TY - JOUR

T1 - Universal formula for the holographic speed of sound

AU - Anabalón, Andrés

AU - Andrade, Tomás

AU - Astefanesei, Dumitru

AU - Mann, Robert

N1 - Publisher Copyright:
© 2018 The Author(s)

PY - 2018/6/10

Y1 - 2018/6/10

N2 - We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner–Freedman window and derive a universal formula for the holographic speed of sound for any mixed boundary conditions of the scalar field. As an example, we numerically construct the most general class of planar black holes coupled to a single scalar field in the consistent truncation of type IIB supergravity that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. For this particular family of solutions, we find that the speed of sound exceeds the conformal value. From a phenomenological point of view, the fact that the conformal bound can be violated by choosing the right mixed boundary conditions is relevant for the existence of neutron stars with a certain mass-size relationship for which a large value of the speed of sound codifies a stiff equation of state. In the way, we also shed light on a puzzle regarding the appearance of the scalar charges in the first law. Finally, we generalize the formula of the speed of sound to arbitrary dimensional scalar-metric theories whose parameters lie within the Breitenlohner–Freedman window.

AB - We consider planar hairy black holes in five dimensions with a real scalar field in the Breitenlohner–Freedman window and derive a universal formula for the holographic speed of sound for any mixed boundary conditions of the scalar field. As an example, we numerically construct the most general class of planar black holes coupled to a single scalar field in the consistent truncation of type IIB supergravity that preserves the SO(3)×SO(3) R-symmetry group of the gauge theory. For this particular family of solutions, we find that the speed of sound exceeds the conformal value. From a phenomenological point of view, the fact that the conformal bound can be violated by choosing the right mixed boundary conditions is relevant for the existence of neutron stars with a certain mass-size relationship for which a large value of the speed of sound codifies a stiff equation of state. In the way, we also shed light on a puzzle regarding the appearance of the scalar charges in the first law. Finally, we generalize the formula of the speed of sound to arbitrary dimensional scalar-metric theories whose parameters lie within the Breitenlohner–Freedman window.

UR - http://www.scopus.com/inward/record.url?scp=85046376566&partnerID=8YFLogxK

U2 - 10.1016/j.physletb.2018.04.028

DO - 10.1016/j.physletb.2018.04.028

M3 - Article

AN - SCOPUS:85046376566

SN - 0370-2693

VL - 781

SP - 547

EP - 552

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

ER -