56 research outputs found
Phase transitions in general gravity theories
Phase transitions between two competing vacua of a given theory are quite
common in physics. We discuss how to construct the space-time solutions that
allow the description of phase transitions between different branches (or
asymptotics) of a given higher curvature gravity theory at finite temperature.Comment: 4 pages, 1 figure, Contribution to the Conference Proceedings of the
Spanish Relativity Meeting in Portugal (ERE2012
A Lovelock black hole bestiary
We revisit the study of (A)dS black holes in Lovelock theories. We present a
new tool that allows to attack this problem in full generality. In analyzing
maximally symmetric Lovelock black holes with non-planar horizon topologies
many distinctive and interesting features are observed. Among them, the
existence of maximally symmetric vacua do not supporting black holes in vast
regions of the space of gravitational couplings, multi-horizon black holes, and
branches of solutions that suggest the existence of a rich diagram of phase
transitions. The appearance of naked singularities seems unavoidable in some
cases, raising the question about the fate of the cosmic censorship conjecture
in these theories. There is a preferred branch of solutions for planar black
holes, as well as non-planar black holes with high enough mass or temperature.
Our study clarifies the role of all branches of solutions, including
asymptotically dS black holes, and whether they should be considered when
studying these theories in the context of AdS/CFT.Comment: 40 pages, 16 figures; v2: references added and minor amendments; v3:
title changed to improve its accuracy and general reorganization of the
results to ameliorate their presentatio
Classical instability in Lovelock gravity
We introduce a simple method for the investigation of the classical stability
of static solutions with a horizon in Lovelock gravity. The method is
applicable to the investigation of high angular momentum instabilities, similar
to those found by Dotti and Gleiser for Gauss-Bonnet black holes. The method
does not require the knowledge of the explicit analytic form of the black hole
solution. In this paper we apply our method to a case where the explicit
solution is known and show that it identifies correctly the resulting unstable
modes.Comment: 13 pages, 2 figure
The Shear Viscosity to Entropy Ratio: A Status Report
This review highlights some of the lessons that the holographic gauge/gravity
duality has taught us regarding the behavior of the shear viscosity to entropy
density in strongly coupled field theories. The viscosity to entropy ratio has
been shown to take on a very simple universal value in all gauge theories with
an Einstein gravity dual. Here we describe the origin of this universal ratio,
and focus on how it is modified by generic higher derivative corrections
corresponding to curvature corrections on the gravity side of the duality. In
particular, certain curvature corrections are known to push the viscosity to
entropy ratio below its universal value. This disproves a longstanding
conjecture that such a universal value represents a strict lower bound for any
fluid in nature. We discuss the main developments that have led to insight into
the violation of this bound, and consider whether the consistency of the theory
is responsible for setting a fundamental lower bound on the viscosity to
entropy ratio.Comment: 29 pages. Invited review for Modern Physics Letters B. References and
minor comments adde
Effectively four-dimensional spacetimes emerging from d=5 Einstein-Gauss-Bonnet Gravity
Einstein-Gauss-Bonnet gravity in five-dimensional spacetime provides an
excellent example of a theory that, while including higher-order curvature
corrections to General Relativity, still shares many of its features, such as
second-order field equations for the metric. We focus on the largely unexplored
case where the coupling constants of the theory are such that no
constant-curvature solution is allowed, leaving open the question of what the
vacuum state should then be. We find that even a slight deviation from the
anti-de Sitter Chern-Simons theory, where the vacuum state is five-dimensional
AdS spacetime, leads to a complete symmetry breakdown, with the fifth dimension
either being compactified into a small circle or shrinking away exponentially
with time. A complete family of solutions, including duality relations among
them, is uncovered and shown to be unique within a certain class. This
dynamical dimensional reduction scenario seems particularly attractive as a
means for higher-dimensional theories to make contact with our four-dimensional
world.Comment: 9 pages, 4 figures. v2: New section on geometrical significance of
solutions. Final version for CQ
Causality in AdS/CFT and Lovelock theory
We explore the constraints imposed on higher curvature corrections of the
Lovelock type due to causality restrictions in the boundary of asymptotically
AdS space-time. In the framework of AdS/CFT, this is related to positivity of
the energy constraints that arise in conformal collider physics. We present
explicit analytic results that fully address these issues for cubic Lovelock
gravity in arbitrary dimensions and give the formal analytic results that
comprehend general Lovelock theory. The computations can be performed in two
ways, both by considering a thermal setup in a black hole background and by
studying the scattering of gravitons with a shock wave in AdS. We show that
both computations coincide in Lovelock theory. The different helicities, as
expected, provide the boundaries defining the region of allowed couplings. We
generalize these results to arbitrary higher dimensions and discuss their
consequences on the shear viscosity to energy density ratio of CFT plasmas, the
possible existence of Boulware-Deser instabilities in Lovelock theory and the
extent to which the AdS/CFT correspondence might be valid for arbitrary
dimensions.Comment: 35 pages, 20 figures; v2: minor amendments and clarifications
include
Conformal field theories and deep inelastic scattering
Theoretical Physic
Holographic studies of quasi-topological gravity
Quasi-topological gravity is a new gravitational theory including
curvature-cubed interactions and for which exact black hole solutions were
constructed. In a holographic framework, classical quasi-topological gravity
can be thought to be dual to the large limit of some non-supersymmetric
but conformal gauge theory. We establish various elements of the AdS/CFT
dictionary for this duality. This allows us to infer physical constraints on
the couplings in the gravitational theory. Further we use holography to
investigate hydrodynamic aspects of the dual gauge theory. In particular, we
find that the minimum value of the shear-viscosity-to-entropy-density ratio for
this model is .Comment: 45 pages, 6 figures. v2: References adde
Causality constraints in AdS/CFT from conformal collider physics and Gauss-Bonnet gravity
We explore the relation between positivity of the energy constraints in
conformal field theories and causality in their dual gravity description. Our
discussion involves CFTs with different central charges whose description, in
the gravity side, requires the inclusion of quadratic curvature corrections. It
is enough, indeed, to consider the Gauss-Bonnet term. We find that both sides
of the AdS/CFT correspondence impose a restriction on the Gauss-Bonnet
coupling. In the case of 6d supersymmetric CFTs, we show the full matching of
these restrictions. We perform this computation in two ways. First by
considering a thermal setup in a black hole background. Second by scrutinizing
the scattering of gravitons with a shock wave in AdS. The different helicities
provide the corresponding lower and upper bounds. We generalize these results
to arbitrary higher dimensions and comment on some hints and puzzles they
prompt regarding the possible existence of higher dimensional CFTs and the
extent to which the AdS/CFT correspondence would be valid for them.Comment: 31 pages, 5 figures; v2: typos fixed, cosmetic amendments and
references adde
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