2,599 research outputs found
Pathologies in Asymptotically Lifshitz Spacetimes
There has been significant interest in the last several years in studying
possible gravitational duals, known as Lifshitz spacetimes, to anisotropically
scaling field theories by adding matter to distort the asymptotics of an AdS
spacetime. We point out that putative ground state for the most heavily studied
example of such a spacetime, that with a flat spatial section, suffers from a
naked singularity and further point out this singularity is not resolvable by
any known stringy effect. We review the reasons one might worry that
asymptotically Lifshitz spacetimes are unstable and employ the initial data
problem to study the stability of such systems. Rather surprisingly this
question, and even the initial value problem itself, for these spacetimes turns
out to generically not be well-posed. A generic normalizable state will evolve
in such a way to violate Lifshitz asymptotics in finite time. Conversely,
enforcing the desired asymptotics at all times puts strong restrictions not
just on the metric and fields in the asymptotic region but in the deep interior
as well. Generically, even perturbations of the matter field of compact support
are not compatible with the desired asymptotics.Comment: 36 pages, 1 figure, v2: Enhanced discussion of singularity, including
relationship to Gubser's conjecture and singularity in RG flow solution, plus
minor clarification
Exploring How Eruption Source Parameters Affect Volcanic Radiative Forcing Using Statistical Emulation
The radiative forcing caused by a volcanic eruption is dependent on several eruption source parameters such as the mass of sulfur dioxide (SO2) emitted, the eruption column height, and the eruption latitude. General circulation models with prognostic aerosol and chemistry schemes can be used to investigate how each parameter influences the volcanic forcing. However, the range of multidimensional parameter space that can be explored is restricted because such simulations are computationally expensive. Here we use statistical emulation to explore the radiative impact of eruptions over a wide covarying range of SO2 emission magnitudes, injection heights, and eruption latitudes based on only 30 simulations. We use the emulators to build response surfaces to visualize and predict the sulfate aerosol e-folding decay time, the stratospheric aerosol optical depth, and net radiative forcing of thousands of different eruptions. We find that the volcanic stratospheric aerosol optical depth and net radiative forcing are primarily determined by the mass of SO2 emitted, but eruption latitude is the most important parameter in determining the sulfate aerosol e-folding decay time. The response surfaces reveal joint effects of the eruption source parameters in influencing the net radiative forcing, such as a stronger influence of injection height for tropical eruptions than high-latitude eruptions. We also demonstrate how the emulated response surfaces can be used to find all combinations of eruption source parameters that produce a particular volcanic response, often revealing multiple solutions
Thermodynamic instability of doubly spinning black objects
We investigate the thermodynamic stability of neutral black objects with (at
least) two angular momenta. We use the quasilocal formalism to compute the
grand canonical potential and show that the doubly spinning black ring is
thermodynamically unstable. We consider the thermodynamic instabilities of
ultra-spinning black objects and point out a subtle relation between the
microcanonical and grand canonical ensembles. We also find the location of the
black string/membrane phases of doubly spinning black objects.Comment: 25 pages, 7 figures v2: matches the published versio
The Itinerary of Autophagosomes: From Peripheral Formation to Kiss-and-Run Fusion with Lysosomes
Macroautophagy, a constitutive process in higher eukaryotic cells, mediates degradation of many long-lived proteins and organelles. The actual events occurring during the process in the dynamic system of a living cell have never been thoroughly investigated. We aimed to develop a live-cell assay in which to follow the complete itinerary of an autophagosome. Our experiments show that autophagosomes are formed randomly in peripheral regions of the cell. They then move bidirectionally along microtubules, accumulating at the microtubule-organizing centre, in a similar way to lysosomes. Their centripetal movement is dependent on the motor protein dynein and is important for their fusion with lysosomes. Initially, autophagosomes dock on to lysosomes, independent of lysosomal acidification. Two kinds of fusion then occur: complete fusions, creating a hybrid organelle, or more often kiss-and-run fusions, i.e. transfer of some content while still maintaining two separate vesicles. Surprisingly, the autophagolysosomal compartment seems to be more long lived than expected. Our study documents many aspects of autophagosome behaviour, adding to our understanding of the mechanism and control of autophagy. Indeed, although the formation of autophagosomes is completely different from any other vesicular structures, their later itinerary appears to be very similar to those of other trafficking pathways
