4,778 research outputs found
Non-Local Effects of Multi-Trace Deformations in the AdS/CFT Correspondence
The AdS/CFT correspondence relates deformations of the CFT by "multi-trace
operators" to "non-local string theories". The deformed theories seem to have
non-local interactions in the compact directions of space-time; in the gravity
approximation the deformed theories involve modified boundary conditions on the
fields which are explicitly non-local in the compact directions. In this note
we exhibit a particular non-local property of the resulting space-time theory.
We show that in the usual backgrounds appearing in the AdS/CFT correspondence,
the commutator of two bulk scalar fields at points with a large enough distance
between them in the compact directions and a small enough time-like distance
between them in AdS vanishes, but this is not always true in the deformed
theories. We discuss how this is consistent with causality.Comment: 24 pages, 6 figures, 2 appendices. v2: added reference
Non-local string theories on AdS_3 times S^3 and stable non-supersymmetric backgrounds
We exhibit a simple class of exactly marginal "double-trace" deformations of
two dimensional CFTs which have AdS_3 duals, in which the deformation is given
by a product of left and right-moving U(1) currents. In this special case the
deformation on AdS_3 is generated by a local boundary term in three dimensions,
which changes the physics also in the bulk via bulk-boundary propagators.
However, the deformation is non-local in six dimensions and on the string
worldsheet, like generic non-local string theories (NLSTs). Due to the
simplicity of the deformation we can explicitly make computations in the
non-local string theory and compare them to CFT computations, and we obtain
precise agreement. We discuss the effect of the deformation on closed strings
and on D-branes. The examples we analyze include a supersymmetry-breaking but
exactly marginal "double-trace" deformation, which is dual to a string theory
in which no destabilizing tadpoles are generated for moduli nonperturbatively
in all couplings, despite the absence of supersymmetry. We explain how this
cancellation works on the gravity side in string perturbation theory, and also
non-perturbatively at leading order in the deformation parameter. We also
discuss possible flat space limits of our construction.Comment: 40 pages, 6 figures, harvma
Adaptive optics imaging of P Cygni in Halpha
We obtained Halpha diffraction limited data of the LBV star P Cyg using the
ONERA Adaptive Optics (AO) facility BOA at the OHP 1.52m telescope on October
1997. Taking P Cyg and the reference star 59 Cyg AO long exposures we find that
P Cyg clearly exhibits a large and diffuse intensity distribution compared to
the 59 Cyg's point-like source. A deconvolution of P Cyg using 59 Cyg as the
Point Spread Function was performed by means of the Richardson-Lucy algorithm.
P Cyg clearly appears as an unresolved star surrounded by a clumped envelope.
The reconstructed image of P Cyg is compared to similar spatial resolution maps
obtained from radio aperture synthesis imaging. We put independent constraints
on the physics of P Cyg which agree well with radio results. We discuss future
possibilities to constrain the wind structure of P Cyg by using
multi-resolution imaging, coronagraphy and long baseline interferometry to
trace back its evolutionary status.Comment: 10 pages, 19 Encapsulated Postscript figure
Intersubject Regularity in the Intrinsic Shape of Human V1
Previous studies have reported considerable intersubject variability in the three-dimensional geometry of the human primary visual cortex (V1). Here we demonstrate that much of this variability is due to extrinsic geometric features of the cortical folds, and that the intrinsic shape of V1 is similar across individuals. V1 was imaged in ten ex vivo human hemispheres using high-resolution (200 ÎĽm) structural magnetic resonance imaging at high field strength (7 T). Manual tracings of the stria of Gennari were used to construct a surface representation, which was computationally flattened into the plane with minimal metric distortion. The instrinsic shape of V1 was determined from the boundary of the planar representation of the stria. An ellipse provided a simple parametric shape model that was a good approximation to the boundary of flattened V1. The aspect ration of the best-fitting ellipse was found to be consistent across subject, with a mean of 1.85 and standard deviation of 0.12. Optimal rigid alignment of size-normalized V1 produced greater overlap than that achieved by previous studies using different registration methods. A shape analysis of published macaque data indicated that the intrinsic shape of macaque V1 is also stereotyped, and similar to the human V1 shape. Previoud measurements of the functional boundary of V1 in human and macaque are in close agreement with these results
Expectation values of twist fields and universal entanglement saturation of the free massive boson
The evaluation of vacuum expectation values (VEVs) in massive integrable
quantum field theory (QFT) is a nontrivial renormalization-group "connection
problem" -- relating large and short distance asymptotics -- and is in general
unsolved. This is particularly relevant in the context of entanglement entropy,
where VEVs of branch-point twist fields give universal saturation predictions.
