386 research outputs found
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
Validation of the SCID-hu Thy/Liv mouse model with four classes of licensed antiretrovirals.
BackgroundThe SCID-hu Thy/Liv mouse model of HIV-1 infection is a useful platform for the preclinical evaluation of antiviral efficacy in vivo. We performed this study to validate the model with representatives of all four classes of licensed antiretrovirals.Methodology/principal findingsEndpoint analyses for quantification of Thy/Liv implant viral load included ELISA for cell-associated p24, branched DNA assay for HIV-1 RNA, and detection of infected thymocytes by intracellular staining for Gag-p24. Antiviral protection from HIV-1-mediated thymocyte depletion was assessed by multicolor flow cytometric analysis of thymocyte subpopulations based on surface expression of CD3, CD4, and CD8. These mice can be productively infected with molecular clones of HIV-1 (e.g., the X4 clone NL4-3) as well as with primary R5 and R5X4 isolates. To determine whether results in this model are concordant with those found in humans, we performed direct comparisons of two drugs in the same class, each of which has known potency and dosing levels in humans. Here we show that second-generation antiretrovirals were, as expected, more potent than their first-generation predecessors: emtricitabine was more potent than lamivudine, efavirenz was more potent than nevirapine, and atazanavir was more potent than indinavir. After interspecies pharmacodynamic scaling, the dose ranges found to inhibit viral replication in the SCID-hu Thy/Liv mouse were similar to those used in humans. Moreover, HIV-1 replication in these mice was genetically stable; treatment of the mice with lamivudine did not result in the M184V substitution in reverse transcriptase, and the multidrug-resistant NY index case HIV-1 retained its drug-resistance substitutions.ConclusionGiven the fidelity of such comparisons, we conclude that this highly reproducible mouse model is likely to predict clinical antiviral efficacy in humans
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
Black holes and black branes in Lifshitz spacetimes
We construct analytic solutions describing black holes and black branes in
asymptotically Lifshitz spacetimes with arbitrary dynamical exponent z and for
arbitrary number of dimensions. The model considered consists of Einstein
gravity with negative cosmological constant, a scalar, and N U(1) gauge fields
with dilatonic-like couplings. We study the phase diagrams and thermodynamic
instabilities of the solution, and find qualitative differences between the
cases with 12.Comment: 27 pages, 10 figures; v2 references added, minor comments adde
Effects of umbilical cord tissue mesenchymal stem cells (UCX®) on rat sciatic nerve regeneration after neurotmesis injuries
Conductivity and quasinormal modes in holographic theories
We show that in field theories with a holographic dual the retarded Green's
function of a conserved current can be represented as a convergent sum over the
quasinormal modes. We find that the zero-frequency conductivity is related to
the sum over quasinormal modes and their high-frequency asymptotics via a sum
rule. We derive the asymptotics of the quasinormal mode frequencies and their
residues using the phase-integral (WKB) approach and provide analytic insight
into the existing numerical observations concerning the asymptotic behavior of
the spectral densities.Comment: 24 pages, 3 figure
Non-Equilibrium Field Dynamics of an Honest Holographic Superconductor
Most holographic models of superconducting systems neglect the effects of
dynamical boundary gauge fields during the process of spontaneous
symmetry-breaking. Usually a global symmetry gets broken. This yields a
superfluid, which then is gauged "weakly" afterwards. In this work we build
(and probe the dynamics of) a holographic model in which a local boundary
symmetry is spontaneously broken instead. We compute two-point functions of
dynamical non-Abelian gauge fields in the normal and in the broken phase, and
find non-trivial gapless modes. Our AdS3 gravity dual realizes a p-wave
superconductor in (1+1) dimensions. The ground state of this model also breaks
(1+1)-dimensional parity spontaneously, while the Hamiltonian is
parity-invariant. We discuss possible implications of our results for a wider
class of holographic liquids.Comment: 32 pages, 12 figures; v3: string theory derivation of setup added
(section 3.1), improved presentation, version accepted by JHEP; v2: paragraph
added to discussion, figure added, references added, typos correcte
Non-equilibrium Condensation Process in a Holographic Superconductor
We study the non-equilibrium condensation process in a holographic
superconductor. When the temperature T is smaller than a critical temperature
T_c, there are two black hole solutions, the Reissner-Nordstrom-AdS black hole
and a black hole with a scalar hair. In the boundary theory, they can be
regarded as the supercooled normal phase and the superconducting phase,
respectively. We consider perturbations on supercooled Reissner-Nordstrom-AdS
black holes and study their non-linear time evolution to know about physical
phenomena associated with rapidly-cooled superconductors. We find that, for
T<T_c, the initial perturbations grow exponentially and, eventually, spacetimes
approach the hairy black holes. We also clarify how the relaxation process from
a far-from-equilibrium state proceeds in the boundary theory by observing the
time dependence of the superconducting order parameter. Finally, we study the
time evolution of event and apparent horizons and discuss their correspondence
with the entropy of the boundary theory. Our result gives a first step toward
the holographic understanding of the non-equilibrium process in
superconductors.Comment: 20 pages, 7 figure
Field theories with anisotropic scaling in 2D, solitons and the microscopic entropy of asymptotically Lifshitz black holes
Field theories with anisotropic scaling in 1+1 dimensions are considered. It
is shown that the isomorphism between Lifshitz algebras with dynamical
exponents z and 1/z naturally leads to a duality between low and high
temperature regimes. Assuming the existence of gap in the spectrum, this
duality allows to obtain a precise formula for the asymptotic growth of the
number of states with a fixed energy which depends on z and the energy of the
ground state, and reduces to the Cardy formula for z=1. The holographic
realization of the duality can be naturally inferred from the fact that
Euclidean Lifshitz spaces in three dimensions with dynamical exponents and
characteristic lengths given by z, l, and 1/z, l/z, respectively, are
diffeomorphic. The semiclassical entropy of black holes with Lifshitz
asymptotics can then be recovered from the generalization of Cardy formula,
where the ground state corresponds to a soliton. An explicit example is
provided by the existence of a purely gravitational soliton solution for BHT
massive gravity, which precisely has the required energy that reproduces the
entropy of the analytic asymptotically Lifshitz black hole with z=3.
Remarkably, neither the asymptotic symmetries nor central charges were
explicitly used in order to obtain these results.Comment: 17 pages, no figures, references corrected and update
Analytical study on holographic superconductors in external magnetic field
We investigate the holographic superconductors immersed in an external
magnetic field by using the analytical approach. We obtain the spatially
dependent condensate solutions in the presence of the magnetism and find
analytically that the upper critical magnetic field satisfies the relation
given in the Ginzburg-Landau theory. We observe analytically the reminiscent of
the Meissner effect where the magnetic field expels the condensate. Extending
to the D-dimensional Gauss-Bonnet AdS black holes, we examine the influence
given by the Gauss-Bonnet coupling on the condensation. Different from the
positive coupling, we find that the negative Gauss-Bonnet coupling enhances the
condensation when the external magnetism is not strong enough.Comment: revised version, to appear in JHE
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