7,063 research outputs found
Supergravity Inspired Warped Compactifications and Effective Cosmological Constants
We propose a supergravity inspired derivation of a Randall-Sundrum's type
action as an effective description of the dynamics of a brane coupled to the
bulk through gravity only. The cosmological constants in the bulk and on the
brane appear at the classical level when solving the equations of motion
describing the bosonic sector of supergravities in ten and eleven dimensions
coupled to the brane. They are related to physical quantities like the brane
electric charge and thus inherit some of their physical properties. The most
appealing property is their quantization: in d_\perp extra dimensions,
Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical
origin also explains the apparent fine-tuning required in the Randall-Sundrum
scenario. In our approach, the cosmological constants are derived parameters
and cannot be chosen arbitrarily; instead they are determined by the underlying
Lagrangian. Some of the branes we construct that support cosmological constant
in the bulk have supersymmetric properties: D3-branes of type IIB superstring
theory provide an explicit example.Comment: 17 pages, LaTeX, 1 figure. v2: references added and a comment about
D-8 brane of massive IIA sugra included v3: improved argument on the
effective cosmological constants quantization and clarified discussion on the
supersymmetric issue of the solutions constructed. Final version to appear in
NP
Kinetic description of fermion flavor mixing and CP-violating sources for baryogenesis
We derive transport equations for fermionic systems with a space-time
dependent mass matrix in flavor space allowing for complex elements leading to
CP violation required for electroweak baryogenesis. By constructing appropriate
projectors in flavor space of the relevant tree level Kadanoff-Baym equations,
we split the constraint equations into "diagonal" and "transversal" parts in
flavor space, and show that they decouple. While the diagonal densities exhibit
standard dispersion relations at leading order in gradients, the transverse
densities exhibit a novel on-shell structure. Next, the kinetic equations are
considered to second order in gradients and the CP-violating source terms are
isolated. This requires a thorough discussion of a flavor independent
definition of charge-parity symmetry operation. To make a link with
baryogenesis in the supersymmetric extension of the Standard Model, we
construct the Green functions for the leading order kinetic operator and solve
the kinetic equations for two mixing fermions (charginos). We take account of
flavor blind damping, and consider the cases of inefficient and moderate
diffusion. The resulting densities are the CP-violating chargino currents that
source baryogenesis.Comment: 33 pages, 6 figure
Computation of high Reynolds number internal/external flows
A general, user oriented computer program, called VNAF2, developed to calculate high Reynolds number internal/external flows is described. The program solves the two dimensional, time dependent Navier-Stokes equations. Turbulence is modeled with either a mixing length, a one transport equation, or a two transport equation model. Interior grid points are computed using the explicit MacCormack scheme with special procedures to speed up the calculation in the fine grid. All boundary conditions are calculated using a reference plane characteristic scheme with the viscous terms treated as source terms. Several internal, external, and internal/external flow calculations are presented
LANNDD---A Massive Liquid Argon Detector for Proton Decay, Supernova and Solar Neutrino Studies, and a Neutrino Factory Detector
We describe a possible Liquid Argon Neutrino and Nuclear Decay Detector
(LANNDD) that consists of a 70kt magnetized liquid argon tracking detector. The
detector is being designed for the Carlsbad Underground Laboratory.Comment: 8 pages, 5 figures; for the Neutrino Facory Meeting at KEK-NUFACT '0
Inflating Intersecting Branes and Remarks on the Hierarchy Problem
We generalize solutions of Einstein's equations for intersecting branes in
higher dimensional spacetimes to the nonstatic case, modeling an expanding
universe. The relation between the Hubble rate, the brane tensions, and the
bulk cosmological constant is similar to the case of a single 3-brane in a
5-dimensional spacetime. However, because the bulk inflates as well as the
branes, this class of solutions suffers from Newton's constant tending toward
zero on the TeV brane, where the Randall-Sundrum mechanism should solve the
weak scale hierarchy problem. The strength of gravity remains constant on the
Planck brane, however.Comment: 10 pages, LaTeX. v2:Misprint in eq. (23) corrected; citations fixed
and clarified relationship of our work to hep-th/9909053 and hep-th/9909076
v3: final version to appear in PLB. Corrected discussion of the time
dependance of the 4-D Planck mass on the TeV brane. Some references added to
earlier works on warped Kaluza-Klein compactification
Axial Currents from CKM Matrix CP Violation and Electroweak Baryogenesis
The first principle derivation of kinetic transport equations suggests that a
CP-violating mass term during the electroweak phase transition can induce axial
vector currents. Since the important terms are of first order in gradients
there is a possibility to construct new rephasing invariants that are
proportional to the CP phase in the Cabibbo-Kobayashi-Maskawa matrix and to
circumvent the upper bound of CP-violating contributions in the Standard Model,
the Jarlskog invariant. Qualitative arguments are given that these new
contributions still fail to explain electroweak baryogenesis in extensions of
the Standard Model with a strong first order phase transition.Comment: RevTeX, 8 pages, 6 figure
The Wild West No More: Preserving 40 Years of Electronic Records at the University of Wyoming American Heritage Center
The University of Wyoming American Heritage Center (AHC) provides access to all unrestricted collections, per its Mission Statement. However, over the past 40 years, the AHC has acquired born-digital collection material on physical media that it has been unable to provide access to. In the summer of 2014, the AHC undertook a project to migrate all born-digital records to a secure server, thereby creating the means to provide access to the material. After surveying collections databases and finding aids, the Digital Archivist and a graduate intern successfully ingested 346 pieces of digital media from 75 collections. The project was successful in largely eliminating the backlog of born-digital collection material and making those records available for use to all
A New Source for Electroweak Baryogenesis in the MSSM
One of the most experimentally testable explanations for the origin of the
baryon asymmetry of the universe is that it was created during the electroweak
phase transition, in the minimal supersymmetric standard model. Previous
efforts have focused on the current for the difference of the two Higgsino
fields, , as the source of biasing sphalerons to create the baryon
asymmetry. We point out that the current for the orthogonal linear combination,
, is larger by several orders of magnitude. Although this increases
the efficiency of electroweak baryogenesis, we nevertheless find that large
CP-violating angles are required to get a large enough baryon
asymmetry.Comment: 4 pages, 2 figures; numerical error corrected, which implies that
large CP violation is needed to get observed baryon asymmetry. We improved
solution of diffusion equations, and computed more accurate values for
diffusion coefficient and damping rate
A summary of recent NASA/Army contributions to rotorcraft vibrations and structural dynamics technology
The requirement for low vibrations has achieved the status of a critical design consideration in modern helicopters. There is now a recognized need to account for vibrations during both the analytical and experimental phases of design. Research activities in this area were both broad and varied and notable advances were made in recent years in the critical elements of the technology base needed to achieve the goal of a jet smooth ride. The purpose is to present an overview of accomplishments and current activities of govern and government-sponsored research in the area of rotorcraft vibrations and structural dynamics, focusing on NASA and Army contributions over the last decade or so. Specific topics addressed include: airframe finite-element modeling for static and dynamic analyses, analysis of coupled rotor-airframe vibrations, optimization of airframes subject to vibration constraints, active and passive control of vibrations in both the rotating and fixed systems, and integration of testing and analysis in such guises as modal analysis, system identification, structural modification, and vibratory loads measurement
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