Precise toppling balance, quenched disorder, and universality for sandpiles

A single sandpile model with quenched random toppling matrices captures the crucial features of different models of self-organized criticality. With symmetric matrices avalanche statistics falls in the multiscaling Bak-Tang-Wiesenfeld universality class. In the asymmetric case the simple scaling of the Manna model is observed. The presence or absence of a precise toppling balance between the amount of sand released by a toppling site and the total quantity the same site receives when all its neighbors topple once determines the appropriate universality class.     

Large Higgs mass and μ−e universality

In the limit of very large Higgs mass the Weinberg model becomes non-renormalizable, and this, in principle, provides for an upper limit on the Higgs mass. In actual fact, without further speculation, no useful limit emerges. Instead one is led to speculations on direct lepton hadron interactions violating μ?e universality. The experimental evidence on this point is considered.     

Diffusion in stochastic sandpiles

We study diffusion of particles in large-scale simulations of one-dimensional stochastic sandpiles, in both the restricted and unrestricted versions. The results indicate that the diffusion constant scales in the same manner as the activity density, so that it represents an alternative definition of an order parameter. The critical behavior of the unrestricted sandpile is very similar to that of its restricted counterpart, including the fact that a data collapse of the order parameter as a function of the particle density is possible, but with a narrow scaling region. We also develop a series expansion, in inverse powers of the density, for the collective diffusion coefficient in a variant of the stochastic sandpile in which the toppling rate at a site with n particles is n(n-1), and compare the theoretical prediction with simulation results.     

Large scale structure

We briefly discuss some aspects of the problem of forming large scale structures in the Universe. The basic picture that initially small perturbations generated by inflation grow by the process of gravitational instability to give the observed structures is largely consistent with the observations. The growth of the perturbations depends crucially on the contents of the Universe, and we discuss a few variants of the cold dark matter model. Many of these models are consistent with present observations. Future observations hold the possibility of deciding amongst these models.     

Confinement from spontaneous breaking of scale symmetry

We show that one can obtain naturally the confinement of static charges from the spontaneous symmetry breaking of scale invariance in a gauge theory. At the classical level a confining force is obtained and at the quantum level, using a gauge invariant but path-dependent variables formalism, the Cornell confining potential is explicitly obtained. Our procedure answers completely to the requirements by 't Hooft for “perturbative confinement”.     

Probing the universality of acceleration scale in modified Newtonian dynamics with SPARC galaxies

We probe the universality of acceleration scale a₀ in Milgrom's modified Newtonian dynamics(MOND)using the recently released rotation curve data from SPARC galaxies.We divide the SPARC data into different subsamples according to the morphological types of galaxies,and fit the rotation curve data of each subsample with the theoretical prediction of MOND.MOND involves an arbitrary interpolation function which connects the Newtonian region and the MOND region.Here we consider five different interpolation functions that are widely discussed in the literature.It is shown that the best-fitting a₀ significantly depends on the interpolation functions.For a specific interpolation function, a₀ also depends on the morphological types of galaxies,implying that a₀ may be not a universal constant.Introducing a dipole correction to a₀ can significantly improve the fits.The dipole directions for four of the five interpolation functions point towards an approximately consistent direction,but a₀ still varies for different interpolation functions.     

On the consistency of scale and chiral symmetry limits

We investigate theories in which the chiral and scale-invariant limits are realized in the Goldstone fashion with the appearance of an octet of pseudoscalar and one scalar, Goldstone bosons. A relation for the coupling constant is derived from the theory. The question of determining the dimension of the chiral symmetry breaking from both theoretical and phenomenological considerations is discussed.     

Y1(1385) production reactions,SU(3) symmetry and vector tensor universality

This paper is devoted to a detailed study of Y¹3(1385) production processes. It is shown that the present experimental data are consistent with SU(3) symmetry, broken by the Regge trajectory splitting. Furthermore an amplitude analysis is performed using the data on the $\text{K}{}^{\mathrm{?}}\text{p}\text{→ π}{}^{\mathrm{?}}\text{Y}{}^{\mathrm{1+}}$ reaction at incident momentum of 4.25 GeV/c. This determines the double-flip amplitude, the features of which are compatible with the systematics for vector and tensor exchanges proposed by the authors.     

Broken time-reversal symmetry in strongly correlated ladder structures

We provide, for the first time, in a doped strongly correlated system (two-leg ladder), a controlled theoretical demonstration of the existence of a state in which long-range ordered orbital currents are arranged in a staggered pattern, coexisting with a charge density wave. The method used is the highly accurate density-matrix renormalization group technique. This brings us closer to recent proposals that this order is realized in the enigmatic pseudogap phase of the cuprate high temperature superconductors.     

