1,693 research outputs found
Low-energy effective theory for a Randall-Sundrum scenario with a moving bulk brane
We derive the low-energy effective theory of gravity for a generalized
Randall-Sundrum scenario, allowing for a third self-gravitating brane to live
in the 5D bulk spacetime. At zero order the 5D spacetime is composed of two
slices of anti-de Sitter spacetime, each with a different curvature scale, and
the 5D Weyl tensor vanishes. Two boundary branes are at the fixed points of the
orbifold whereas the third brane is free to move in the bulk. At first order,
the third brane breaks the otherwise continuous evolution of the projection of
the Weyl tensor normal to the branes. We derive a junction condition for the
projected Weyl tensor across the bulk brane, and combining this constraint with
the junction condition for the extrinsic curvature tensor, allows us to derive
the first-order field equations on the middle brane. The effective theory is a
generalized Brans-Dicke theory with two scalar fields. This is conformally
equivalent to Einstein gravity and two scalar fields, minimally coupled to the
geometry, but nonminimally coupled to matter on the three branes.Comment: 16 pages, 1 figure, typos correcte
ANALYSIS OF INTERFACIAL AND MASS TRANSFER EFFECTS ON FORCED CONVECTION IN GAS-LIQUID ANNULAR TWO-PHASE FLOW
In a gas-liquid annular two-phase flow one of the main factors influencing
the determination of heat transfer rates is the average thickness of the liquid
film. A model to accurately represent the heat transfer in such situations has
to be able of determining the average liquid film thickness to within a
reasonable accuracy. A typical physical aspect in gas-liquid annular flows is
the appearance of interface waves, which affect heat, mass and momentum
transfers. Existing models implicitly consider the wave effects in the
momentum transfer by an empirical correlation for the interfacial friction
factor. However, this procedure does not point out the difference between
interface waves and the natural turbulent effects of the system. In the
present work, the wave and mass transfer effects in the theoretical
estimation of average liquid film thickness are analyzed, in comparison to a
model that does not explicitly include these effects, as applied to the
prediction of heat transfer rates in a thermally developing flow situation
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
Silicon Photo-Multiplier radiation hardness tests with a beam controlled neutron source
We report radiation hardness tests performed at the Frascati Neutron
Generator on silicon Photo-Multipliers, semiconductor photon detectors built
from a square matrix of avalanche photo-diodes on a silicon substrate. Several
samples from different manufacturers have been irradiated integrating up to
7x10^10 1-MeV-equivalent neutrons per cm^2. Detector performances have been
recorded during the neutron irradiation and a gradual deterioration of their
properties was found to happen already after an integrated fluence of the order
of 10^8 1-MeV-equivalent neutrons per cm^2.Comment: 7 pages, 6 figures, Submitted to Nucl. Inst. Meth.
Evaluation in Health: Reflections Inscribed in the Paradigm of Contemporary Health
Objectives: To analyze the methods of health evaluation from the point of view of users\u27 needs and the care perspective
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
Braneworld Flux Inflation
We propose a geometrical model of brane inflation where inflation is driven
by the flux generated by opposing brane charges and terminated by the collision
of the branes, with charge annihilation. We assume the collision process is
completely inelastic and the kinetic energy is transformed into the thermal
energy after collision. Thereafter the two branes coalesce together and behave
as a single brane universe with zero effective cosmological constant. In the
Einstein frame, the 4-dimensional effective theory changes abruptly at the
collision point. Therefore, our inflationary model is necessarily 5-dimensional
in nature. As the collision process has no singularity in 5-dimensional
gravity, we can follow the evolution of fluctuations during the whole history
of the universe. It turns out that the radion field fluctuations have a steeply
tilted, red spectrum, while the primordial gravitational waves have a flat
spectrum. Instead, primordial density perturbations could be generated by a
curvaton mechanism.Comment: 11 pages, 6 figures, references adde
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