to estimate the memory size and computational time before starting a large scale DMRG calculation.We propose an implementation of the Hamiltonian wavefunction multiplication and a wavefunction initialization in DMRG with block matrix data structure.One-dimensional Heisenberg model is used to illustrate our study.     

Universality and Conformal Invariance for the Ising Model in Domains with Boundary

The partition function with boundary conditions for various two-dimensional Ising models is examined and previously unobserved properties of nonformal invariance and universality are established numerically.     

The density of states in the Anderson model at weak disorder: A renormalization group analysis of the hierarchical model

We study the density of states in a hierarchical approximation of the Anderson tight-binding model at weak disorder using a renormalization group approach. Since the Laplacian term in our model is hierarchical, the renormalization group transformations act essentially on the local potential distribution and the energy. Technically, we use the supersymmetric replica trick and study the averaged Green's function. Starting with a Gaussian distribution with small variance, we find that the density of states is analytic as soon as the variance of the potential is turned on, except possibly near the band edge, where we can show this only for>2, which corresponds tod>4. Moreover, it is perturbatively close to the free one, except near the eigenvalues of the (hierarchical) Laplacian, where it is given (up to perturbative corrections) by the rescaled potential distribution.     

Scaling,Renormalization and Statistical Conservation Laws in the Kraichnan Model of Turbulent Advection

We present a systematic way to compute the scaling exponents of the structure functions of the Kraichnan model of turbulent advection in a series of powers of ξ, adimensional coupling constant measuring the degree of roughness of the advecting velocity field. We also investigate the relation between standard and renormalization group improved perturbation theory. The aim is to shed light on the relation between renormalization group methods and the statistical conservation laws of the Kraichnan model, also known as zero modes.     

Renormalization group study of Mullins' equation for molecular beam epitaxy with conserved noise

The dynamics of driven interfaces under conserved noise in a continuum model of growth by a molecular beam has been studied by means of the Noziéres-Gallet dynamic renormalization group technique, using the results of Sun and Plischke for the case of non-conserved noise. Relaxation of the growing film is due to both surface tension and surface diffusion. In (1 + 1) dimensions, four growth regimes have been found. None of these are purely diffusive. One of these fixed points has negative surface tension and is stable with respect to renormalization group flow. This is an unstable growth state in which the creation of large slopes in the interface configuration is expected. In (2 + 1) dimensions, seven growth regimes have been found, in which three are purely diffusive. There is also one fixed point with a negative surface tension. However, this fixed point is unstable with respect to renormalization group flow, and is therefore expected to crossover into the other growth regimes at large system size and long times.     

Critical Exponents of the Diluted Ising Model between Dimensions 2 and 4

Within the massive field-theoretic renormalization-group approach the expressions for the and functions of the anisotropic mn-vector model are obtained for general space dimension d in three-loop approximation. Resumming corresponding asymptotic series, critical exponents for the case of the weakly diluted quenched Ising model (m = 1, n = 0), as well as estimates for the marginal order parameter component number m _c of the weakly diluted quenched m-vector model, are calculated as functions of d in the region 2 d < 4. Conclusions concerning the effectiveness of different resummation techniques are drawn.