572 research outputs found
Worldsheet correlators in AdS(3)/CFT(2)
The AdS_3/CFT_2 correspondence is checked beyond the supergravity
approximation by comparing correlation functions. To this end we calculate 2-
and 3-point functions on the sphere of certain chiral primary operators for
strings on AdS_3 x S^3 x T^4. These results are then compared with the
corresponding amplitudes in the dual 2-dimensional conformal field theory. In
the limit of small string coupling, where the sphere diagrams dominate the
string perturbation series, beautiful agreement is found.Comment: 23 page
Massive Quantum Liquids from Holographic Angel's Trumpets
We explore the small-temperature regime in the deconfined phase of massive
fundamental matter at finite baryon number density coupled to the 3+1
dimensional N=4 SYM theory. In this setting, we can demonstrate a new type of
non-trivial temperature-independent scaling solutions for the probe brane
embeddings. Focusing mostly on matter supported in 2+1 dimensions, the
thermodynamics indicate that there is a quantum liquid with interesting
density-dependent low-temperature physics. We also comment about 3+1 and 1+1
dimensional systems, where we further find for example a new thermodynamic
instability.Comment: 18+1 pages, 6 figures; replaced fig. 6 and comments in sec. 5.2;
minor explanations added and typos fixed, final version published in JHEP
(modulo fig. 3); factor of \sqrt{\lambda} and corresponding comments fixe
High-level real-time programming in Java
Real-time systems have reached a level of complexity beyond the scaling capability of the low-level or restricted languages traditionally used for real-time programming. While Metronome garbage collection has made it practical to use Java to implement real-time systems, many challenges remain for the construction of complex real-time systems, some specic to the use of Java and others simply due to the change in scale of such systems. The goal of our research is the creation of a comprehensive Java-based programming environment and methodology for the creation of complex real-time systems. Our goals include construction of a provably correct real-time garbage collec-tor capable of providing worst case latencies of 100 s, capa-ble of scaling from sensor nodes up to large multiprocessors; specialized programming constructs that retain the safety and simplicity of Java, and yet provide sub-microsecond la-tencies; the extension of Java's \write once, run anywhere" principle from functional correctness to timing behavior; on-line analysis and visualization that aids in the understanding of complex behaviors; and a principled probabilistic analy-sis methodology for bounding the behavior of the resulting systems. While much remains to be done, this paper describes the progress we have made towards these goals
Radiation enhancement and "temperature" in the collapse regime of gravitational scattering
We generalize the semiclassical treatment of graviton radiation to
gravitational scattering at very large energies and finite
scattering angles , so as to approach the collapse regime of impact
parameters . Our basic tool is the
extension of the recently proposed, unified form of radiation to the ACV
reduced-action model and to its resummed-eikonal exchange. By superimposing
that radiation all-over eikonal scattering, we are able to derive the
corresponding (unitary) coherent-state operator. The resulting graviton
spectrum, tuned on the gravitational radius , fully agrees with previous
calculations for small angles but, for sizeable angles
acquires an exponential cutoff of the large
region, due to energy conservation, so as to emit a finite fraction
of the total energy. In the approach-to-collapse regime of we find
a radiation enhancement due to large tidal forces, so that the whole energy is
radiated off, with a large multiplicity and a
well-defined frequency cutoff of order .
