Kinetic Equations for Longwavelength Excitations of the Quark-Gluon Plasma

We show that longwavelength excitations of the quark-gluon plasma are described by simple kinetic equations which represent the exact equations of motion at leading order in $g$. Properties of the so-called ``hard thermal loops'', i.e. the dominant contributions to amplitudes with soft external lines, find in this approach a natural explanation. In particular, their generating functional appears here as the effective action describing long wavelength excitations of the plasma.Comment: January 8, 1993; 8 pages; SPhT/93-

Lifetime of quasiparticles in hot QED plasmas

The calculation of the lifetime of quasiparticles in a QED plasma at high temperature remains plagued with infrared divergences, even after one has taken into account the screening corrections. The physical processes responsible for these divergences are the collisions involving the exchange of very soft, unscreened, magnetic photons, whose contribution is enhanced by the thermal Bose-Einstein occupation factor. The self energy diagrams which diverge in perturbation theory contain no internal fermion loops, but an arbitrary number of internal magnetostatic photon lines. By generalizing the Bloch-Nordsieck model at finite temperature, we can resum all the singular contributions of such diagrams, and obtain the correct long time behaviour of the retarded fermion propagator in the hot QED plasma: $S_R(t)\sim \exp\{-\alpha T \, t\, \ln\omega_pt\}$, where $\omega_p=eT/3$ is the plasma frequency and $\alpha=e^2/4\pi$.Comment: 13 pages, LaTe

Non-Abelian Excitations of the Quark-Gluon Plasma

We present new, non-abelian, solutions to the equations of motion which describe the collective excitations of a quark-gluon plasma at high temperature. These solutions correspond to spatially uniform color oscillations.Comment: 8 pages LaTex, 1 figure (not included; available upon request), Saclay preprint T94/0

Differential Cross Sections for Higgs Boson Production at Tevatron Collider Energies

The transverse momentum $Q_T$ distribution is computed for inclusive Higgs boson production at $\sqrt{S} = 1.96$ TeV. We include all-orders resummation of large logarithms associated with emission of soft gluons at small $Q_T$. We provide results for Higgs boson and $Z^*$ masses from $M_Z$ to 200 GeV. The relatively hard transverse momentum distribution for Higgs boson production suggests possibilities for improvement of the signal to background ratio.Comment: 12 pages, latex, 7 figure

Superconducting instability in 3 band metallic nanotubes

Motivated by recent experiments on small radius nanotubes, we study the superconducting instabilities of cylindrical (5,0) nanotubes. According to band structure calculations, thesenanotubes possess three bands at the Fermi energy. Using a fermionic renormalization group approach and a careful bosonization treatment,we consider the effect of different attractive interactions, mediated by phonons, within the Luttinger Liquid framework. We particularly focus on a superconducting instability specific to the three bands model we consider for the description of these (5,0) cylindrical nanotubes.Comment: RevTeX 4, 17 pages, 10 EPS figure

Statics and dynamics of weakly coupled antiferromagnetic spin-1/2 ladders in a magnetic field

We investigate weakly coupled spin-1/2 ladders in a magnetic field. The work is motivated by recent experiments on the compound (C5H12N)2CuBr4 (BPCB). We use a combination of numerical and analytical methods, in particular the density matrix renormalization group (DMRG) technique, to explore the phase diagram and the excitation spectra of such a system. We give detailed results on the temperature dependence of the magnetization and the specific heat, and the magnetic field dependence of the nuclear magnetic resonance (NMR) relaxation rate of single ladders. For coupled ladders, treating the weak interladder coupling within a mean-field or quantum Monte Carlo approach, we compute the transition temperature of triplet condensation and its corresponding antiferromagnetic order parameter. Existing experimental measurements are discussed and compared to our theoretical results. Furthermore we compute, using time dependent DMRG, the dynamical correlations of a single spin ladder. Our results allow to directly describe the inelastic neutron scattering cross section up to high energies. We focus on the evolution of the spectra with the magnetic field and compare their behavior for different couplings. The characteristic features of the spectra are interpreted using different analytical approaches such as the mapping onto a spin chain, a Luttinger liquid (LL) or onto a t-J model. For values of parameters for which such measurements exist, we compare our results to inelastic neutron scattering experiments on the compound BPCB and find excellent agreement. We make additional predictions for the high energy part of the spectrum that are potentially testable in future experiments.Comment: 35 pages, 26 figure

