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Updated: Apr 17, 2026

Ultrasound Velocity Measurement in a Liquid Metal Electrode
Published on: August 5, 2015
Sound velocity bound and neutron stars
Paulo Bedaque1, Andrew W Steiner2
1Department of Physics, University of Maryland, College Park, Maryland 20742, USA.
Abstract:
It has been conjectured that the velocity of sound in any medium is smaller than the velocity of light in vacuum divided by sqrt[3]. Simple arguments support this bound in nonrelativistic and/or weakly coupled theories. The bound has been demonstrated in several classes of strongly coupled theories with gravity duals and is saturated only in conformal theories. We point out that the existence of neutron stars with masses around two solar masses combined with the knowledge of the equation of state of hadronic matter at "low" densities is in strong tension with this bound.
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