Kinematic segregation of granular mixtures in sandpiles

We study the segregation of granular mixtures in two-dimensional silos using a recently proposed set of coupled equations for surface flows of grains. We study the thick flow regime, where the grains are segregated in the rolling phase. We incorporate this dynamical segregation process, called kinematic sieving, free-surface segregation or percolation, into the theoretical formalism and calculate the profiles of the rolling species and the concentration of grains in the bulk in the steady state. Our solution shows the segregation of the mixture with the large grains being found at the bottom of the pile in qualitative agreement with experiments. Received: 6 July 1998 / Revised and Accepted: 13 August 1998     

Fields,particles and universality in two dimensions

We discuss the use of field theory for the exact determination of universal properties in two-dimensional statistical mechanics. After a compact derivation of critical exponents of main universality classes, we turn to the off-critical case, considering systems both on the whole plane and in presence of boundaries. The topics we discuss include magnetism, percolation, phase separation, interfaces, wetting.     

Invisible axion at an intermediate symmetry breaking scale

We suggest that qq?g mesons mat exist as low as 1 GeV in mass. The exotic J^PC=1^?+ multiplet will have distinctive decay modes and perhaps be relatively stable. The bag model spectrum of the lowest lying qq?g multiplet including hyperfine splittings is computed analogously to Jaffe's qq?qq? bag model multiplets. Relevance to light meson phenomenology is discussed.     

Large top-quark mass and nonlinear representation of flavor symmetry

We consider an effective theory (ET) approach to flavor-violating processes beyond the standard model, where the breaking of flavor symmetry is described by spurion fields whose low-energy vacuum expectation values are identified with the standard model Yukawa couplings. Insisting on canonical mass dimensions for the spurion fields, the large top-quark Yukawa coupling also implies a large expectation value for the associated spurion, which breaks part of the flavor symmetry already at the UV scale Lambda of the ET. Below that scale, flavor symmetry in the ET is represented in a nonlinear way by introducing Goldstone modes for the partly broken flavor symmetry and spurion fields transforming under the residual symmetry. As a result, the dominance of certain flavor structures in rare quark decays can be understood in terms of the 1/Lambda expansion in the ET.     

Internal structural symmetry of optimal layered structures

Problems of the optimal synthesis of multilayer structures implementing the ultimate performance under the action of elastic waves are considered. It is required to design a multilayered structure by choosing the physical properties of materials, the thickness of the layers, their number, and the mutual arrangement of layers with different physical properties in a way such that the energy characteristics of an elastic wave be as close as possible to the desired characteristics. From an analysis of the necessary optimum conditions, it is inferred that the optimal solutions are characterized by a certain internal order in the structure parameters, i.e., by an internal symmetry. When known a priori, these qualitative relations considerably reduce the number of variants tested for the optimum and make it possible to efficiently design composite structures implementing the ultimate performance in terms of exhibiting the desired properties under the action of elastic waves.     

Localization, Dirac fermions and Onsager universality

Disordered systems exhibiting exponential localization are mapped to anisotropic spin chains with localization length being related to the anisotropy of the spin model. This relates localization phenomenon in fermions to the rotational symmetry breaking in the critical spin chains. One of the intriguing consequence is that the statement of Onsager universality in spin chains implies universality of the localized fermions where the fluctuations in localized wave functions are universal. We further show that the fluctuations about localized nonrelativistic fermions describe relativistic fermions. This provides a new approach to understand the absence of localization in disordered Dirac fermions. We investigate how disorder affects well known universality of the spin chains by examining the multifractal exponents. Finally, we examine the effects of correlations on the localization characteristics of relativistic fermions. Received 28 September 2001 / Received in final form 30 November 2001 Published online 2 October 2002 RID="a" ID="a"e-mail: isatija@nickel.nist.gov     

Large scale spatio-temporal behaviour in surface growth

This paper presents new findings concerning the dynamics of the slow height variations in surfaces produced by the two-dimensional isotropic Kuramoto-Sivashinsky equation with an additional nonlinear term. In addition to the disordered cellular patterns of specific size evident at small scales, slow height variations of scale-free character become increasingly evident when the system size is increased. This paper focuses on the parameter range in which the kinetic roughening with eventual saturation in surface roughness and coarseness is obtained, and the statistical and dynamical properties of surfaces in the long-time stationary regime are investigated. The resulting long-range scaling properties of the saturated surface roughness consistent with the power-law shape of the surface spectrum at small wave numbers are obtained in a wider parameter range than previously reported. The temporal properties of these long-range height variations are investigated by analysing the time series of surface roughness fluctuations. The resulting power-spectral densities can be expressed as a generalized Lorentzian whose cut-off frequency varies with system size. The dependence of this lower cut-off frequency on the smallest wave number connects spatial and temporal properties and gives new insight into the surface evolution on large scales.