Transient Casimir forces from quenches in thermal and active matter

TL;DR

This paper analyzes how sudden temperature changes induce transient Casimir forces in classical systems, revealing universal expressions and potential experimental realizations in active matter.

Contribution

It introduces a generic model showing transient Casimir forces after quenches, with universal force expressions and experimental proposals in active matter.

Findings

Transient forces appear even from force-free initial states.

Universal expressions for Casimir forces are derived.

Dynamical details only affect the time scaling of the force.

Abstract

We compute fluctuation-induced (Casimir) forces for classical systems after a temperature quench. Using a generic coarse-grained model for fluctuations of a conserved density, we find that transient forces arise even if the initial and final states are force-free. In setups reminiscent of Casimir (planar walls) and van der Waals (small inclusions) interactions, we find comparable exact universal expressions for the force. Dynamical details only scale the time axis of transient force curves. We propose that such quenches can be achieved, for instance, in experiments on active matter, employing tunable activity or interaction protocols.