K_{l3} transition form factors

The rainbow truncation of the quark Dyson-Schwinger equation is combined with the ladder Bethe-Salpeter equation for the meson bound state amplitudes and the dressed quark-W vertex in a manifestly covariant calculation of the K_{l3} transition form factors and decay width in impulse approximation. With model gluon parameters previously fixed by the chiral condensate, the pion mass and decay constant, and the kaon mass, our results for the K_{l3} form factors and the kaon semileptonic decay width are in good agreement with the experimental data.Comment: 8 pages, 3 figures, Revte

Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine Splittings

We investigate the chiral extrapolation of the lattice data for the light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region for the light quark mass. The chiral loop corrections providing non-analytic behavior in m_\pi are consistent with chiral perturbation theory for heavy mesons. Since chiral loop corrections tend to decrease the already too low splittings obtained from linear extrapolation, we investigate two models to guide the form of the analytic background behavior: the constituent quark potential model, and the covariant model of QCD based on the ladder-rainbow truncation of the Dyson-Schwinger equations. The extrapolated hyperfine splittings remain clearly below the experimental values even allowing for the model dependence in the description of the analytic background.Comment: 14 pages, 4 figures, typos corrected, presentation clarifie

Interleukin-10 plays an early role in generating virus-specific T cell anergy

<p>Abstract</p> <p>Background</p> <p>Infection of mice with the Armstrong strain of lymphocytic choriomeningitis virus (LCMV_ARM) leads to a robust immune response and efficient viral clearance. This is in contrast to infection with the variant strain LCMV_Clone13, which causes functional inactivation of effector T cells and viral persistence. The mechanism by which LCMV_Clone13suppresses the antiviral immune response and persists in its host is unknown.</p> <p>Results</p> <p>Here we demonstrate that infection with LCMV_Clone13, but not with LCMV_ARM, resulted in a steady increase in the serum levels of the immuno-inhibitory cytokine, IL-10. Blockade of IL-10 using neutralizing monoclonal antibody injections in LCMV_Clone13-infected mice led to dramatically enhanced effector T cell responses at 8 days post-infection. Even though IL-10 blockade resulted in decreased viral titers, the generation and maintenance of memory T cells was still compromised. The functional inactivation of CD8⁺T cells in IL-10-blocked, chronically infected mice 30 days post-infection was incomplete as potent CTL (cytotoxic T lymphocytes) could be generated by <it>in vitro </it>re-stimulation. IL-10 knockout mice showed a similar pattern of antiviral CD8 T cell responses: early antiviral T cells were dramatically increased and viral levels were decreased; however, CD8 T cells in IL-10 knockout mice were also eventually anergized and these mice became persistently infected.</p> <p>Conclusion</p> <p>Our data suggest that IL-10 plays an early role in LCMV_Clone13-induced tolerance, although other factors collaborate with IL-10 to induce virus-specific tolerance.</p

Electron in a transverse harmonic cavity

We employ Hamiltonian light-front quantum field theory in a basis function approach to solve the non-perturbative problem of an electron in a strong scalar transverse confining potential. We evaluate both the invariant mass spectra and the anomalous magnetic moment of the lowest state for this two-scale system. The weak external field limit of the anomalous magnetic moment agrees with the result of QED perturbation theory within the anticipated accuracy.Comment: 4 pages, 3 figures, published versio

Path integral Monte Carlo simulation of helium at negative pressures

Path integral Monte Carlo (PIMC) simulations of liquid helium at negative pressure have been carried out for a temperature range from the critical temperature to below the superfluid transition. We have calculated the temperature dependence of the spinodal line as well as the pressure dependence of the isothermal sound velocity in the region of the spinodal. We discuss the slope of the superfluid transition line and the shape of the dispersion curve at negative pressures.Comment: 6 pages, 7 figures, submitted to Physical Review B Revised: new reference, replaced figure

The π\pi, K+K^+, and K0K^0 electromagnetic form factors

The rainbow truncation of the quark Dyson-Schwinger equation is combined with the ladder Bethe-Salpeter equation for the meson amplitudes and the dressed quark-photon vertex in a self-consistent Poincar\'e-invariant study of the pion and kaon electromagnetic form factors in impulse approximation. We demonstrate explicitly that the current is conserved in this approach and that the obtained results are independent of the momentum partitioning in the Bethe-Salpeter amplitudes. With model gluon parameters previously fixed by the condensate, the pion mass and decay constant, and the kaon mass, the charge radii and spacelike form factors are found to be in good agreement with the experimental data.Comment: 8 pages, 6 figures, Revte

Quark-Exchange Mechanism of γd→np\gamma d \to np Reaction At 2-6 GeV

Within the constituent quark model, we examine the extent to which the deuteron photo-disintegration at 2-6 GeV can be described by the quark-exchange mechanism. With the parameters constrained by the $np$ scattering, the calculated differential cross sections disagree with the data in both magnitude and energy-dependence. The results can be improved if we use a smaller size parameter for quark wavefunctions. We also find that the on-shell approximation used in a previous investigation is not accurateComment: To be published in the Proceeeding of Second Asia Pacific Conference on Few-Body Problems in Physics, Shanghai, China, August 27-30, 200

Gaseous optical contamination of the spacecraft environment: A review

Interactions between the ambient atmosphere and orbiting spacecraft, sounding rockets, and suborbital vehicles, and with their effluents, give rise to optical (extreme UV to LWIR) foreground radiation which constitutes noise that raises the detection threshold for terrestrial and celestial radiations, as well as military targets. Researchers review the current information on the on-orbit optical contamination. Its source species are created in interaction processes that can be grouped into three categories: (1) Reactions in the gas phase between the ambient atmosphere and desorbates and exhaust; (2) Reactions catalyzed by exposed ram surfaces, which occur spontaneously even in the absence of active material releases from the vehicles; and (3) Erosive excitative reactions with exposed bulk (organic) materials, which have recently been identified in the laboratory though not as yet observed on spacecraft. Researchers also assess the effect of optical pumping by earthshine and sunlight of both reaction products and effluents

Dynamic sound attenuation at hypersonic frequencies in silica glass

In order to clarify the origin of the dominant processes responsible for the acoustic attenuation of phonons, which is a much debatted topic, we present Bril louin scattering experiments in various silica glasses of different OH impurities content. A large temperature range, from 5 to 1500 K is investigated, up to the glass transition temperature. Comparison of the hypersonic wave attenuation in various samples allows to identify two different processes. The first one induce s a low temperature peak related to relaxational processes; it is strongly sensitive to the extrinsic defects. The second, dominant in the hig h temperature range, is weakly dependent on the impurities and can be ascribed to anharmonic interactions