13,911 research outputs found
Low Energy Constants from High Energy Theorems
New constraints on resonance saturation in chiral perturbation theory are
investigated. These constraints arise because each consistent saturation scheme
must map to a representation of the full QCD chiral symmetry group. The
low-energy constants of chiral perturbation theory are then related by a set of
mixing angles. It is shown that vector meson dominance is a consequence of the
fact that nature has chosen the lowest-dimensional nontrivial chiral
representation. It is further shown that chiral symmetry places an upper bound
on the mass of the lightest scalar in the hadron spectrum.Comment: 11 pages TeX and mtexsis.te
Four Dimensional Supergravity from String Theory
A derivation of N=1 supergravity action from string theory is presented.
Starting from a Nambu-Goto bosonic string, matter field is introduced to obtain
a superstring in four dimension. The excitation quanta of this string contain
graviton and the gravitino. Using the principle of equivalence, the action in
curved space time are found and the sum of them is the Deser-Zumino N=1
supergravity action. The energy tensor is Lorentz invariant due to
supersymmetry.Comment: 9 page
Calculation of two- and three-dimensional transonic cascade flow field using the Navier-Stokes equations
A Navier-Stokes analysis employing the time-dependent Linearized Block Implicit scheme (LBI) was applied to two-dimensional and three-dimensional transonic turbulent cascade flows. In general, the geometrical configuration of the turbine blade impacts both the grid construction procedure and the implementation of the numerical algorithm. Since modern turbine blades of interest are characterized by very blunt leading edges, rounded trailing edges and high stacking angles, a robust grid construction procedure is required that can accommodate the severe body shape while resolving regions of large flow gradients. A constructive O-type grid generation technique, suitable for cascades with rounded trailing edges, was developed and used to construct the C3X turbine cascade coordinate grid. Two-dimensional calculations were performed employing the Navier-Stokes procedure for the C3X turbine cascade, and the predicted pressure coefficients and heat transfer rates were compared with the experimental data. Three-dimensional Navier-Stokes calculations were also performed
Using Perturbative Least Action to Recover Cosmological Initial Conditions
We introduce a new method for generating initial conditions consistent with
highly nonlinear observations of density and velocity fields. Using a variant
of the Least Action method, called Perturbative Least Action (PLA), we show
that it is possible to generate several different sets of initial conditions,
each of which will satisfy a set of highly nonlinear observational constraints
at the present day. We then discuss a code written to test and apply this
method and present the results of several simulations.Comment: 24 pages, 6 postscript figures. Accepted for publication in
Astrophysical Journa
Building an IT Taxonomy with Co-occurrence Analysis, Hierarchical Clustering, and Multidimensional Scaling
Different information technologies (ITs) are related in complex ways. How can the relationships among a large number of ITs be described and analyzed in a representative, dynamic, and scalable way? In this study, we employed co-occurrence analysis to explore the relationships among 50 information technologies discussed in six magazines over ten years (1998-2007). Using hierarchical clustering and multidimensional scaling, we have found that the similarities of the technologies can be depicted in hierarchies and two-dimensional plots, and that similar technologies can be classified into meaningful categories. The results imply reasonable validity of our approach for understanding technology relationships and building an IT taxonomy. The methodology that we offer not only helps IT practitioners and researchers make sense of numerous technologies in the iField but also bridges two related but thus far largely separate research streams in iSchools - information management and IT management
Self-force on a scalar charge in radial infall from rest using the Hadamard-WKB expansion
We present an analytic method based on the Hadamard-WKB expansion to
calculate the self-force for a particle with scalar charge that undergoes
radial infall in a Schwarzschild spacetime after being held at rest until a
time t = 0. Our result is valid in the case of short duration from the start.
