Quantum fluctuations of energy in subsystems of a hot relativistic gas

TL;DR

This paper derives a formula for quantum energy fluctuations in subsystems of a hot relativistic gas, revealing size-dependent behavior and implications for heavy-ion collisions and other relativistic systems.

Contribution

It introduces a new formula for quantum energy fluctuations in relativistic gases, applicable across various fields dealing with hot, relativistic matter.

Findings

Small subsystems show increased fluctuations compared to thermodynamic predictions.

Large subsystems reproduce canonical ensemble fluctuations.

Implications for limitations of classical energy concepts in relativistic systems.

Abstract

We derive a formula that defines quantum fluctuations of energy in subsystems of a hot relativistic gas. For small subsystem sizes we find substantial increase of fluctuations compared to those known from standard thermodynamic considerations. However, if the size of the subsystem is sufficiently large, we reproduce the result for energy fluctuations in the canonical ensemble. Our results are subsequently used in the context of relativistic heavy-ion collisions to introduce limitations of the concepts such as classical energy density or fluid element. In the straightforward way, our formula can be applied in other fields of physics, wherever one deals with hot and relativistic matter.