2,227 research outputs found
Cosmological constant in SUGRA models with Planck scale SUSY breaking and degenerate vacua
The empirical mass of the Higgs boson suggests small to vanishing values of the quartic Higgs self-coupling and the corresponding beta function at the Planck scale, leading to degenerate vacua. This leads us to suggest that the measured value of the cosmological constant can originate from supergravity (SUGRA) models with degenerate vacua. This scenario is realised if there are at least three exactly degenerate vacua. In the first vacuum, associated with the physical one, local supersymmetry (SUSY) is broken near the Planck scale while the breakdown of the SU(2)W×U(1)Y symmetry takes place at the electroweak (EW) scale. In the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than ΛQCD in the physical vacuum. Finally, in the third vacuum local SUSY and EW symmetry are broken near the Planck scale
Chiral aspects of hadron structure
Chiral loop corrections for hadronic properties are considered in a
constituent quark model. It is emphasized that the correct implementation of
such corrections requires a sum over intermediate hadronic states. The leading
non-analytic corrections are very important for baryon magnetic moments and
explain the failure of the sum rule
predicted by the
constituent quark model.Comment: 10 pages, latex, 2 ps figures, to appear in Phys. Lett.
On the -Distribution of Inclusively Produced Particles in Annihilation
We discuss the momentum distributions of inclusively produced particles in
annihilation. We show that the dependence of the position of the
maxima of the spectra on the mass of the produced particles
follows naturally from the general definition of fragmentation functions when
energy-momentum conservation is correctly incorporated
Incorporating Chiral Symmetry in Extrapolations of Octet Baryon Magnetic Moments
We explore methods of extrapolating lattice calculations of hadronic
observables to the physical regime, while respecting the constraints of chiral
symmetry and heavy quark effective theory. In particular, we extrapolate
lattice results for magnetic moments of the spin-1/2 baryon octet to the
physical pion mass and compare with experimental measurements. The success
previously reported for extrapolations of the nucleon magnetic moments carries
over to the Sigma baryons. A study of the residual discrepancies in the Xi
baryon moments suggests that it is important to have new simulation data with a
more realistic strange quark mass.Comment: 9 pages, 4 figure
Spectral change of sigma and omega mesons in a dense nuclear medium
The spectra of the scalar () and vector () mesons in nuclear
matter are studied in detail using the quark-meson coupling (QMC) model. It is
shown that above normal nuclear matter density the effects of -
mixing and the decay of the into change the spectra of
and mesons considerably. As in Quantum Hadrodynamics we find a
remarkable spectral change in the meson and the longitudinal mode of
the meson, namely a two-peak structure.Comment: 14 pages + 9 ps files for 4 figs. The paper was revised, and accepted
for publication in Physics Letters
Supporting the prescription of exercise in spinal cord injured populations
Following a spinal cord injury (SCI), participation in regular exercise can enhance physical capacity and performance in activities of daily living. With this in mind, the use of subjective ratings of perceived exertion (RPE) may provide an easy-to-administer alternative to traditional methods of regulating exercise intensity (e.g. heart rate and power output (PO). A physically active lifestyle is also associated with a reduced risk of cardiovascular disease, in part because exercise exerts anti-inflammatory effects. Examining the plasma response of inflammation-mediating chemical messengers, known as cytokines, to traditional and novel exercise modalities may help maximise the anti-inflammatory potential of regular exercise.
Participants with a cervical level SCI successfully self-regulated a 20 min bout of moderate intensity wheelchair propulsion (Chapter three). No differences in physiological or PO responses were observed during the imposed-intensity and self-regulated wheelchair propulsion in the trained population group. In a non-SCI group of novice wheelchair-users, a differentiated RPE specific to the exercising muscle mass (RPEP) was the dominant perceptual signal during submaximal wheelchair propulsion (Chapter four). The novice group successfully self-regulated a 12 min bout of moderate intensity wheelchair propulsion, comprising of a discontinuous 3 x 4 min protocol, using differentiated RPEP. In contrast, a more accurate self-regulation of light intensity wheelchair propulsion was observed when employing traditional overall RPE compared to RPEP.
Following strenuous wheelchair propulsion, plasma concentrations of the inflammation-mediating cytokine interleukin-6 (IL-6) were significantly elevated in non-SCI and thoracic level SCI participants (Chapter five). Impaired sympathetic nervous system (SNS) function was associated with a reduced IL-6 response in participants with a cervical level SCI. The plasma IL-6 response to 30 min moderate intensity (60% VO2peak) arm-crank ergometry (ACE) was associated with an elevation in the anti-inflammatory cytokine IL-1 receptor antagonist (IL-1ra) independent of SNS activation (Chapter six). Light intensity ACE resulted in a small, significant plasma IL-6 response but no IL-1ra response. The addition of functional electrical stimulation-evoked lower-limb cycling to concurrent hand cycling, termed hybrid exercise, resulted in a greater plasma IL-6 response compared to moderate intensity hand cycling alone in participants with a thoracic level SCI (Chapter seven)
Sigma and omega meson propagation in a dense nuclear medium
The propagation of the scalar () and vector () mesons in
nuclear matter is studied in detail using the Walecka model over a wide range
of densities and including the effects of a finite width through the
inclusion of a two-pion loop. We calculate the dispersion relation and spectral
functions of the and (transverse and longitudinal) mesons,
including the effect of - mixing in matter. It is shown that
the mixing effect is quite important in the propagation of the (longitudinal)
and mesons above normal nuclear matter density. We find that
there is a two-peak structure in the spectral function of the channel,
caused by - mixing.Comment: 17 pages including 6 ps files, submitted to Phys. Lett. B.
Acknowledgement is revise
Fermi matrix element with isospin breaking
Prompted by the level of accuracy now being achieved in tests of the
unitarity of the CKM matrix, we consider the possible modification of the Fermi
matrix element for the -decay of a neutron, including possible in-medium
and isospin violating corrections. While the nuclear modifications lead to very
small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected,
the effect of the mass difference on the conclusion concerning
is no longer insignificant. Indeed, we suggest that the correction to the value
of is at the level of
The neutron charge form factor in helium-3
In order to measure the charge form factor of the neutron, , one
needs to use a neutron bound in a nuclear target. We calculate the change in
the form factor for a neutron bound in , with respect to the free case,
using several versions of the quark meson coupling model. It is found that the
form factor may be suppressed by as much as 12% at with
respect to that of the free neutron.Comment: 13 pages including 2 ps figure
Antibodies to glycans dominate the host response to schistosome larvae and eggs: Is their role protective or subversive?
Multiple exposures of chimpanzees to the radiation-attenuated schistosome vaccine provoked a strong parasite-specific cellular and humoral immune response. Specific IgM and IgG were directed mainly against glycans on antigens released by cercariae; these were also cross-reactive with soluble antigens from larvae, adult worms, and eggs. Egg deposition was the major antigenic stimulus after challenge of vaccinated and control chimpanzees with normal parasites, eliciting strong antiglycan responses to egg secretions. Glycan epitopes recognized included LacdiNAc, fucosylated LacdiNAc, LewisX (weakly), and those on keyhole limpet hemocyanin. Antibodies to peptide epitopes became prominent only during the chronic phase of infection, as glycan-specific IgM and IgG decreased. Because of their intensity and cross-reactivity, the antiglycan responses resulting from infection could be a smoke screen to subvert the immune system away from more vulnerable larval peptide epitopes. Their occurrence in humans might explain the long time required for antischistosome immunity to build up after infection
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