1,362 research outputs found
A Closer Look at Two Branes in an Bulk
We investigate a scenario with two branes in an bulk. In this
scenario there are two gravitons and we investigate the role played by each of
them for different positions of the second brane. We show that both gravitons
play a significant role only when the turn-around point in the warp factor is
approximately equidistant from both branes. We find that the ultralight mode
becomes heavy as the second brane approaches the turn-around point, and the
physics begins to resemble that of the RS model. Thus we demonstrate the
crucial role played by the turn-around in the warp factor in enabling the
presence of both gravitons.Comment: 21 pages, late
Bubbling Geometries for Half BPS Wilson lines
We consider the supergravity backgrounds that correspond to supersymmetric
Wilson line operators in the context of AdS/CFT correspondence. We study the
gravitino and dilatino conditions of the IIB supergravity under the appropriate
ansatz, and obtain some necessary conditions for a supergravity background that
preserves the same symmetry as the supersymmetric Wilson lines. The
supergravity solutions are characterized by continuous version of maya
diagrams. This diagram is related to the eigenvalue distribution of the
Gaussian matrix model. We also consider the similar backgrounds of the
11-dimensional supergravity.Comment: 25 pages, 9 figures. v2:typos corrected. v3:added the differential
conditions and comments at the end of section 2. typos correcte
On the sign of the dilaton in the soft wall models
We elaborate on the existence of a spurious massless scalar mode in the
vector channel of soft-wall models with incorrectly chosen sign of the
exponential profile defining the wall. We re-iterate the point made in our
earlier paper and demonstrate that the presence of the mode is robust,
depending only on the infra-red asymptotics of the wall. We also re-emphasize
that desired confinement properties can be realized with the correct sign
choice.Comment: 10 page
Polarization-sensitive absorption of THz radiation by interacting electrons in chirally stacked multilayer graphene
We show that opacity of a clean multilayer graphene flake depends on the
helicity of the circular polarized electromagnetic radiation. The effect can be
understood in terms of the pseudospin selection rules for the interband optical
transitions in the presence of exchange electron-electron interactions which
alter the pseudospin texture in momentum space. The interactions described
within a semi-analytical Hartree--Fock approach lead to the formation of the
topologically different broken--symmetry states characterized by Chern numbers
and zero-field anomalous Hall conductivities.Comment: 6 pages, final versio
Mesons from global Anti-de Sitter space
In the context of gauge/gravity duality, we study both probe D7-- and probe
D5--branes in global Anti-de Sitter space. The dual field theory is N=4 theory
on R x S^3 with added flavour. The branes undergo a geometrical phase
transition in this geometry as function of the bare quark mass m_q in units of
1/R with R the S^3 radius. The meson spectra are obtained from fluctuations of
the brane probes. First, we study them numerically for finite quark mass
through the phase transition. Moreover, at zero quark mass we calculate the
meson spectra analytically both in supergravity and in free field theory on R x
S^3 and find that the results match: For the chiral primaries, the lowest level
is given by the zero point energy or by the scaling dimension of the operator
corresponding to the fluctuations, respectively. The higher levels are
equidistant. Similar results apply to the descendents. Our results confirm the
physical interpretation that the mesons cannot pair-produce any further when
their zero-point energy exceeds their binding energy.Comment: 43 pages, 8 figures, references edited, few typos corrected, updated
to match the published versio
Heavy metals contaminating the environment of a progressive supranuclear palsy cluster induce tau accumulation and cell death in cultured neurons
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by the presence of intracellular aggregates of tau protein and neuronal loss leading to cognitive and motor impairment. Occurrence is mostly sporadic, but rare family clusters have been described. Although the etiopathology of PSP is unknown, mutations in the MAPT/tau gene and exposure to environmental toxins can increase the risk of PSP. Here, we used cell models to investigate the potential neurotoxic effects of heavy metals enriched in a highly industrialized region in France with a cluster of sporadic PSP cases. We found that iPSC-derived iNeurons from a MAPT mutation carrier tend to be more sensitive to cell death induced by chromium (Cr) and nickel (Ni) exposure than an isogenic control line. We hypothesize that genetic variations may predispose to neurodegeneration induced by those heavy metals. Furthermore, using an SH-SY5Y neuroblastoma cell line, we showed that both heavy metals induce cell death by an apoptotic mechanism. Interestingly, Cr and Ni treatments increased total and phosphorylated tau levels in both cell types, implicating Cr and Ni exposure in tau pathology. Overall, this study suggests that chromium and nickel could contribute to the pathophysiology of tauopathies such as PSP by promoting tau accumulation and neuronal cell death
AdS Branes Corresponding to Superconformal Defects
We investigate an AdS_4 x L_2 D5-brane in AdS_5 x X_5 space-time, in the
context of AdS/dCFT correspondence. Here, X_5 is a Sasaki-Einstein manifold and
L_2 is a submanifold of X_5. This brane has the same supersymmetry as the
3-dimensional N=1 superconformal symmetry if L_2 is a special Legendrian
submanifold in X_5. In this case, this brane is supposed to correspond to a
superconformal wall defect in 4-dimensional N=4 super Yang-Mills theory. We
construct these new string backgrounds and show they have the correct
supersymmetry, also in the case with non-trivial gauge flux on L_2. The
simplest new example is AdS_4 x T^2 brane in AdS_5 x S^5. We construct the
brane solution expressing the RG flow between two different defects. We also
perform similar analysis for an AdS_3 x L_3 M5-brane in AdS_4 x X_7, for a weak
G_2 manifold X_7 and its submanifold L_3. This system has the same
supersymmetry as 2-dimensional N=(1,0) global superconformal symmetry, if L_3
is an associative submanifold.Comment: 22 pages, LaTeX, 3 figures. v2: typos corrected, references added.
v3: typos correcte
The Spatial String Tension, Thermal Phase Transition, and AdS/QCD
We present results of modeling the temperature dependence of the spatial
string tension and thermal phase transition in a five-dimensional framework
nowadays known as AdS/QCD. For temperatures close to the critical one we find a
behaviour remarkably consistent with the lattice results.Comment: 8 pages, 4 figure
Mass and Gauge Invariance IV (Holography for the Karch-Randall Model)
We argue that the Karch-Randall compactification is holographically dual to a
4-d conformal field theory coupled to gravity on Anti de Sitter space. Using
this interpretation we recover the mass spectrum of the model. In particular,
we find no massless spin-2 states. By giving a purely 4-d interpretation to the
compactification we make clear that it represents the first example of a local
4-d field theory in which general covariance does not imply the existence of a
massless graviton. We also discuss some variations of the Karch-Randall model
discussed in the literature, and we examine whether its properties are generic
to all conformal field theory.Comment: 26 pages, uses package latexsym. Note added in proo
Vacuum Energy Density and Cosmological Constant in dS Brane World
We discuss the vacuum energy density and the cosmological constant of dS
brane world with a dilaton field. It is shown that a stable AdS brane can
be constructed and gravity localization can be realized. An explicit relation
between the dS bulk cosmological constant and the brane cosmological constant
is obtained. The discrete mass spectrum of the massive scalar field in the
AdS brane is used to acquire the relationship between the brane
cosmological constant and the vacuum energy density. The vacuum energy density
in the brane gotten by this method is in agreement with astronomical
observations.Comment: 16 pages,4 figure
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