Holography of Charged Dilaton Black Holes
We study charged dilaton black branes in . Our system involves a
dilaton coupled to a Maxwell field with dilaton-dependent
gauge coupling, . First, we find the solutions for
extremal and near extremal branes through a combination of analytical and
numerical techniques. The near horizon geometries in the simplest cases, where
, are Lifshitz-like, with a dynamical exponent
determined by . The black hole thermodynamics varies in an interesting
way with , but in all cases the entropy is vanishing and the specific
heat is positive for the near extremal solutions. We then compute conductivity
in these backgrounds. We find that somewhat surprisingly, the AC conductivity
vanishes like at T=0 independent of . We also explore the
charged black brane physics of several other classes of gauge-coupling
functions . In addition to possible applications in AdS/CMT, the
extremal black branes are of interest from the point of view of the attractor
mechanism. The near horizon geometries for these branes are universal,
independent of the asymptotic values of the moduli, and describe generic
classes of endpoints for attractor flows which are different from .Comment: 33 pages, 3 figures, LaTex; v2, references added; v3, more refs
added; v4, refs added, minor correction
Dynamics of Fundamental Matter in N=2* Yang-Mills Theory
We study the dynamics of quenched fundamental matter in
supersymmetric large SU(N) Yang-Mills theory at zero temperature. Our tools
for this study are probe D7-branes in the holographically dual
Pilch-Warner gravitational background. Previous work using
D3-brane probes of this geometry has shown that it captures the physics of a
special slice of the Coulomb branch moduli space of the gauge theory, where the
constituent D3-branes form a dense one dimensional locus known as the
enhancon, located deep in the infrared. Our present work shows how this physics
is supplemented by the physics of dynamical flavours, revealed by the D7-branes
embeddings we find. The Pilch-Warner background introduces new divergences into
the D7-branes free energy, which we are able to remove with a single
counterterm. We find a family of D7-brane embeddings in the geometry and
discuss their properties. We study the physics of the quark condensate,
constituent quark mass, and part of the meson spectrum. Notably, there is a
special zero mass embedding that ends on the enhancon, which shows that while
the geometry acts repulsively on the D7-branes, it does not do so in a way that
produces spontaneous chiral symmetry breaking.Comment: 24 pages, 8 figures. Corrected typos, added comment about
counterterm. To appear in JHE
Effective AdS/renormalized CFT
For an effective AdS theory, we present a simple prescription to compute the
renormalization of its dual boundary field theory. In particular, we define
anomalous dimension holographically as the dependence of the wave-function
renormalization factor on the radial cutoff in the Poincare patch of AdS. With
this definition, the anomalous dimensions of both single- and double- trace
operators are calculated. Three different dualities are considered with the
field theory being CFT, CFT with a double-trace deformation and spontaneously
broken CFT. For the second dual pair, we compute scaling corrections at the UV
and IR fixed points of the RG flow triggered by the double-trace deformation.
For the last case, we discuss whether our prescription is sensitive to the AdS
interior or equivalently, the IR physics of the dual field theory.Comment: 20 pages, 3 figure
Hairy planar black holes in higher dimensions
We construct exact hairy planar black holes in D-dimensional AdS gravity.
These solutions are regular except at the singularity and have stress-energy
that satisfies the null energy condition. We present a detailed analysis of
their thermodynamical properties and show that the first law is satisfied. We
also discuss these solutions in the context of AdS/CFT duality and construct
the associated c-function.Comment: 18 pages, no figures; v2: title changed, typos fixe
Giant magnons and non-maximal giant gravitons
We produce the open strings on that correspond to
the solutions of integrable boundary sine-Gordon theory by making use of the
-magnon solutions provided in \cite{KPV} together with explicit moduli.
Relating the two boundary parameters in a special way we describe the
scattering of giant magnons with non-maximal giant gravitons and
calculate the leading contribution to the associated magnon scattering phase.Comment: 34 pages, 8 figure
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