Statistical mechanics of a cold tracer in a hot bath

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Hauptverfasser: Al-Hiyasat, Amer, Ro, Sunghan, Tailleur, Julien
Format: Preprint
Veröffentlicht: 2025
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author Al-Hiyasat, Amer
Ro, Sunghan
Tailleur, Julien
author_facet Al-Hiyasat, Amer
Ro, Sunghan
Tailleur, Julien
contents We study the dynamics of a zero-temperature particle interacting linearly with a bath of hot Brownian particles. Starting with the most general model of a linearly-coupled bath, we eliminate the bath degrees of freedom exactly to map the tracer dynamics onto a generalized Langevin equation, allowing for an arbitrary external potential on the tracer. We apply this result to determine the fate of a tracer connected by springs to $N$ identical bath particles or inserted within a harmonic chain of hot particles. In the former "fully-connected" case, we find the tracer to transition between an effective equilibrium regime at large $N$ and an FDT-violating regime at finite $N$, while in the latter "loop" model the tracer never satisfies an FDT. We then study the fully-connected model perturbatively for large but finite $N$, demonstrating signatures of irreversibility such as ratchet currents, non-Boltzmann statistics, and positive entropy production. Finally, we specialize to harmonic external potentials on the tracer, allowing us to exactly solve the dynamics of both the tracer and the bath for an arbitrary linear model. We apply our findings to show that a cold tracer in a hot lattice suppresses the fluctuations of the lattice in a long-ranged manner, and we generalize this result to linear elastic field theories.
format Preprint
id arxiv_https___arxiv_org_abs_2503_01998
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Statistical mechanics of a cold tracer in a hot bath
Al-Hiyasat, Amer
Ro, Sunghan
Tailleur, Julien
Statistical Mechanics
Soft Condensed Matter
We study the dynamics of a zero-temperature particle interacting linearly with a bath of hot Brownian particles. Starting with the most general model of a linearly-coupled bath, we eliminate the bath degrees of freedom exactly to map the tracer dynamics onto a generalized Langevin equation, allowing for an arbitrary external potential on the tracer. We apply this result to determine the fate of a tracer connected by springs to $N$ identical bath particles or inserted within a harmonic chain of hot particles. In the former "fully-connected" case, we find the tracer to transition between an effective equilibrium regime at large $N$ and an FDT-violating regime at finite $N$, while in the latter "loop" model the tracer never satisfies an FDT. We then study the fully-connected model perturbatively for large but finite $N$, demonstrating signatures of irreversibility such as ratchet currents, non-Boltzmann statistics, and positive entropy production. Finally, we specialize to harmonic external potentials on the tracer, allowing us to exactly solve the dynamics of both the tracer and the bath for an arbitrary linear model. We apply our findings to show that a cold tracer in a hot lattice suppresses the fluctuations of the lattice in a long-ranged manner, and we generalize this result to linear elastic field theories.
title Statistical mechanics of a cold tracer in a hot bath
topic Statistical Mechanics
Soft Condensed Matter
url https://arxiv.org/abs/2503.01998