Kinetically constrained lattice gases: tagged particle diffusion

TL;DR

This paper proves that in kinetically constrained lattice gases, a tagged particle exhibits diffusive behavior converging to Brownian motion in all dimensions, challenging previous physics conjectures about phase transitions.

Contribution

It provides a rigorous proof of diffusive behavior for tagged particles in KCLG models across all dimensions, extending understanding of glassy dynamics.

Findings

Tracer converges to Brownian motion in all dimensions

No diffusive/non-diffusive transition occurs as previously conjectured

Technique applicable to other constraint models

Abstract

Kinetically constrained lattice gases (KCLG) are interacting particle systems on the integer lattice $\mathbb Z^d$ with hard core exclusion and Kawasaki type dynamics. Their peculiarity is that jumps are allowed only if the configuration satisfies a constraint which asks for enough empty sites in a certain local neighborhood. KCLG have been introduced and extensively studied in physics literature as models of glassy dynamics. We focus on the most studied class of KCLG, the Kob Andersen (KA) models. We analyze the behavior of a tracer (i.e. a tagged particle) at equilibrium. We prove that for all dimensions $d\geq 2$ and for any equilibrium particle density, under diffusive rescaling the motion of the tracer converges to a $d$-dimensional Brownian motion with non-degenerate diffusion matrix. Therefore we disprove the occurrence of a diffusive/non diffusive transition which had been conjectured in physics literature. Our technique is flexible enough and can be extended to analyse the tracer behavior for other choices of constraints.