Critical point particle number fluctuations from molecular dynamics

TL;DR

This study uses molecular dynamics simulations of Lennard-Jones fluids to investigate how particle number fluctuations signal the presence of a critical point, revealing that measurement conditions significantly affect observed fluctuations.

Contribution

It provides a detailed dynamical analysis of critical point fluctuations using molecular dynamics, highlighting the impact of measurement methods on fluctuation signals.

Findings

Large fluctuations appear in coordinate space near the critical point.

Momentum cuts diminish the observable fluctuations.

Results inform interpretation of event-by-event fluctuations in heavy-ion collisions.

Abstract

We study fluctuations of particle number in the presence of critical point by utilizing molecular dynamics simulations of the classical Lennard-Jones fluid in a periodic box. The numerical solution of the $N$-body problem naturally incorporates all correlations, exact conservation laws, and finite size effects, allowing us to study the fluctuation signatures of the critical point in a dynamical setup. We find that large fluctuations associated with the critical point are observed when measurements are performed in coordinate subspace, but, in the absence of collective flow and expansion, are essentially washed out when momentum cuts are imposed instead. We put our findings in the context of event-by-event fluctuations in heavy-ion collisions.