Effective Field Theory of ideal-fluid Hydrodynamics

TL;DR

This paper develops an effective field theory for ideal-fluid hydrodynamics, explaining sound modes as Goldstone bosons from Galilei invariance breaking, and clarifies differences from superfluid behavior.

Contribution

It derives a Galilei-invariant effective theory for ideal fluids, linking sound modes to spontaneous symmetry breaking, and clarifies distinctions from superfluid dynamics.

Findings

Sound mode is a Goldstone boson of Galilei invariance breaking

The theory reproduces all hydrodynamic equations for ideal fluids

Differences between ideal fluid and superfluid are highlighted

Abstract

Starting from a standard description of an ideal, isentropic fluid, we derive the effective theory governing a gapless non-relativistic mode---the sound mode. The theory, which is dictated by the requirement of Galilei invariance, entails the entire set of hydrodynamic equations. The gaplessness of the sound mode is explained by identifying it as the Goldstone mode associated with the spontaneous breakdown of Galilei invariance. Differences with a superfluid are pointed out.