741 research outputs found
Topological regularization and self-duality in four-dimensional anti-de Sitter gravity
It is shown that the addition of a topological invariant (Gauss-Bonnet term)
to the anti-de Sitter (AdS) gravity action in four dimensions recovers the
standard regularization given by holographic renormalization procedure. This
crucial step makes possible the inclusion of an odd parity invariant
(Pontryagin term) whose coupling is fixed by demanding an asymptotic (anti)
self-dual condition on the Weyl tensor. This argument allows to find the dual
point of the theory where the holographic stress tensor is related to the
boundary Cotton tensor as , which
has been observed in recent literature in solitonic solutions and hydrodynamic
models.
A general procedure to generate the counterterm series for AdS gravity in any
even dimension from the corresponding Euler term is also briefly discussed.Comment: 13 pages, no figures; enlarged discussion on self-duality condition
for AAdS spacetimes, references added, final version for PR
Turning waves and breakdown for incompressible flows
We consider the evolution of an interface generated between two immiscible
incompressible and irrotational fluids. Specifically we study the Muskat and
water wave problems. We show that starting with a family of initial data given
by (\al,f_0(\al)), the interface reaches a regime in finite time in which is
no longer a graph. Therefore there exists a time where the solution of
the free boundary problem parameterized as (\al,f(\al,t)) blows-up: \|\da
f\|_{L^\infty}(t^*)=\infty. In particular, for the Muskat problem, this result
allows us to reach an unstable regime, for which the Rayleigh-Taylor condition
changes sign and the solution breaks down.Comment: 15 page
Spinning flavour branes and fermion pairing instabilities
We consider probe Dp-branes, p=3,5,7, in global AdS_5 x S^5, rotating along
an internal direction in the S^5. These are dual to strongly interacting N=4
SYM on S^3 with massless fundamental flavours, in the presence of an R-symmetry
chemical potential for flavour fermions. For massless, "AdS-filling" Dp-brane
embeddings at zero temperature, we find an infinite set of threshold values of
the chemical potential at which instabilities are triggered. The onset of
instability is always preceded by metastability of the zero density state. From
the onset values of the chemical potential, we infer that unstable directions
favour a homogeneous condensate of a bilinear made from fermion harmonics, or
Cooper pairing. We confirm this picture both numerically and analytically. The
linearized analysis showing the appearance of instabilities involves a charged
scalar in global AdS space coupled to a (large) constant background gauge
potential. The resulting frequency space correlator of the fermion bilinear at
strong coupling displays poles in the upper half plane. In contrast, the
correlator at zero coupling exhibits Pauli blocking due to occupation of states
below the Fermi level, but no instabilities. The end-point of the strong
coupling instability is not visible in our setup.Comment: 44 pages, 10 figures, uses late
Asymptotic perfect fluid dynamics as a consequence of AdS/CFT
We study the dynamics of strongly interacting gauge-theory matter (modelling
quark-gluon plasma) in a boost-invariant setting using the AdS/CFT
correspondence. Using Fefferman-Graham coordinates and with the help of
holographic renormalization, we show that perfect fluid hydrodynamics emerges
at large times as the unique nonsingular asymptotic solution of the nonlinear
Einstein equations in the bulk. The gravity dual can be interpreted as a black
hole moving off in the fifth dimension. Asymptotic solutions different from
perfect fluid behaviour can be ruled out by the appearance of curvature
singularities in the dual bulk geometry. Subasymptotic deviations from perfect
fluid behaviour remain possible within the same framework.Comment: 19 pages, 1 figure; v2: free streaming example changed to s=1;
conclusions unchange
Chiral Transition of N=4 Super Yang-Mills with Flavor on a 3-Sphere
We use the AdS/CFT correspondence to perform a numerical study of a phase
transition in strongly-coupled large-Nc N = 4 Super-Yang-Mills theory on a
3-sphere coupled to a finite number Nf of massive N = 2 hypermultiplets in the
fundamental representation of the gauge group. The gravity dual system is a
number Nf of probe D7-branes embedded in AdS_5 x S^5. We draw the phase diagram
for this theory in the plane of hypermultiplet mass versus temperature and
identify for temperatures above the Hawking-Page deconfinement temperature a
first-order phase transition line across which the chiral condensate jumps
discontinuously.Comment: 23 pages, 15 figures, minor corrections, reference added, nine
figures improved, no change in results or conclusions; expanded discussion of
fixing finite counterterms in section 3.3, figures updated, no changes to
conclusion
Cosmology from an AdS Schwarzschild black hole via holography
We derive the equations of cosmological evolution from an AdS Schwarzschild
black hole via holographic renormalization with appropriate boundary
conditions.Comment: 6 page
Early Time Dynamics in Heavy Ion Collisions from AdS/CFT Correspondence
We study the matter produced in heavy ion collisions assuming that this
matter is strongly interacting and employing AdS/CFT correspondence to
investigate its dynamics. At late proper times we show that Bjorken
hydrodynamics solution, obtained recently by Janik and Peschanski using
gauge-gravity duality [hep-th/0512162], can be singled out by simply requiring
that the metric tensor is a real and single-valued function of the coordinates
everywhere in the bulk, without imposing any constraints on the curvature
invariant. At early proper times we use similar strategy to show that the
energy density approaches a constant as proper time goes to zero. We therefore
demonstrate that the strong coupling dynamics incorporates the isotropization
transition in heavy ion collisions. By matching our early-time regime with the
late-time one of Janik and Peschanski we estimate the isotropization time at
RHIC to be approximately 0.3 fm/c, in good agreement with results of
hydrodynamic simulations.Comment: 24 pages, 2 figures; v2: some references added, minor typos correcte
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