It is possible to use the Hadamard-WKB expansion in this case because the value
of the integral of the retarded Green's function over the particle's entire
past trajectory can be expressed in terms of two integrals over the time period
that the particle has been falling. This analytic result is expected to be
useful as a check for numerical prescriptions including those involving mode
sum regularization and for any other analytical approximations to self-force
calculations.Comment: 22 pages, 2 figures, Physical Review D version along with the
corrections given in the erratu
Physical decomposition of the gauge and gravitational fields
Physical decomposition of the non-Abelian gauge field has recently solved the
two-decade-lasting problem of a meaningful gluon spin. Here we extend this
approach to gravity and attack the century-lasting problem of a meaningful
gravitational energy. The metric is unambiguously separated into a pure
geometric term which contributes null curvature tensor, and a physical term
which represents the true gravitational effect and always vanishes in a flat
space-time. By this decomposition the conventional pseudo-tensors of the
gravitational stress-energy are easily rescued to produce definite physical
result. Our decomposition applies to any symmetric tensor, and has interesting
relation to the transverse-traceless (TT) decomposition discussed by Arnowitt,
Deser and Misner, and by York.Comment: 11 pages, no figure; significant revision, with discussion on
relations of various metric decomposition
Scale-dependent bias of galaxies and mu-type distortion of the cosmic microwave background spectrum from single-field inflation with a modified initial state
We investigate the phenomenological consequences of a modification of the
initial state of a single inflationary field. While single-field inflation with
the standard Bunch-Davies initial vacuum state does not generally produce a
measurable three-point function (bispectrum) in the squeezed configuration,
allowing for a non-standard initial state produces an exception. Here, we
calculate the signature of an initial state modification in single-field
slow-roll inflation in both the scale-dependent bias of the large-scale
structure (LSS) and mu-type distortion in the black-body spectrum of the cosmic
microwave background (CMB). We parametrize the initial state modifications and
identify certain choices of parameters as natural, though we also note some
fine-tuned choices that can yield a larger bispectrum. In both cases, we
observe a distinctive k^-3 signature in LSS (as opposed to k^-2 for the
local-form). As a non-zero bispectrum in the squeezed configuration correlates
a long-wavelength mode with two short-wavelength modes, it induces a
correlation between the CMB temperature anisotropy on large scales with the
temperature-anisotropy-squared on very small scales; this correlation persists
as the small-scale anisotropy-squared is processed into mu-type distortions.
While the local-form mu-distortion turns out to be too small to detect in the
near future, a modified initial vacuum state enhances the signal by a large
factor owing to an extra factor of k_1/k. For example, a proposed
absolutely-calibrated experiment, PIXIE, is expected to detect this correlation
with a signal-to-noise ratio greater than 10, for an occupation number of about
0.5 in the observable modes. Relatively calibrated experiments such as Planck
and LiteBIRD should also be able to measure this effect, provided that the
relative calibration between different frequencies meets the required
precision. (Abridged)Comment: 14 pages, 6 figures. Matches version in PRD. Improved explanation in
Sec. IV; added references and corrected typo
Turbine Vane External Heat Transfer. Volume 2. Numerical Solutions of the Navier-stokes Equations for Two- and Three-dimensional Turbine Cascades with Heat Transfer
The application of the time-dependent ensemble-averaged Navier-Stokes equations to transonic turbine cascade flow fields was examined. In particular, efforts focused on an assessment of the procedure in conjunction with a suitable turbulence model to calculate steady turbine flow fields using an O-type coordinate system. Three cascade configurations were considered. Comparisons were made between the predicted and measured surface pressures and heat transfer distributions wherever available. In general, the pressure predictions were in good agreement with the data. Heat transfer calculations also showed good agreement when an empirical transition model was used. However, further work in the development of laminar-turbulent transitional models is indicated. The calculations showed most of the known features associated with turbine cascade flow fields. These results indicate the ability of the Navier-Stokes analysis to predict, in reasonable amounts of computation time, the surface pressure distribution, heat transfer rates, and viscous flow development for turbine cascades operating at realistic conditions
Self-interacting Elko dark matter with an axis of locality
This communication is a natural and nontrivial continuation of the 2005 work
of Ahluwalia and Grumiller on Elko. Here we report that Elko breaks Lorentz
symmetry in a rather subtle and unexpected way by containing a `hidden'
preferred direction. Along this preferred direction, a quantum field based on
Elko enjoys locality. In the form reported here, Elko offers a mass dimension
one fermionic dark matter with a quartic self-interaction and a preferred axis
of locality. The locality result crucially depends on a judicious choice of
phases.Comment: 14 pages (RevTex
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