147 research outputs found
AdS black disk model for small-x DIS
Using the approximate conformal invariance of QCD at high energies we
consider a simple AdS black disk model to describe saturation in DIS. Deep
inside saturation the structure functions have the same power law scaling, F_T
~ F_L ~ 1/x^w, where w is related to the expansion rate of the black disk with
energy. Furthermore, the ratio F_L /F_T is given by the universal value
(1+w)/(3+w), independently of the target. For virtual photon-photon scattering
at high energies we obtain explicit expressions and ratios for the total cross
sections of transverse and longitudinal photons in terms of the single
parameter w.Comment: 5 pages. Minor correction
Local bulk S-matrix elements and CFT singularities
We give a procedure for deriving certain bulk S-matrix elements from
corresponding boundary correlators. These are computed in the plane wave limit,
via an explicit construction of certain boundary sources that give bulk
wavepackets. A critical role is played by a specific singular behavior of the
lorentzian boundary correlators. It is shown in examples how correlators
derived from the bulk supergravity exhibit the appropriate singular structure,
and reproduce the corresponding S-matrix elements. This construction thus
provides a nontrivial test for whether a given boundary conformal field theory
can reproduce bulk physics, and where it does, supplies a prescription to
extract bulk S-matrix elements in the plane wave limit.Comment: 24 pages, 3 fig
Polarised black holes in ABJM
We numerically construct asymptotically solutions to
Einstein-Maxwell-dilaton theory. These have a dipolar electrostatic potential
turned on at the conformal boundary . We find two
classes of geometries: soliton solutions that encode the full
backreaction of the electric field on the geometry without a horizon, and
neutral black holes that are "polarised" by the dipolar potential. For a
certain range of the electric field , we find two distinct
branches of the soliton that exist for the same value of .
For the black hole, we find either two or four branches depending on the value
of the electric field and horizon temperature. These branches meet at critical
values of the electric field and impose a maximum value of that
should be reflected in the dual field theory. For both the soliton and black
hole geometries, we study boundary data such as the stress tensor. For the
black hole, we also consider horizon observables such as the entropy. At finite
temperature, we consider the Gibbs free energy for both phases and determine
the phase transition between them. We find that the soliton dominates at
low temperature for an electric field up to the maximum value. Using the
gauge/gravity duality, we propose that these solutions are dual to deformed
ABJM theory and compute the corresponding weak coupling phase diagram
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Polarised black holes in AdS
© 2016 IOP Publishing Ltd. We consider solutions in Einstein-Maxwell theory with a negative cosmological constant that asymptote to global AdS 4 with conformal boundary . At the sphere at infinity we turn on a space-dependent electrostatic potential, which does not destroy the asymptotic AdS behaviour. For simplicity we focus on the case of a dipolar electrostatic potential. We find two new geometries: (i) an AdS soliton that includes the full backreaction of the electric field on the AdS geometry; (ii) a polarised neutral black hole that is deformed by the electric field, accumulating opposite charges in each hemisphere. For both geometries we study boundary data such as the charge density and the stress tensor. For the black hole we also study the horizon charge density and area, and further verify a Smarr formula. Then we consider this system at finite temperature and compute the Gibbs free energy for both AdS soliton and black hole phases. The corresponding phase diagram generalizes the Hawking-Page phase transition. The AdS soliton dominates the low temperature phase and the black hole the high temperature phase, with a critical temperature that decreases as the external electric field increases. Finally, we consider the simple case of a free charged scalar field on with conformal coupling. For a field in the SU(N ) adjoint representation we compare the phase diagram with the above gravitational system
Nonlocality vs. complementarity: a conservative approach to the information problem
A proposal for resolution of the information paradox is that "nice slice"
states, which have been viewed as providing a sharp argument for information
loss, do not in fact do so as they do not give a fully accurate description of
the quantum state of a black hole. This however leaves an information
*problem*, which is to provide a consistent description of how information
escapes when a black hole evaporates. While a rather extreme form of
nonlocality has been advocated in the form of complementarity, this paper
argues that is not necessary, and more modest nonlocality could solve the
information problem. One possible distinguishing characteristic of scenarios is
the information retention time. The question of whether such nonlocality
implies acausality, and particularly inconsistency, is briefly addressed. The
need for such nonlocality, and its apparent tension with our empirical
observations of local quantum field theory, may be a critical missing piece in
understanding the principles of quantum gravity.Comment: 11 pages of text and figures, + references. v2 minor text. v3 small
revisions to match final journal versio
Holography from Conformal Field Theory
The locality of bulk physics at distances below the AdS length is one of the
remarkable aspects of AdS/CFT duality, and one of the least tested. It requires
that the AdS radius be large compared to the Planck length and the string
length. In the CFT this implies a large-N expansion and a gap in the spectum of
anomalous dimensions. We conjecture that the implication also runs in the other
direction, so that any CFT with a planar expansion and a large gap has a local
bulk dual. For an abstract CFT we formulate the consistency conditions, most
notably crossing symmetry, and show that the conjecture is true in a broad
range of CFT's, to first nontrivial order in 1/N^2: any CFT with a gap and a
planar expansion is generated via the AdS/CFT dictionary from a local bulk
interaction. We establish this result by a counting argument on each side, and
also investigate various properties of some explicit solutions.Comment: 49 pages. Minor corrections. Figure and references adde
Numerical tests of the large charge expansion
We perform Monte-Carlo measurements of two and three point functions of
charged operators in the critical O(2) model in 3 dimensions. Our results are
compatible with the predictions of the large charge superfluid effective field
theory. To obtain reliable measurements for large values of the charge, we
improved the Worm algorithm and devised a measurement scheme which mitigates
the uncertainties due to lattice and finite size effects.Comment: 16 pages, 12 figures. v2: Improved finite size scaling. v3: Added
comparison between Monte Carlo update
Coleman meets Schwinger
It is well known that spherical D-branes are nucleated in the presence of an
external RR electric field. Using the description of D-branes as solitons of
the tachyon field on non-BPS D-branes, we show that the brane nucleation
process can be seen as the decay of the tachyon false vacuum. This process can
describe the decay of flux-branes in string theory or the decay of quintessence
potentials arising in flux compactifications.Comment: 5 pages, 2 figure
Spinning Conformal Correlators
We develop the embedding formalism for conformal field theories, aimed at
doing computations with symmetric traceless operators of arbitrary spin. We use
an index-free notation where tensors are encoded by polynomials in auxiliary
polarization vectors. The efficiency of the formalism is demonstrated by
computing the tensor structures allowed in n-point conformal correlation
functions of tensors operators. Constraints due to tensor conservation also
take a simple form in this formalism. Finally, we obtain a perfect match
between the number of independent tensor structures of conformal correlators in
d dimensions and the number of independent structures in scattering amplitudes
of spinning particles in (d+1)-dimensional Minkowski space.Comment: 46 pages, 3 figures; V2: references added; V3: tiny misprint
corrected in (A.9
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