The latter corresponds to the Hawking temperature for a black hole of mass
notably smaller than .Comment: 5 pages, 2 figures, talk presented at the European Physical Society
Conference on High Energy Physics, 5-12 July, Venice, Ital
Physical Response Functions of Strongly Coupled Massive Quantum Liquids
We study physical properties of strongly coupled massive quantum liquids from
their spectral functions using the AdS/CFT correspondence. The generic model
that we consider is dense, heavy fundamental matter coupled to SU(N_c) super
Yang-Mills theory at finite temperature above the deconfinement phase
transition but below the scale set by the baryon number density. In this setup,
we study the current-current correlators of the baryon number density using new
techniques that employ a scaling behavior in the dual geometry. Our results,
the AC conductivity, the quasi-particle spectrum and the Drude-limit parameters
like the relaxation time are simple temperature-independent expressions that
depend only on the mass-squared to density ratio and display a crossover
between a baryon- and meson-dominated regime. We concentrated on the
(2+1)-dimensional defect case, but in principle our results can also be
generalized straightforwardly to other cases.Comment: 21 pages, 10 figures, extra paragraph and figure are added in
response to referee's comment
Quasinormal modes of massive charged flavor branes
We present an analysis and classification of vector and scalar fluctuations
in a D3/D7 brane setup at finite termperature and baryon density. The system is
dual to an N=2 supersymmetric Yang-Mills theory with SU(N_c) gauge group and
N_f hypermultiplets in the fundamental representation in the quenched
approximation. We improve significantly over previous results on the
quasinormal mode spectrum of D7 branes and stress their novel physical
interpretation. Amongst our findings is a new purely imaginary scalar mode that
becomes tachyonic at sufficiently low temperature and baryon density. We
establish the existence of a critical density above which the scalar mode stays
in the stable regime for all temperatures. In the vector sector we study the
crossover from the hydrodynamic to the quasiparticle regime and find that it
moves to shorter wavelengths for lower temperatures. At zero baryon density the
quasinormal modes move toward distinct discrete attractor frequencies that
depend on the momentum as we increase the temperature. At finite baryon
density, however, the trajectories show a turning behavior such that for low
temperature the quasinormal mode spectrum approaches the spectrum of the
supersymmetric zero temperature normal modes. We interpret this as resolution
of the singular quasinormal mode spectrum that appears at the limiting D7 brane
embedding at vanishing baryon density.Comment: 56 pages, 40 figure
Pion and Vector Meson Form Factors in the Kuperstein-Sonnenschein holographic model
We study phenomenological aspects of the holographic model of chiral symmetry
breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first
step, we calculate the spectrum of vector and axial-vector mesons in the KS
model. We numerically compute various coupling constants of the mesons and
pions. Our analysis indicates that vector meson dominance is realized in this
model. The pion, vector meson and axial-vector meson form factors are obtained
and studied in detail. We find good agreement with QCD results. In particular,
the pion form factor closely matches available experimental data.Comment: v1: 27 pages, 9 figures, 4 tables; v2: minor changes, added more
general discussion of vector meson dominance; v3: minor changes and
additions, version accepted for publication in JHE
Sum Rules from an Extra Dimension
Using the gravity side of the AdS/CFT correspondence, we investigate the
analytic properties of thermal retarded Green's functions for scalars,
conserved currents, the stress tensor, and massless fermions. We provide some
results concerning their large and small frequency behavior and their pole
structure. From these results, it is straightforward to prove the validity of
various sum rules on the field theory side of the duality. We introduce a novel
contraction mapping we use to study the large frequency behavior of the Green's
functions.Comment: v2: 23 pages (plus appendix), revised presentation, discussion of
branch cuts moved to appendix, and some minor changes; v1: 24 pages (plus
appendix
Back-reaction of Non-supersymmetric Probes: Phase Transition and Stability
We consider back-reaction by non-supersymmetric D7/anti-D7 probe branes in
the Kuperstein-Sonnenschein model at finite temperature. Using the smearing
technique, we obtain an analytical solution for the back-reacted background to
leading order in N_f/N_c. This back-reaction explicitly breaks the conformal
invariance and introduces a dimension 6 operator in the dual field theory which
is an irrelevant deformation of the original conformal field theory. We further
probe this back-reacted background by introducing an additional set of probe
brane/anti-brane. This additional probe sector undergoes a chiral phase
transition at finite temperature, which is absent when the back-reaction
vanishes. We investigate the corresponding phase diagram and the thermodynamics
associated with this phase transition. We also argue that additional probes do
not suffer from any instability caused by the back-reaction, which suggests
that this system is stable beyond the probe limit.Comment: 56 pages, 8 figures. References updated, improved discussion on
dimension eight operato
Absolutely continuous spectrum for multi-type Galton Watson trees
We consider multi-type Galton Watson trees that are close to a tree of finite
cone type in distribution. Moreover, we impose that each vertex has at least
one forward neighbor. Then, we show that the spectrum of the Laplace operator
exhibits almost surely a purely absolutely continuous component which is
included in the absolutely continuous spectrum of the tree of finite cone type.Comment: to appear in Annales Henri Poincar\'
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