16,905 research outputs found
Non-diffusive transport in plasma turbulence: a fractional diffusion approach
Numerical evidence of non-diffusive transport in three-dimensional, resistive
pressure-gradient-driven plasma turbulence is presented. It is shown that the
probability density function (pdf) of test particles' radial displacements is
strongly non-Gaussian and exhibits algebraic decaying tails. To model these
results we propose a macroscopic transport model for the pdf based on the use
of fractional derivatives in space and time, that incorporate in a unified way
space-time non-locality (non-Fickian transport), non-Gaussianity, and
non-diffusive scaling. The fractional diffusion model reproduces the shape, and
space-time scaling of the non-Gaussian pdf of turbulent transport calculations.
The model also reproduces the observed super-diffusive scaling
Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics
We explore the existence of time reparametrization symmetry in p-spin models.
Using the Martin-Siggia-Rose generating functional, we analytically probe the
long-time dynamics. We perform a renormalization group analysis where we
systematically integrate over short timescale fluctuations. We find three
families of stable fixed points and study the symmetry of those fixed points
with respect to time reparametrizations. One of those families is composed
entirely of symmetric fixed points, which are associated with the low
temperature dynamics. The other two families are composed entirely of
non-symmetric fixed points. One of these two non-symmetric families corresponds
to the high temperature dynamics.
Time reparametrization symmetry is a continuous symmetry that is
spontaneously broken in the glass state and we argue that this gives rise to
the presence of Goldstone modes. We expect the Goldstone modes to determine the
properties of fluctuations in the glass state, in particular predicting the
presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature
(non-symmetric) and low temperature (symmetric) renormalization group fixed
points. Now 16 pages with 1 figure. v1: 13 page
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