1,422 research outputs found
The off-Shell Electromagnetic Vertex of the Nucleon in Chiral Perturbation Theory
We study the electromagnetic vertex of a nucleon in next-to-leading order
chiral perturbation theory (CPT). We consider the case where one of the
nucleons at the NN vertex is off its mass shell. We define relevant
measures for the off-shell dependence in the limited kinematical range allowed,
and analyze their expansion in the pion mass. The leading nonanalytic
contributions are calculated to estimate their size.Comment: 12 pages (LaTeX), 1 figure (available upon request), NIKHEF 93-P
Quasi-Local Density Functional Theory and its Application within Extended Thomas-Fermi Approximation
A generalization of the Density Functional Theory is proposed. The theory
developed leads to single-particle equations of motion with a quasi-local
mean-field operator, which contains a quasi-particle position-dependent
effective mass and a spin-orbit potential. The energy density functional is
constructed using the Extended Thomas-Fermi approximation. Within the framework
of this approach the ground-state properties of the doubly magic nuclei are
considered. The calculations have been performed using the finite-range Gogny
D1S force. The results are compared with the exact Hartree-Fock calculations
Constraints on Neutrino Parameters from Neutral-Current Solar Neutrino Measurements
We generalize the pull approach to define the function to the
analysis of the data with correlated statistical errors. We apply this method
to the analysis of the Sudbury Neutrino Collaboration data obtained in the
salt-phase. In the global analysis of all the solar neutrino and KamLAND data
we find the best fit (minimum ) values of neutrino parameters to be
and
eV. We confirm that the maximal mixing is strongly disfavored while the
bounds on are significantly strengthened.Comment: 6 figures. Some typos are corrected, figures are visually improve
Neutrino-Deuteron Scattering in Effective Field Theory at Next-to-Next-to Leading Order
We study the four channels associated with neutrino-deuteron breakup
reactions at next-to-next to leading order in effective field theory. We find
that the total cross-section is indeed converging for neutrino energies up to
20 MeV, and thus our calculations can provide constraints on theoretical
uncertainties for the Sudbury Neutrino Observatory. We stress the importance of
a direct experimental measurement to high precision in at least one channel, in
order to fix an axial two-body counterterm.Comment: 32 pages, 14 figures (eps
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The nature of impairments of memory in patients with end-stage renal disease (ESRD)
Possible impairments of memory in end-stage renal disease (ESRD) were investigated in two experiments. In Experiment 1, in which stimulus words were presented visually, participants were tested on conceptual or perceptual memory tasks, with retrieval being either explicit or implicit. Compared with healthy controls, ESRD patients were impaired when memory required conceptual but not when it required perceptual processing, regardless of whether retrieval was explicit or implicit. An impairment of conceptual implicit memory (priming) in the ESRD group represented a previously unreported deficit compared to healthy aging. There were no significant differences between pre- and immediate post-dialysis memory performance in ESRD patients on any of the tasks. In Experiment 2, in which presentation was auditory, patients again performed worse than controls on an explicit conceptual memory task. We conclude that the type of processing required by the task (conceptual vs. perceptual) is more important than the type of retrieval (explicit vs. implicit) in memory failures in ESRD patients, perhaps because temporal brain regions are more susceptible to the effects of the illness than are posterior regions
Food activities and identity maintenance in old age: a systematic review and meta-synthesis
This article has been made available through the Brunel Open Access Publishing Fund.Objectives: Services provided to older people should be developed based on active ageing policies. Nutrition is one aspect of active ageing, but little is known about how food activities contribute to psychological well-being in later life. This is a systematic review of qualitative and quantitative research that answers the question ‘What is known about the relationship between food activities and the maintenance of identities in old age?’
Effective theory of the Delta(1232) in Compton scattering off the nucleon
We formulate a new power-counting scheme for a chiral effective field theory
of nucleons, pions, and Deltas. This extends chiral perturbation theory into
the Delta-resonance region. We calculate nucleon Compton scattering up to
next-to-leading order in this theory. The resultant description of existing
p cross section data is very good for photon energies up to about 300
MeV. We also find reasonable numbers for the spin-independent polarizabilities
and .Comment: 29 pp, 9 figs. Minor revisions. To be published in PR
Proton-proton fusion in pionless effective theory
The proton-proton fusion reaction, , is studied in pionless
effective field theory (EFT) with di-baryon fields up to next-to leading order.
With the aid of the di-baryon fields, the effective range corrections are
naturally resummed up to the infinite order and thus the calculation is greatly
simplified. Furthermore, the low-energy constant which appears in the
axial-current-di-baryon-di-baryon contact vertex is fixed through the ratio of
two- and one-body matrix elements which reproduces the tritium lifetime very
precisely. As a result we can perform a parameter free calculation for the
process. We compare our numerical result with those from the accurate potential
model and previous pionless EFT calculations, and find a good agreement within
the accuracy better than 1%.Comment: 14 pages, 5 eps figure
Antihydrogen formation dynamics in a multipolar neutral anti-atom trap
Antihydrogen production in a neutral atom trap formed by an octupole-based
magnetic field minimum is demonstrated using field-ionization of weakly bound
anti-atoms. Using our unique annihilation imaging detector, we correlate
antihydrogen detection by imaging and by field-ionization for the first time.
We further establish how field-ionization causes radial redistribution of the
antiprotons during antihydrogen formation and use this effect for the first
simultaneous measurements of strongly and weakly bound antihydrogen atoms.
Distinguishing between these provides critical information needed in the
process of optimizing for trappable antihydrogen. These observations are of
crucial importance to the ultimate goal of performing CPT tests involving
antihydrogen, which likely depends upon trapping the anti-atom
Search For Trapped Antihydrogen
We present the results of an experiment to search for trapped antihydrogen
atoms with the ALPHA antihydrogen trap at the CERN Antiproton Decelerator.
Sensitive diagnostics of the temperatures, sizes, and densities of the trapped
antiproton and positron plasmas have been developed, which in turn permitted
development of techniques to precisely and reproducibly control the initial
experimental parameters. The use of a position-sensitive annihilation vertex
detector, together with the capability of controllably quenching the
superconducting magnetic minimum trap, enabled us to carry out a
high-sensitivity and low-background search for trapped synthesised antihydrogen
atoms. We aim to identify the annihilations of antihydrogen atoms held for at
least 130 ms in the trap before being released over ~30 ms. After a three-week
experimental run in 2009 involving mixing of 10^7 antiprotons with 1.3 10^9
positrons to produce 6 10^5 antihydrogen atoms, we have identified six
antiproton annihilation events that are consistent with the release of trapped
antihydrogen. The cosmic ray background, estimated to contribute 0.14 counts,
is incompatible with this observation at a significance of 5.6 sigma. Extensive
simulations predict that an alternative source of annihilations, the escape of
mirror-trapped antiprotons, is highly unlikely, though this possibility has not
yet been ruled out experimentally.Comment: 12 pages, 7 figure
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