Indications of a non-trivial vacuum in the effective theory of perfect fluids

TL;DR

This paper explores the vacuum structure of a field theory modeling perfect fluids, using lattice techniques, and finds suggestive but inconclusive evidence of a non-trivial, possibly turbulent vacuum state that challenges the effectiveness of gradient expansion.

Contribution

It provides the first lattice-based investigation into the vacuum structure of perfect fluid field theories, revealing potential non-trivial vacua that impact effective field theory approaches.

Findings

Evidence suggests a non-trivial vacuum state with turbulent characteristics.

The vacuum may carry entropy through macroscopic degrees of freedom.

Results cast doubt on the adequacy of gradient expansion for these systems.

Abstract

Using lattice field theory techniques, we investigate the vacuum structure of the field theory corresponding to perfect fluid dynamics in the Lagrangian prescription. We find intriguing, but inconclusive evidence, that the vacuum of such a theory is non-trivial, casting doubts on whether the gradient expansion can provide a good effective field theory for this type of system. The non-trivial vacuum looks like a "turbulent" state where some of the entropy is carried by macroscopic degrees of freedom. We describe further steps to strengthen or falsify this evidence.