The soft-gluon limit and the infrared enhancement of the quark-gluon vertex

The Schwinger-Dyson quark equation (SDE) combined with results from lattice simulation for the propagators are used to obtain information on the quark-gluon vertex, taking into account the recent full QCD lattice results for the soft-gluon limit. Its inclusion leads to a clear enhancement of the infrared quark-gluon vertex. We also find that the relative contribution of the quark-ghost kernel to the quark-gluon vertex in the infrared region does not follow the rules from the perturbative analysis of the ultraviolet region. This shows that for QCD the intuition based on perturbation theory does not apply to the full momentum range. The framework developed in the current work provides analytical expressions for all the longitudinal components of vertex taken into account

Dynamical mass generation in Minkowski space at QCD scale

We undertake the challenging task to reveal the properties of dressed light-quarks in the space- and time-like regions. For that aim, we solved the Dyson-Schwinger equation (DSE) in Minkowski space for the quark propagator in a QCD inspired model, focusing on the realization of dynamical chiral symmetry breaking (DCSB) in the large coupling regime. The DSE is considered in the quenched approximation within the rainbow-ladder truncation with a massive gluon and a Pauli-Villars term, which is used to tune the infrared (IR) physics of the model. The solution of the DSE in Minkowski space is performed by resorting to the integral representation of the quark self-energy and propagator, which leads to a coupled set of closed self-consistent equations for the spectral densities, taking into account finite on-mass-shell renormalization. The parameters of the model are chosen such that the gluon mass scale is consistent with recent lattice QCD (LQCD) calculations, the Pauli-Villars mass is lowered down to about 1 GeV to concentrate strength in the infrared momentum region, and the coupling constant and renormalized mass are tuned to reproduce LQCD results for the quark mass function in the Landau gauge. Future application to study the pion consistently with DCSB within the Bethe-Salpeter framework with self-energies in Minkowski space is also delineated.Comment: 11 pages, 5 figure

Dynamical holographic QCD with area-law confinement and linear Regge trajectories

We construct a new solution of five-dimensional gravity coupled to a dilaton which encodes essential features of holographic QCD backgrounds dynamically. In particular, it implements linear confinement, i.e. the area law behavior of the Wilson loop, by means of a dynamically deformed anti-de Sitter metric. The predicted square masses of the light-flavored natural-parity mesons and their excitations lie on linear trajectories of approximately universal slope with respect to both radial and spin quantum numbers and are in satisfactory agreement with experimental data.Comment: 5 pages, 1 figure (vs2 contains an improved dilaton-gravity solution which generates trajectories of approximately universal slope

A dynamical holographic QCD model for spontaneous chiral symmetry breaking and confinement

In this paper, we present a holographic realization of spontaneous chiral symmetry breaking and confinement. The latter is realized by building a solution of 5d Einstein-dilaton gravity leading to a confining quark antiquark potential. The 4d currents and the quark mass operator associated with chiral symmetry breaking and creation of meson states are mapped to 5d fields whose dynamics is given by a non-Abelian Higgs action. We introduce a non-minimal dilaton coupling to the tachyon potential which has two parameters, one of them controlling the presence or absence of spontaneous chiral symmetry breaking and the other controlling the sign of the chiral condensate as the quark mass grows. We calculate the masses of vector, scalar, axial-vector and pseudoscalar mesons, focusing on the effect of chiral symmetry breaking on the spectrum. In the chiral limit we identify the emergence of a massless state in the pseudoscalar meson spectrum, i.e., the pion. We calculate all meson decay constants and confirm that the pion satisfies the Gell-Mann-Oakes relation in the light quark regime.Comment: 36 pages, 20 figure

On Exact Symmetries and Massless Vectors in Holographic Flows and other Flux Vacua

We analyze the isometries of Type IIB flux vacua based on the Papadopolous-Tseytlin ansatz and identify the related massless bulk vector fields. To this end we devise a general ansatz, valid in any flux compactification, for the fluctuations of the metric and p-forms that diagonalizes the coupled equations. We then illustrate the procedure in the simple case of holographic flows driven by the RR 3-form flux only. Specifically we study the fate of the isometries of the Maldacena-Nunez solution associated to wrapped D5-branes.Comment: 23 page

Managed care and patient ratings of the quality of specialty care among patients with pain or depressive symptoms

BACKGROUND: Managed care efforts to regulate access to specialists and reduce costs may lower quality of care. Few studies have examined whether managed care is associated with patient perceptions of the quality of care provided by physician and non-physician specialists. Aim is to determine whether associations exist between managed care controls and patient ratings of the quality of specialty care among primary care patients with pain and depressive symptoms who received specialty care for those conditions. METHODS: A prospective cohort study design was conducted in the offices of 261 primary physicians in private practice in Seattle in 1997. Patients (N = 17,187) were screened in waiting rooms, yielding a sample of 1,514 patients with pain only, 575 patients with depressive symptoms only, and 761 patients with pain and depressive symptoms. Patients (n = 1,995) completed a 6-month follow-up survey. Of these, 691 patients received specialty care for pain, and 356 patients saw mental health specialists. For each patient, managed care was measured by the intensity of managed care controls in the patient's health plan and primary care office. Quality of specialty care at follow-up was measured by patient rating of care provided by the specialists. Outcomes were pain interference and bothersomeness, Symptom Checklist for Depression, and restricted activity days. RESULTS: The intensity of managed care controls in health plans and primary care offices was generally not associated with patient ratings of the quality of specialty care. However, pain patients in more-managed primary care offices had lower ratings of the quality of specialty care from physician specialists and ancillary providers. CONCLUSION: For primary care patients with pain or depressive symptoms and who see specialists, managed care controls may influence ratings of specialty care for patients with pain but not patients with depressive symptoms

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Influence of organic molecules on the aggregation of TiO2 nanoparticles in acidic conditions

Engineered nanoparticles released into the environment may interact with natural organic matter (NOM). Surface complexation affects the surface potential, which in turn may lead to aggregation of the particles. Aggregation of synthetic TiO2 (anatase) nanoparticles in aqueous suspension was investigated at pH 2.8 as a function of time in the presence of various organic molecules and Suwannee River fulvic acid (SRFA), using dynamic light scattering (DLS) and high-resolution transmission electron microscopy (TEM). Results showed that the average hydrodynamic diameter and ?-potential were dependent on both concentration and molecular structure of the organic molecule. Results were also compared with those of quantitative batch adsorption experiments. Further, a time study of the aggregation of TiO2 nanoparticles in the presence of 2,3-dihydroxybenzoic acid (2,3-DHBA) and SRFA, respectively, was performed in order to observe changes in ?-potential and particle size over a time period of 9 months. In the 2,3-DHBA-TiO2 system, ?-potentials decreased with time resulting in charge neutralization and/or inversion depending on ligand concentration. Aggregate sizes increased initially to the micrometer size range, followed by disaggregation after several months. No or very little interaction between SRFA and TiO2 occurred at the lowest concentrations tested. However, at the higher concentrations of SRFA, there was an increase in both aggregate size and the amount of SRFA adsorbed to the TiO2 surface. This was in correlation with the ?-potential that decreased with increased SRFA concentration, leading to destabilization of the system. These results stress the importance of performing studies over both short and long time periods to better understand and predict the long-term effects of nanoparticles in the environment