550 research outputs found
Holographic Screens and Transport Coefficients in the Fluid/Gravity Correspondence
We consider in the framework of the fluid/gravity correspondence the dynamics
of hypersurfaces located in the holographic radial direction at r = r_0. We
prove that these hypersurfaces evolve, to all orders in the derivative
expansion and including all higher curvature corrections, according to the same
hydrodynamics equations with identical transport coefficients. The analysis is
carried out for normal fluids as well as for superfluids. Consequently, this
proves the exactness of the bulk viscosity formula derived in arXiv:1103.1657
via the null horizon dynamics.Comment: 4 pages; v2: added clarifying comments and references; v3: added
comment about dependence of bulk viscosity formula on full equilibrium
solution, not only horizon dat
Macbeth
analysis done 1998, revised 2002. Some scenes I would now characterise as extrusionsand I would switch Lady Macbeth's entrance in 2.2 to the inwards door. Despite Banquo's references in 2.1 that would place her elsewhere than Duncan's chambers, she now suddenly appears from there, having 'laid their daggers ready' (2.2.11). A surprise re-entrance as in Antony and Cleopatra 1.2
Static post-Newtonian equivalence of GR and gravity with a dynamical preferred frame
A generally covariant extension of general relativity (GR) in which a
dynamical unit timelike vector field is coupled to the metric is studied in the
asymptotic weak field limit of spherically symmetric static solutions. The two
post-Newtonian parameters known as the Eddington-Robertson-Schiff parameters
are found to be identical to those in the case of pure GR, except for some
non-generic values of the coefficients in the Lagrangian.Comment: 13 pages; v.2: minor editing, signs corrected, version to appear in
PRD; v. 3: signs corrected in eqn (3
CFT dual of the AdS Dirichlet problem: Fluid/Gravity on cut-off surfaces
We study the gravitational Dirichlet problem in AdS spacetimes with a view to
understanding the boundary CFT interpretation. We define the problem as bulk
Einstein's equations with Dirichlet boundary conditions on fixed timelike
cut-off hypersurface. Using the fluid/gravity correspondence, we argue that one
can determine non-linear solutions to this problem in the long wavelength
regime. On the boundary we find a conformal fluid with Dirichlet constitutive
relations, viz., the fluid propagates on a `dynamical' background metric which
depends on the local fluid velocities and temperature. This boundary fluid can
be re-expressed as an emergent hypersurface fluid which is non-conformal but
has the same value of the shear viscosity as the boundary fluid. The
hypersurface dynamics arises as a collective effect, wherein effects of the
background are transmuted into the fluid degrees of freedom. Furthermore, we
demonstrate that this collective fluid is forced to be non-relativistic below a
critical cut-off radius in AdS to avoid acausal sound propagation with respect
to the hypersurface metric. We further go on to show how one can use this
set-up to embed the recent constructions of flat spacetime duals to
non-relativistic fluid dynamics into the AdS/CFT correspondence, arguing that a
version of the membrane paradigm arises naturally when the boundary fluid lives
on a background Galilean manifold.Comment: 71 pages, 2 figures. v2: Errors in bulk metrics dual to
non-relativistic fluids (both on cut-off surface and on the boundary) have
been corrected. New appendix with general results added. Fixed typos. 82
pages, 2 figure
The universal viscosity to entropy density ratio from entanglement
We present evidence that the universal Kovtun-Son-Starinets shear viscosity
to entropy density ratio of 1/4\pi can be associated with a Rindler causal
horizon in flat spacetime. Since there is no known holographic (gauge/gravity)
duality for this spacetime, a natural microscopic explanation for this
viscosity is in the peculiar properties of quantum entanglement. In particular,
it is well-known that the Minkowski vacuum state is a thermal state and carries
an area entanglement entropy density in the Rindler spacetime. Based on the
fluctuation-dissipation theorem, we expect a similar notion of viscosity
arising from vacuum fluctuations. Therefore, we propose a holographic Kubo
formula in terms of a two-point function of the stress tensor of matter fields
in the bulk. We calculate this viscosity assuming a minimally coupled scalar
field theory and find that the ratio with respect to the entanglement entropy
density is exactly 1/4\pi in four dimensions. The issues that arise in
