The "ripples" on relativistically expanding fluid

TL;DR

This paper derives analytical sound wave solutions on relativistically expanding backgrounds, enhancing understanding of fluctuations in heavy ion collision fireballs and their impact on experimental observables.

Contribution

It provides complete analytic solutions for sound waves on Bjorken and Hubble flow backgrounds, advancing the theoretical modeling of fluctuations in relativistic hydrodynamics.

Findings

Analytic solutions for sound waves on Bjorken flow

Analytic solutions for sound waves on Hubble flow

Implications for fluctuation analysis in heavy ion collisions

Abstract

Recent studies have shown that fluctuations of various types play important roles in the evolution of the fireball created in relativistic heavy ion collisions and bear many phenomenological consequences for experimental observables. The bulk dynamics of the fireball is well described by relativistic hydrodynamic expansion and the fluctuations on top of such expanding background can be studied within the linearized hydrodynamic framework. In this work we present complete and analytic sound wave solutions on top of both Bjorken flow and Hubble flow backgrounds. We also briefly discuss the applications of these solutions in heavy ion collisions.