831 research outputs found
Meson Thermalization in Various Dimensions
In gauge/gravity duality framework the thermalization of mesons in strongly
coupled (p+1)-dimensional gauge theories is studied for a general Dp-Dq system,
q>=p, using the flavour Dq-brane as a probe. Thermalization corresponds to the
horizon formation on the flavour Dq-brane. We calculate the thermalization
time-scale due to a time-dependent change in the baryon number chemical
potential, baryon injection in the field theory. We observe that for such a
general system it has a universal behaviour depending only on the t'Hooft
coupling constant and the two parameters which describe how we inject baryons
into the system. We show that this universal behaviour is independent of the
details of the theory whether it is conformal and/or supersymmetric.Comment: 26 pages, 2 figure
Jet quenching in hot strongly coupled gauge theories simplified
Theoretical studies of jet stopping in strongly-coupled QCD-like plasmas have
used gauge-gravity duality to find that the maximum stopping distance scales
like E^{1/3} for large jet energies E. In recent work studying jets that are
created by finite-size sources in the gauge theory, we found an additional
scale: the typical (as opposed to maximum) jet stopping distance scales like
(EL)^{1/4}, where L is the size of the space-time region where the jet is
created. In this paper, we show that the results of our previous, somewhat
involved computation in the gravity dual, and the (EL)^{1/4} scale in
particular, can be very easily reproduced and understood in terms of the
distance that high-energy particles travel in AdS_5-Schwarzschild space before
falling into the black brane. We also investigate how stopping distances depend
on the conformal dimension of the source operator used to create the jet.Comment: 30 pages, 10 figure
Measuring Black Hole Formations by Entanglement Entropy via Coarse-Graining
We argue that the entanglement entropy offers us a useful coarse-grained
entropy in time-dependent AdS/CFT. We show that the total von-Neumann entropy
remains vanishing even when a black hole is created in a gravity dual, being
consistent with the fact that its corresponding CFT is described by a
time-dependent pure state. We analytically calculate the time evolution of
entanglement entropy for a free Dirac fermion on a circle following a quantum
quench. This is interpreted as a toy holographic dual of black hole creations
and annihilations. It is manifestly free from the black hole information
problem.Comment: 25 pages, Latex, 8 figure
Non-equilibrium Dynamics of O(N) Nonlinear Sigma models: a Large-N approach
We study the time evolution of the mass gap of the O(N) non-linear sigma
model in 2+1 dimensions due to a time-dependent coupling in the large-
limit. Using the Schwinger-Keldysh approach, we derive a set of equations at
large which determine the time dependent gap in terms of the coupling.
These equations lead to a criterion for the breakdown of adiabaticity for slow
variation of the coupling leading to a Kibble-Zurek scaling law. We describe a
self-consistent numerical procedure to solve these large- equations and
provide explicit numerical solutions for a coupling which starts deep in the
gapped phase at early times and approaches the zero temperature equilibrium
critical point in a linear fashion. We demonstrate that for such a
protocol there is a value of the coupling where the gap
function vanishes, possibly indicating a dynamical instability. We study the
dependence of on both the rate of change of the coupling and
the initial temperature. We also verify, by studying the evolution of the mass
gap subsequent to a sudden change in , that the model does not display
thermalization within a finite time interval and discuss the implications
of this observation for its conjectured gravitational dual as a higher spin
theory in .Comment: 22 pages, 9 figures. Typos corrected, references rearranged and
added.v3 : sections rearranged, abstract modified, comment about Kibble-Zurek
scaling correcte
Electrified plasma in AdS/CFT correspondence
We construct new gravity backgrounds holographic dual to neutral plasma with
U(1) global symmetry in the presence of constant electric field, considering
its full back-reactions to the metric. As the electric field and the induced
current cause a net energy in-flow to the system, the plasma is continually
heated up and the corresponding gravity solution has an expanding horizon.
After proposing a consistent late-time expansion scheme, we present analytic
solutions in the scheme up to next-leading order, and our solutions are new
time-dependent solutions of 5D asymptotic AdS Einstein-Maxwell(-Chern-Simons)
theory. To extract dual CFT stress tensor and U(1) current from the solutions,
we perform a rigorous holographic renormalization of
Einstein-Maxwell-Chern-Simons theory including full back-reactions, which can
in itself be an interesting addition to literatures. As by-products, we obtain
interesting modifications of energy-momentum/current Ward identities due to the
U(1) symmetry and its triangle anomaly.Comment: 27 pages, no figure, v3, minor typos fixed, matches with published
versio
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Notch signaling regulates metabolic heterogeneity in glioblastoma stem cells.