We propose a new method to compute VEVs of twist fields associated to
continuous symmetries in QFT. The method is based on a differential equation in
the continuous symmetry parameter, and gives VEVs as infinite form-factor
series which truncate at two-particle level in free QFT. We verify the method
by studying U(1) twist fields in free models, which are simply related to the
branch-point twist fields. We provide the first exact formulae for the VEVs of
such fields in the massive uncompactified free boson model, checking against an
independent calculation based on angular quantization. We show that logarithmic
terms, overlooked in the original work of Callan and Wilczek [Phys. Lett. B333
(1994)], appear both in the massless and in the massive situations. This
implies that, in agreement with numerical form-factor observations by Bianchini
and Castro-Alvaredo [Nucl. Phys. B913 (2016)], the standard power-law
short-distance behavior is corrected by a logarithmic factor. We discuss how
this gives universal formulae for the saturation of entanglement entropy of a
single interval in near-critical harmonic chains, including log log
corrections.Comment: V2: 37 pages, explications and references adde
Quantum Black Hole Entropy, Localization and the Stringy Exclusion Principle
Supersymmetric localization has lead to remarkable progress in computing
quantum corrections to BPS black hole entropy. The program has been successful
especially for computing perturbative corrections to the Bekenstein-Hawking
area formula. In this work, we consider non-perturbative corrections related to
polar states in the Rademacher expansion, which describes the entropy in the
microcanonical ensemble. We propose that these non-perturbative effects can be
identified with a new family of saddles in the localization of the quantum
entropy path integral. We argue that these saddles, which are euclidean
geometries, arise after turning on singular fluxes
in M-theory on a Calabi-Yau. They cease to exist after a certain amount of
flux, resulting in a finite number of geometries; the bound on that number is
in precise agreement with the stringy exclusion principle. Localization of
supergravity on these backgrounds gives rise to a finite tail of Bessel
functions in agreement with the Rademacher expansion. As a check of our
proposal, we test our results against well-known microscopic formulas for
one-eighth and one-quarter BPS black holes in and
string theory respectively, finding agreement. Our method
breaks down precisely when mock-modular effects are expected in the entropy of
one-quarter BPS dyons and we comment upon this. Furthermore, we mention
possible applications of these results, including an exact formula for the
entropy of four dimensional black holes.Comment: 66 page
The Holographic Shape of Entanglement and Einstein's Equations
We study shape-deformations of the entanglement entropy and the modular
Hamiltonian for an arbitrary subregion and state (with a smooth dual geometry)
in a holographic conformal field theory. More precisely, we study a
double-deformation comprising of a shape deformation together with a state
deformation, where the latter corresponds to a small change in the bulk
geometry. Using a purely gravitational identity from the Hollands-Iyer-Wald
formalism together with the assumption of equality between bulk and boundary
modular flows for the original, undeformed state and subregion, we rewrite a
purely CFT expression for this double deformation of the entropy in terms of
bulk gravitational variables and show that it precisely agrees with the
Ryu-Takayanagi formula including quantum corrections. As a corollary, this
gives a novel, CFT derivation of the JLMS formula for arbitrary subregions in
the vacuum, without using the replica trick. Finally, we use our results to
give an argument that if a general, asymptotically AdS spacetime satisfies the
Ryu-Takayanagi formula for arbitrary subregions, then it must necessarily
satisfy the non-linear Einstein equation.Comment: 37 pages, 3 figure
Conformal Blocks Beyond the Semi-Classical Limit
Black hole microstates and their approximate thermodynamic properties can be
studied using heavy-light correlation functions in AdS/CFT. Universal features
of these correlators can be extracted from the Virasoro conformal blocks in
CFT2, which encapsulate quantum gravitational effects in AdS3. At infinite
central charge c, the Virasoro vacuum block provides an avatar of the black
hole information paradox in the form of periodic Euclidean-time singularities
that must be resolved at finite c.
We compute Virasoro blocks in the heavy-light, large c limit, extending our
previous results by determining perturbative 1/c corrections. We obtain
explicit closed-form expressions for both the `semi-classical'
and `quantum' corrections to the vacuum block, and we provide
integral formulas for general Virasoro blocks. We comment on the interpretation
of our results for thermodynamics, discussing how monodromies in Euclidean time
can arise from AdS calculations using `geodesic Witten diagrams'. We expect
that only non-perturbative corrections in 1/c can resolve the singularities
associated with the information paradox.Comment: 24+7 pages, 5 figures; v2 fixed typo in eq 2.22, added refs; v3 fixed
typo
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