• Accepted Paper

Hierarchical Lorentz mirror model: Normal transport and a universal 2/3 mean-variance law

Raphaël Lefevere and Hal Tasaki

Phys. Rev. Lett. - Accepted 27 October, 2026

DOI: https://doi.org/10.1103/mrqx-4nlv

Abstract

The Lorentz mirror model provides a clean setting to study macroscopic transport generated solely by quenched environmental randomness. We introduce a hierarchical version whose distribution of left–right crossings satisfies an exact recursion. In dimensions d≥3, we prove two-sided bounds that support normal transport: the mean conductance scales as (cross-section)/(length). A Gaussian closure, supported by numerics, predicts that the variance-to-mean ratio of the dimensionless conductance converges to the universal value 2/3 for all d≥2 (the ``2/3 law’’). We provide numerical evidence for the 2/3 law in the original (non-hierarchical) Lorentz mirror model in d=3, and conjecture that it is a universal signature of normal transport induced by random current matching. In the marginal case d=2, our hierarchical recursion reproduces the known scaling of the mean and variance of conductance.

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