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 -