9,902 research outputs found
Search for missing baryon resonances via associated strangeness photoproduction
Differential cross-section and single polarization observables in the process
gamma p --> K^+ Lambda are investigated within a constituent quark model and a
dynamical coupled-channel formalism. The effects of two new nucleon resonances
and of the K*(892)- and K1(1270)-exchanges are briefly presented.Comment: Contributed paper to the IVth International Conference on Quarks and
Nuclear Physics, Madrid June 5-10, 200
Kids' Share 2010: Report on Federal Expenditures on Children
Examines 1960-2009 trends in federal spending and tax expenditures on children, including food stamps, tax credits, and Head Start. Analyzes the effects of American Recovery and Reinvestment Act funding, projected funding through 2020, and implications
How Targeted Are Federal Expenditures on Children? A Kids' Share Analysis of Expenditures by Income in 2009
Analyzes the distribution of government spending on children by family income; category, such as health, social services, and education; and program, such as Medicaid; and the extent to which it is targeted to low-income children. Considers implications
U-duality (sub-)groups and their topology
We discuss some consequences of the fact that symmetry groups appearing in
compactified (super-)gravity may be non-simply connected. The possibility to
add fermions to a theory results in a simple criterion to decide whether a
3-dimensional coset sigma model can be interpreted as a dimensional reduction
of a higher dimensional theory. Similar criteria exist for higher dimensional
sigma models, though less decisive. Careful examination of the topology of
symmetry groups rules out certain proposals for M-theory symmetries, which are
not ruled out at the level of the algebra's. We conclude with an observation on
the relation between the ``generalized holonomy'' proposal, and the actual
symmetry groups resulting from E_10 and E_11 conjectures.Comment: LaTeX, 8 pages, 2 tables, 1 figure, uses IOP-style files. Contributed
to the proceedings of the RTN-workshop ``The quantum structure of space-time
and the geometrical nature of the fundamental interactions,'', Copenhagen,
Denmark, september 200
Currents and Superpotentials in classical gauge theories: II. Global aspects and the example of Affine gravity
The conserved charges associated to gauge symmetries are defined at a
boundary component of space-time because the corresponding Noether current can
be rewritten on-shell as the divergence of a superpotential. However, the
latter is afflicted by ambiguities. Regge and Teitelboim found a procedure to
lift the arbitrariness in the Hamiltonian framework. An alternative covariant
formula was proposed by one of us for an arbitrary variation of the
superpotential, it depends only on the equations of motion and on the gauge
symmetry under consideration. Here we emphasize that in order to compute the
charges, it is enough to stay at a boundary of spacetime, without requiring any
hypothesis about the bulk or about other boundary components, so one may speak
of holographic charges. It is well known that the asymptotic symmetries that
lead to conserved charges are really defined at infinity, but the choice of
boundary conditions and surface terms in the action and in the charges is
usually determined through integration by parts whereas each component of the
boundary should be considered separately. We treat the example of gravity (for
any space-time dimension, with or without cosmological constant), formulated as
an Affine theory which is a natural generalization of the Palatini and
Cartan-Weyl (vielbein) first order formulations. We then show that the
superpotential associated to a Dirichlet boundary condition on the metric (the
one needed to treat asymptotically flat or AdS spacetimes) is the one proposed
by Katz, Bi\u{c}{\'a}k and Lynden-Bell and not that of Komar. We finally
discuss the KBL superpotential at null infinity.Comment: 16 pages, minor corrections and references added. Final version to
appear in CQ
E_11 and M Theory
We argue that eleven dimensional supergravity can be described by a
non-linear realisation based on the group E_{11}. This requires a formulation
of eleven dimensional supergravity in which the gravitational degrees of
freedom are described by two fields which are related by duality. We show the
existence of such a description of gravity.Comment: 21 pages, some typos corrected and two references adde
Symmetries,Singularities and the De-Emergence of Space
Recent work has revealed intriguing connections between a
Belinsky-Khalatnikov-Lifshitz-type analysis of spacelike singularities in
General Relativity and certain infinite dimensional Lie algebras, and in
particular the `maximally extended' hyperbolic Kac--Moody algebra E10. In this
essay we argue that these results may lead to an entirely new understanding of
the (quantum) nature of space(-time) at the Planck scale, and hence -- via an
effective `de-emergence' of space near a singularity -- to a novel mechanism
for achieving background independence in quantum gravity.Comment: 10 page
Dynamical Coupled-Channels Effects on Pion Photoproduction
The electromagnetic pion production reactions are investigated within the
dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193
(2007)}. The meson-baryon channels included in this study are , , , and the , and resonant components
of the channel. With the hadronic parameters of the model determined
in a recent study of scattering, we show that the pion photoproduction
data up to the second resonance region can be described to a very large extent
by only adjusting the bare helicity amplitudes, while the
non-resonant electromagnetic couplings are taken from previous works. It is
found that the coupled-channels effects can contribute about 10 - 20 % of the
production cross sections in the (1232) resonance region, and can
drastically change the magnitude and shape of the cross sections in the second
resonance region. The importance of the off-shell effects in a dynamical
approach is also demonstrated. The meson cloud effects as well as the
coupled-channels contributions to the form factors are found
to be mainly in the low region. For the magnetic M1
(1232) form factor, the results are close to that of the Sato-Lee Model.
Necessary improvements to the model and future developments are discussed.Comment: Corrected version. 14 pages, 10 figure
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