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arXiv · 2311.12147

On anomalous diffusion in the Kraichnan model and correlated-in-time variants

Keefer Rowan
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Abstract

We provide a concise PDE-based proof of anomalous diffusion in the Kraichan model -- a stochastic, white-in-time model of passive scalar turbulence. That is, we show an exponential rate of $L^2$ decay in expectation of a passive scalar advected by a certain white-in-time, correlated-in-space, divergence-free Gaussian field, uniform in the initial data and the diffusivity of the passive scalar. Additionally, we provide examples of correlated-in-time versions of the Kraichnan model which fail to exhibit anomalous diffusion despite their (formal) white-in-time limits exhibiting anomalous diffusion. As part of this analysis, we prove that anomalous diffusion of a scalar advected by some flow implies non-uniqueness of the ODE trajectories of that flow.

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Keefer Rowan. 2023-11-20. On anomalous diffusion in the Kraichnan model and correlated-in-time variants. https://arxiv.org/abs/2311.12147

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