661 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
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
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
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
Holographic Evolution of Entanglement Entropy
We study the evolution of entanglement entropy in a 2-dimensional
equilibration process that has a holographic description in terms of a Vaidya
geometry. It models a unitary evolution in which the field theory starts in a
pure state, its vacuum, and undergoes a perturbation that brings it far from
equilibrium. The entanglement entropy in this set up provides a measurement of
the quantum entanglement in the system. Using holographic techniques we recover
the same result obtained before from the study of processes triggered by a
sudden change in a parameter of the hamiltonian, known as quantum quenches.
Namely, entanglement in 2-dimensional conformal field theories propagates with
velocity v^2=1. Both in quantum quenches and in the Vaidya model equilibration
is only achieved at the local level. Remarkably, the holographic derivation of
this last fact requires information from behind the apparent horizon generated
in the process of gravitational collapse described by the Vaidya geometry. In
the early stages of the evolution the apparent horizon seems however to play no
relevant role with regard to the entanglement entropy. We speculate on the
possibility of deriving a thermalization time for occupation numbers from our
analysis.Comment: 26 pages, 10 figure
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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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
The dynamics of quark-gluon plasma and AdS/CFT
In these pedagogical lectures, we present the techniques of the AdS/CFT
correspondence which can be applied to the study of real time dynamics of a
strongly coupled plasma system. These methods are based on solving
gravitational Einstein's equations on the string/gravity side of the AdS/CFT
correspondence. We illustrate these techniques with applications to the
boost-invariant expansion of a plasma system. We emphasize the common
underlying AdS/CFT description both in the large proper time regime where
hydrodynamic dynamics dominates, and in the small proper time regime where the
dynamics is far from equilibrium. These AdS/CFT methods provide a fascinating
arena interrelating General Relativity phenomenae with strongly coupled gauge
theory physics.Comment: 35 pages, 3 figures. Lectures at the 5th Aegean summer school, `From
gravity to thermal gauge theories: the AdS/CFT correspondence'. To appear in
the proceedings in `Lecture Notes in Physics
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
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