Sound Waves in (2+1) Dimensional Holographic Magnetic Fluids

TL;DR

This paper investigates sound wave propagation in strongly coupled (2+1)D conformal magnetic fluids using AdS/CFT, confirming some hydrodynamic predictions and revealing the need for higher-order corrections.

Contribution

It provides a dual gravity and field theory analysis of sound attenuation and speed modification in magnetic fluids, highlighting discrepancies at higher orders.

Findings

Magnetic field can attenuate sound or reduce its speed.

Leading order dispersion matches between gravity and field theory.

Discrepancy at higher order indicates need for extended hydrodynamics.

Abstract

We use the AdS/CFT correspondence to study propagation of sound waves in strongly coupled (2+1) dimensional conformal magnetic fluids. Our computation provides a nontrivial consistency check of the viscous magneto-hydrodynamics of Hartnoll-Kovtun-Muller-Sachdev to leading order in the external field. Depending on the behavior of the magnetic field in the hydrodynamic limit, we show that it can lead to further attenuation of sound waves in the (2+1) dimensional conformal plasma, or reduce the speed of sound. We present both field theory and dual supergravity descriptions of these phenomena. While to the leading order in momenta the dispersion of the sound waves obtained from the dual supergravity description agrees with the one predicted from field theory, we find a discrepancy at higher order. This suggests that further corrections to HKMS magneto-hydrodynamics are necessary.