1,209 research outputs found
Gravitational backreaction of anti-D branes in the warped compactification
We derive a low-energy effective theory for gravity with anti-D branes, which
are essential to get de Sitter solutions in the type IIB string warped
compactification, by taking account of gravitational backreactions of anti-D
branes. In order to see the effects of the self-gravity of anti-D branes, a
simplified model is studied where a 5-dimensional anti-de Sitter ({\it AdS})
spacetime is realized by the bulk cosmological constant and the 5-form flux,
and anti-D branes are coupled to the 5-form field by Chern-Simon terms. The
{\it AdS} spacetime is truncated by introducing UV and IR cut-off branes like
the Randall-Sundrum model. We derive an effective theory for gravity on the UV
brane and reproduce the familiar result that the tensions of the anti-D branes
give potentials suppressed by the forth-power of the warp factor at the
location of the anti-D branes. However, in this simplified model, the potential
energy never inflates the UV brane, although the anti-D-branes are inflating.
The UV brane is dominated by dark radiation coming from the projection of the
5-dimensional Weyl tensor, unless the moduli fields for the anti-D branes are
stabilized. We comment on the possibility of avoiding this problem in a
realistic string theory compactification.Comment: typos corrected, 11 pages, 3 figure
Numerical tests of AdS/CFT at strong coupling
We study various correlation functions (two and three point functions) in a
large matrix model of six commuting matrices with a numerical Monte Carlo
algorithm. This is equivalent to a model of a gas of particles in six
dimensions with a confining quadratic potential and logarithmic repulsions at
finite temperature, where we are measuring the leading order non-gaussianities
in the thermal fluctuations.
This is a simplified model of the low energy dynamics of N=4 SYM at strong
coupling. We find strong evidence that the simplified matrix model matches with
the dual gravitational description of three point functions in the AdS/CFT
correspondence.Comment: 23 pages, 7 figures, revtex. v2: minor correction
Enhanced Eshelby twist on thin wurtzite InP nanowires and measurement of local crystal rotation
We have performed a detailed study of the lattice distortions of InP wurtzite nanowires containing an axial screw dislocation. Eshelby predicted that this kind of system should show a crystal rotation due to the dislocation induced torque. We have measured the twisting rate and the dislocation Burgers vector on individual wires, revealing that nanowires with a 10-nm radius have a twist up to 100% larger than estimated from elasticity theory. The strain induced by the deformation has a Mexican-hat-like geometry, which may create a tube-like potential well for carriers
Constraints on the pMSSM from LAT Observations of Dwarf Spheroidal Galaxies
We examine the ability for the Large Area Telescope (LAT) to constrain
Minimal Supersymmetric Standard Model (MSSM) dark matter through a combined
analysis of Milky Way dwarf spheroidal galaxies. We examine the Lightest
Supersymmetric Particles (LSPs) for a set of ~71k experimentally valid
supersymmetric models derived from the phenomenological-MSSM (pMSSM). We find
that none of these models can be excluded at 95% confidence by the current
analysis; nevertheless, many lie within the predicted reach of future LAT
analyses. With two years of data, we find that the LAT is currently most
sensitive to light LSPs (m_LSP < 50 GeV) annihilating into tau-pairs and
heavier LSPs annihilating into b-bbar. Additionally, we find that future LAT
analyses will be able to probe some LSPs that form a sub-dominant component of
dark matter. We directly compare the LAT results to direct detection
experiments and show the complementarity of these search methods.Comment: 24 pages, 9 figures, submitted to JCA
The BF Formalism for QCD and Quark Confinement
Using the BF version of pure Yang-Mills, it is possible to find a covariant
representation of the 't Hooft magnetic flux operator. In this framework, 't
Hooft's pioneering work on confinement finds an explicit realization in the
continuum. Employing the Abelian projection gauge we compute the expectation
value of the magnetic variable and find the expected perimeter law. We also
check the area law behaviour for the Wilson loop average and compute the string
tension which turns out to be of the right order of magnitude.Comment: Various changes, version to appear in Nucl.Phys.
Flow dynamics and mixing past pairs of confined microfluidic cylinders
Placing cylindrical obstacles in a micromixer is a promising means to enhance mass transport. However, there is still a lack of fundamental understanding on the effect of obstacle arrangement on the flow. The present work provides new experimental insights into confined inertia flows past two cylindrical pins, placed either in tandem or staggered arrangement in a Y-type micromixer, and their effect on mixing, through micro Particle Image Velocimetry (ÎĽPIV) and Laser Induced Fluorescence (ÎĽLIF) measurements. It is found that in such confined microfluidic environments, adding a second pin suppresses vortex-shedding for spacings less than 3.5-pin diameters in a tandem arrangement or 0.25-pin diameters in the staggered configurations. Vortex-shedding is found to enhance mixing in tandem configurations but not in staggered ones. The results highlight the important roles of both pin arrangement and flow instabilities in micromixer performance and can serve as a guide to micromixer design
E 1 Gap Of Wurtzite Inas Single Nanowires Measured By Means Of Resonant Raman Spectroscopy
Indium arsenide nanowires were synthesized with an intermixing of wurtzite and zincblende structure by chemical beam epitaxy with the vapor-liquid-solid mechanism. Resonant Raman spectroscopy of the transverse optical phonon mode at 215cm -1 reveals an E 1 gap of 2.47 eV which is assigned to the electronic band gap at the A point in the indium arsenide wurtzite phase. © 2011 American Institute of Physics.1399473474 Int. Union Pure Appl. Phys. (IUPAP C8 Comm.),Korean Ministry of Education, Science and Technology,Seoul Metropolitan Government,Office of Naval Research Global,Korea Tourism OrganizationDick, K.A., (2008) Prog. Cryst. Growth Charact. Mater., 54, pp. 138-173Milnes, A.G., Polyakov, A.Y., (1993) Mater. Sci. Eng. B, 18, pp. 237-259Dayeh, S.A., Susac, D., Kavanagh, K.L., Yu, E.T., Wang, D., (2009) Adv. Mater., 19, pp. 2102-2108Cardona, M., (1961) J. Appl. Phys., 32 (SUPPL.), pp. 2151-2155Antoci, S., Reguzzoni, E., Samoggia, G., (1970) Phys. Rev. Lett., 24, pp. 1304-1307Arguello, C.A., Rousseau, D.L., Porto, S.P.S., (1969) Phys. Rev., 181, pp. 1351-136
The Donaldson-Witten Invariants in Pure QCD with Order and Disorder 't Hooft-like Operators
We study the first-order formalism of pure four-dimensional
Yang--Mills theory with theta-term. We describe the Green functions associated
to electric and magnetic flux operators \`a la 't~Hooft by means of
gauge-invariant non-local operators. These Green functions are related to
Witten's invariants of four-manifolds.Comment: 12 pages, LaTeX file, no macros used. Revised Versio
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