Glioblastoma (GBM) stem cells (GSCs) reside in both hypoxic and vascular microenvironments within tumors. The molecular mechanisms that allow GSCs to occupy such contrasting niches are not understood. We used patient-derived GBM cultures to identify GSC subtypes with differential activation of Notch signaling, which co-exist in tumors but occupy distinct niches and match their metabolism accordingly. Multipotent GSCs with Notch pathway activation reside in perivascular niches, and are unable to entrain anaerobic glycolysis during hypoxia. In contrast, most CD133-expressing GSCs do not depend on canonical Notch signaling, populate tumors regardless of local vascularity and selectively utilize anaerobic glycolysis to expand in hypoxia. Ectopic activation of Notch signaling in CD133-expressing GSCs is sufficient to suppress anaerobic glycolysis and resistance to hypoxia. These findings demonstrate a novel role for Notch signaling in regulating GSC metabolism and suggest intratumoral GSC heterogeneity ensures metabolic adaptations to support tumor growth in diverse tumor microenvironments
Expression quantitative trait loci are highly sensitive to cellular differentiation state
Blood cell development from multipotent hematopoietic stem cells to specialized blood cells is accompanied by drastic changes in gene expression for which the triggers remain mostly unknown. Genetical genomics is an approach linking natural genetic variation to gene expression variation, thereby allowing the identification of genomic loci containing gene expression modulators (eQTLs). In this paper, we used a genetical genomics approach to analyze gene expression across four developmentally close blood cell types collected from a large number of genetically different but related mouse strains. We found that, while a significant number of eQTLs (365) had a consistent “static” regulatory effect on gene expression, an even larger number were found to be very sensitive to cell stage. As many as 1,283 eQTLs exhibited a “dynamic” behavior across cell types. By looking more closely at these dynamic eQTLs, we show that the sensitivity of eQTLs to cell stage is largely associated with gene expression changes in target genes. These results stress the importance of studying gene expression variation in well-defined cell populations. Only such studies will be able to reveal the important differences in gene regulation between different ce
Energy loss in a strongly coupled anisotropic plasma
We study the energy loss of a rotating infinitely massive quark moving, at
constant velocity, through an anisotropic strongly-coupled N=4 plasma from
holography. It is shown that, similar to the isotropic plasma, the energy loss
of the rotating quark is due to either the drag force or radiation with a
continuous crossover from drag-dominated regime to the radiation dominated
regime. We find that the anisotropy has a significant effect on the energy loss
of the heavy quark, specially in the crossover regime. We argue that the energy
loss due to radiation in anisotropic media is less than the isotropic case.
Interestingly this is similar to analogous calculations for the energy loss in
weakly coupled anisotropic plasma.Comment: 26+1 pages, 10 figures, typos fixe
Direct isotopic evidence of biogenic methane production and efflux from beneath a temperate glacier
The base of glaciers and ice sheets provide environments suitable for the production of methane. High pressure conditions beneath the impermeable ‘cap’ of overlying ice promote entrapment of methane reserves that can be released to the atmosphere during ice thinning and meltwater evacuation. However, contemporary glaciers and ice sheets are rarely accounted for as methane contributors through field measurements. Here, we present direct field-based evidence of methane production and release from beneath the Icelandic glacier Sólheimajökull, where geothermal activity creates sub-oxic conditions suited to methane production and preservation along the meltwater flow path. Methane production at the glacier bed (48 tonnes per day, or 39 mM CH4 m−2 day−1), and evasion to the atmosphere from the proglacial stream (41 tonnes per day, or 32 M CH4 m−2 day−1) indicates considerable production and release to the atmosphere during the summer melt season. Isotopic signatures (−60.2‰ to −7.6‰ for δ13CCH4 and −324.3‰ to +161.1‰ for DCH4), support a biogenic signature within waters emerging from the subglacial environment. Temperate glacial methane production and release may thus be a significant and hitherto unresolved contributor of a potent greenhouse gas to the atmosphere
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