Impact of Appropriate Antimicrobial Therapy for Patients with Severe Sepsis and Septic Shock – A Quality Improvement Study

Background There is ample literature available on the association between both time to antibiotics and appropriateness of antibiotics and clinical outcomes from sepsis. In fact, the current state of debate surrounds the balance to be struck between prompt empirical therapy and care in the choice of appropriate antibiotics (both in terms of the susceptibility of infecting organism and minimizing resistance arising from use of broad-spectrum agents). The objective of this study is to determine sepsis bundle compliance and the appropriateness of antimicrobial therapy in patients with severe sepsis and septic shock and its impact on outcomes. Material This study was conducted in the ICU of a tertiary care, private hospital in São Paulo, Brazil. A retrospective cohort study was conducted from July 2005 to December 2012 in patients with severe sepsis and septic shock. Results A total of 1,279 patients were identified with severe sepsis and septic shock, of which 358 (32.1%) had bloodstream infection (BSI). The inpatient mortality rate was 29%. In evaluation of the sepsis bundle, over time there was a progressive increase in serum arterial lactate collection, obtaining blood cultures prior to antibiotic administration, administration of broad-spectrum antibiotics within 1 hour, and administration of appropriate antimicrobials, with statistically significant differences in the later years of the study. We also observed a significant decrease in mortality. In patients with bloodstream infection, after adjustment for other covariates the administration of appropriate antimicrobial therapy was associated with a decrease in mortality in patients with severe sepsis and septic shock (p = 0.023). Conclusions The administration of appropriate antimicrobial therapy was independently associated with a decline in mortality in patients with severe sepsis and septic shock due to bloodstream infection. As protocol adherence increased over time, the crude mortality rate decreased, which reinforces the need to implement institutional guidelines and monitor appropriate antimicrobial therapy compliance

Lifetimes of quasiparticles and collective excitations in hot QED plasmas

The perturbative calculation of the lifetime of fermion excitations in a QED plasma at high temperature is plagued with infrared divergences which are not eliminated by the screening corrections. The physical processes responsible for these divergences are the collisions involving the exchange of longwavelength, quasistatic, magnetic photons, which are not screened by plasma effects. The leading divergences can be resummed in a non-perturbative treatement based on a generalization of the Bloch-Nordsieck model at finite temperature. The resulting expression of the fermion propagator is free of infrared problems, and exhibits a {\it non-exponential} damping at large times: $S_R(t)\sim \exp\{-\alpha T t \ln\omega_pt\}$, where $\omega_p=eT/3$ is the plasma frequency and $\alpha=e^2/4\pi$.Comment: LaTex file, 57 pages, 11 eps figures include

Galaxy Zoo: Are Bars Responsible for the Feeding of Active Galactic Nuclei at 0.2 < z < 1.0?

We present a new study investigating whether active galactic nuclei (AGN) beyond the local universe are preferentially fed via large-scale bars. Our investigation combines data from Chandra and Galaxy Zoo: Hubble (GZH) in the AEGIS, COSMOS, and GOODS-S surveys to create samples of face-on, disc galaxies at 0.2 < z < 1.0. We use a novel method to robustly compare a sample of 120 AGN host galaxies, defined to have 10^42 erg/s < L_X < 10^44 erg/s, with inactive control galaxies matched in stellar mass, rest-frame colour, size, Sersic index, and redshift. Using the GZH bar classifications of each sample, we demonstrate that AGN hosts show no statistically significant enhancement in bar fraction or average bar likelihood compared to closely-matched inactive galaxies. In detail, we find that the AGN bar fraction cannot be enhanced above the control bar fraction by more than a factor of two, at 99.7% confidence. We similarly find no significant difference in the AGN fraction among barred and non-barred galaxies. Thus we find no compelling evidence that large-scale bars directly fuel AGN at 0.2<z<1.0. This result, coupled with previous results at z=0, implies that moderate-luminosity AGN have not been preferentially fed by large-scale bars since z=1. Furthermore, given the low bar fractions at z>1, our findings suggest that large-scale bars have likely never directly been a dominant fueling mechanism for supermassive black hole growth.Comment: 13 pages, 5 figures, 2 tables, accepted by MNRA