119852951
On the link between strong and weak coupling expansions for the SU(2) lattice gauge theory
The intermediate region between the strong and weak coupling expansions of SU(2) lattice gauge theory is analyzed by inverting the strong coupling series of the average plaquette energy Ep(J). 
 
Taking into account the weak coupling behaviour too, we get Pade approximants for J(Ep) valid in the whole physical region. The zeros of pJ/pEp are mapped into singularities of Ep(J); they occur for complex values of J and give rise to a peak in the specific heat in fair agreement with the Monte Carlo simulation data. The variable Ep is further used to analyze the strong coupling expansions for the roughening indicator, the string tension and the mass gap.
122714395
Passive-Scalar Fluctuations in Intermittent Turbulence
We discuss how the spatial intermittency of energy dissipation in 3D fully developed turbulence affects the small-scale statistics of passive scalars. We relate the passive-scalar behaviour to the diffusion properties of particle pairs in turbulent fluids. We thus find the intermittency correction to the -5/3 Obukhov-Corrsin law for the power spectrum of a passive scalar at wavenumber k where molecular diffusion and viscosity play a negligible role (inertial convective subrange). This correction is positive at difference with the negative correction to the -5/3 Kolmogorov law for the energy spectrum. We finally show that the structure functions of passive scalars have scaling exponents linear in the moment order, even in the framework of multifractal models.
123292838
The non-linear sigma model: 3-loop renormalization and lattice scaling
Abstract We present a perturbative calculation of the first non-universal terms of the renormalization group functions for the non-linear σ-model regularized on a lattice, for a choice of different lattice actions. Such terms, hitherto unknown, fix the leading corrections to universal asymptotic scaling. However, by comparing with Monte Carlo simulations, one sees that the actual deviations from universal scaling are due to non-perturbative effects, and not to perturbative analytic corrections. The latter are nonetheless relevant to determine the ratios of scaling operators to Λ-parameters.
123085141
Intermittency and Multifractality in Magnetic Dynamos
We study the convection of magnetic fields in the presence of Lagrangian chaos, i.e. when nearby fluid elements diverge exponentially in time. We show that the magnetic field is of a multifractal nature as a consequence of the spatial fluctuations in the exponential growth of the field. We provide numerical and theoretical evidence that the magnetic fields can concentrate in small domains of a fluid with weak Lagrangian chaos. Moreover, these properties are relevant also for the study of the case of small but nonzero magnetic diffusivity.
120014368
A new proposal for the determination of the renormalization group trajectories by the Monte Carlo renormalization group method
Abstract We present a new method for calculating block renormalized couplings by Monte Carlo renormalization group. This method has several advantages with respect to the existing ones and can be applied for any value of the coupling constants. A preliminary numerical study of the 2-dimensional O(3) non linear σ-model is also presented.
123419934
Complex singularities in the specific heat of the SU(2) lattice gauge model
Abstract A recent Monte Carlo simulation showing a sharp peak versus β in the specific heat for an SU(2) lattice gauge theory is compared with the high temperature expansion. An interpretation based on complex β -plane singularities is proposed.
8220387
Phantom Tubules
We provide the first numerical evidence for the existence of the tubule phase, predicted by Radzihovsky and Toner (RT), for anisotropic tethered membranes. Incorporating anisotropy into the bending rigidity of a simple model of a phantom tethered membrane with the topology of a disk and free boundary conditions we show that the model indeed has two phase transitions corresponding to the flat-to-tubule and tubule-to-crumpled transitions. For the tubule phase we measure the Flory exponent νF , describing the growth of the tubule radius with the extent of the tubule, and the roughness exponent ζ, which measures the r.m.s. height fluctuations in the extended direction. We find νF = 0.305(14) and ζ = 0.895(60) which are in reasonable agreement with the theoretical predictions of RT, νF = 1/4 and ζ = 1. PACS numbers: 64.60.Fr, 05.40.+j, 82.65.Dp Typeset using REVTEX