extending this result to non-minimally coupled scalar fields, higher spins, and
higher dimensions provide interesting hints about the relationship between
entanglement entropy and black hole entropy.Comment: 30 pages; v2: footnote added, minor editin
Two approaches to testing general relativity in the strong-field regime
Observations of compact objects in the electromagnetic spectrum and the
detection of gravitational waves from them can lead to quantitative tests of
the theory of general relativity in the strong-field regime following two very
different approaches. In the first approach, the general relativistic field
equations are modified at a fundamental level and the magnitudes of the
potential deviations are constrained by comparison with observations. In the
second approach, the exterior spacetimes of compact objects are parametrized in
a phenomenological way, the various parameters are measured observationally,
and the results are finally compared against the general relativistic
predictions. In this article, I discuss the current status of both approaches,
focusing on the lessons learned from a large number of recent investigations.Comment: To appear in the proceedings of the conference New Developments in
Gravit
The holographic fluid dual to vacuum Einstein gravity
We present an algorithm for systematically reconstructing a solution of the
(d+2)-dimensional vacuum Einstein equations from a (d+1)-dimensional fluid,
extending the non-relativistic hydrodynamic expansion of Bredberg et al in
arXiv:1101.2451 to arbitrary order. The fluid satisfies equations of motion
which are the incompressible Navier-Stokes equations, corrected by specific
higher derivative terms. The uniqueness and regularity of this solution is
established to all orders and explicit results are given for the bulk metric
and the stress tensor of the dual fluid through fifth order in the hydrodynamic
expansion. We establish the validity of a relativistic hydrodynamic description
for the dual fluid, which has the unusual property of having a vanishing
equilibrium energy density. The gravitational results are used to identify
transport coefficients of the dual fluid, which also obeys an interesting and
exact constraint on its stress tensor. We propose novel Lagrangian models which
realise key properties of the holographic fluid.Comment: 31 pages; v2: references added and minor improvements, published
versio
Cosmological evolution of interacting dark energy in Lorentz violation
The cosmological evolution of an interacting scalar field model in which the
scalar field interacts with dark matter, radiation, and baryon via Lorentz
violation is investigated. We propose a model of interaction through the
effective coupling . Using dynamical system analysis, we study the
linear dynamics of an interacting model and show that the dynamics of critical
points are completely controlled by two parameters. Some results can be
mentioned as follows. Firstly, the sequence of radiation, the dark matter, and
the scalar field dark energy exist and baryons are sub dominant. Secondly, the
model also allows the possibility of having a universe in the phantom phase
with constant potential. Thirdly, the effective gravitational constant varies
with respect to time through . In particular, we consider a simple
case where has a quadratic form and has a good agreement with the
modified CDM and quintessence models. Finally, we also calculate the
first post--Newtonian parameters for our model.Comment: 14 pages, published versio
Anomalies in Superfluids and a Chiral Electric Effect
We analyze the chiral transport terms in relativistic superfluid
hydrodynamics. In addition to the spontaneously broken symmetry current, we
consider an arbitrary number of unbroken symmetries and extend the results of
arXiv:1105.3733. We suggest an interpretation of some of the new transport
coefficients in terms of chiral and gravitational anomalies. In particular, we
show that with unbroken gauged charges in the system, one can observe a chiral
electric conductivity - a current in a perpendicular direction to the applied
electric field. We present a motivated proposal for the value of the associated
transport coefficient, linking it to the triangle anomaly. Along the way we
present new arguments regarding the interpretation of the anomalous transport
coefficients in normal fluids. We propose a natural generalization of the
chiral transport terms to the case of an arbitrary number of spontaneously
broken symmetry currents.Comment: 30 pages; v2: Onsager-relations argument corrected, references added;
v3: fixed missing line in eq. (38
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