Holography and the speed of sound at high temperatures

TL;DR

This paper demonstrates that in a broad class of strongly interacting theories at high temperatures, the speed of sound universally approaches the conformal value from below, highlighting a fundamental aspect of holographic duality and scale anomalies.

Contribution

It establishes a universal behavior of the speed of sound in holographic theories at high temperatures, connecting it to the presence of a scalar field representing the scale anomaly.

Findings

Speed of sound approaches 1/3 from below at high temperatures.

Universality applies to theories with gravity duals coupled to a scalar field.

Highlights the role of scale anomaly in sound propagation.

Abstract

We show that in a general class of strongly interacting theories at high temperatures the speed of sound approaches the conformal value c_s^2=1/3 universally from_below_. This class includes theories holographically dual to a theory of gravity coupled to a single scalar field, representing the operator of the scale anomaly.