Yoctosecond photon pulses from quark-gluon plasmas

Present ultra-fast laser optics is at the frontier between atto- and zeptosecond photon pulses, giving rise to unprecedented applications. We show that high-energetic photon pulses down to the yoctosecond timescale can be produced in heavy ion collisions. We focus on photons produced during the initial phase of the expanding quark-gluon plasma. We study how the time evolution and properties of the plasma may influence the duration and shape of the photon pulse. Prospects for achieving double peak structures suitable for pump-probe experiments at the yoctosecond timescale are discussed.Comment: 4 pages, 2 figures; final version as accepted by PR

Streaking At High Energies With Electrons And Positrons

State-of-the-art attosecond metrology deals with the detection and characterization of photon pulses with typical energies up to the hundreds of eV and time resolution of several tens of attoseconds. Such short pulses are used for example to control the motion of electrons on the atomic scale or to measure inner-shell atomic dynamics. The next challenge of time-resolving the inner-nuclear dynamics, transient meson states and resonances requires photon pulses below attosecond duration and with energies exceeding the MeV scale. Here we discuss a detection scheme for time-resolving high-energy gamma ray pulses down to the zeptosecond timescale. The scheme is based on the concept of attosecond streak imaging, but instead of conversion of photons into electrons in a nonlinear medium, the high-energy process of electron-positron pair creation is utilized. These pairs are produced in vacuum through the collision of a test pulse to be characterized with an intense laser pulse, and they acquire additional energy and momentum depending on their phase in the streaking pulse at the moment of production. A coincidence measurement of the electron and positron momenta after the interaction provides information on the pair production phase within the streaking pulse. We examine the limitations imposed by quantum radiation reaction in multiphoton Compton scattering on this detection scheme, and discuss other necessary conditions to render the scheme feasible in the upcoming Extreme Light Infrastructure (ELI) laser facility.Comment: 6 pages, 2 figures, contribution to the AIP proceedings of "Light at Extreme Intensities" (LEI 2011), Szeged, Hungary, Nov 14-18, 201

Anomalous specific heat in high-density QED and QCD

Long-range quasi-static gauge-boson interactions lead to anomalous (non-Fermi-liquid) behavior of the specific heat in the low-temperature limit of an electron or quark gas with a leading $T\ln T^{-1}$ term. We obtain perturbative results beyond the leading log approximation and find that dynamical screening gives rise to a low-temperature series involving also anomalous fractional powers $T^{(3+2n)/3}$. We determine their coefficients in perturbation theory up to and including order $T^{7/3}$ and compare with exact numerical results obtained in the large-$N_f$ limit of QED and QCD.Comment: REVTEX4, 6 pages, 2 figures; v2: minor improvements, references added; v3: factor of 2 error in the T^(7/3) coefficient corrected and plots update

The use of the full blood count and differential parameters to assess immune activation levels in asymptomatic, untreated HIV infection

CITATION: Vanker, N. & Ipp, H. 2014. The use of the full blood count and differential parameters to assess immune activation levels in asymptomatic, untreated HIV infection. South African Medical Journal, 104(1), doi::10.7916/SAMJ.6983.The original publication is available at http://www.samj.org.zaBackground. A feature of HIV/AIDS is chronic immune activation, which results in a number of complications including inflammation-related disorders and blood cytopaenias. Immune activation status is not routinely tested in HIV infection. However, the full blood count (FBC) is a commonly performed test. Objective. We hypothesised that FBC parameters would be significantly different in HIV-infected v. -uninfected individuals, and that some of these parameters would correlate with markers of immune activation (i.e. percentage CD38 expression on CD8+ T cells (%CD38onCD8)) and disease progression (i.e. CD4+ counts) in HIV infection. Methods. This was a cross-sectional study with 83 HIV-infected adults who were antiretroviral therapy-naive and clinically well, and 51 HIV-uninfected adults. The %CD38onCD8 and CD4+ counts were determined by flow cytometry and the FBC was performed on a Siemens ADVIA 2120 system. FBC parameters investigated were total white cell count (WCC), haemoglobin (Hb) concentration, platelet count, absolute neutrophil count, absolute lymphocyte count, and percentage of large unstained cells (%LUCs). Results. Significant differences were found between the HIV-infected and -uninfected groups for total WCC, Hb, neutrophil count, lymphocyte count and %LUCs. The mean ± standard deviation (SD) for the total WCC (5.3±1.3 v. 6.9±2.2; p≤0.001) and the %LUCs (2.5±0.9 v. 2.0±0.9; p=0.001) both showed correlations with CD4+ counts and %CD38onCD8. Conclusion. The total WCC and %LUCs showed significant differences in HIV-infected individuals and correlated with markers of immune activation and disease progression. This suggests the potential use of these parameters as markers of immune activation in HIV infection.http://www.samj.org.za/index.php/samj/article/view/12355Publisher's versio

The use of the full blood count and differential parameters to assess immune activation levels in asymptomatic, untreated HIV infection

  Background. A feature of HIV/AIDS is chronic immune activation, which results in a number of complications including inflammation-related disorders and blood cytopaenias. Immune activation status is not routinely tested in HIV infection. However, the full blood count (FBC) is a commonly performed test. Objective. We hypothesised that FBC parameters would be significantly different in HIV-infected v. -uninfected individuals, and that some of these parameters would correlate with markers of immune activation (i.e. percentage CD38 expression on CD8+ T cells (%CD38onCD8)) and disease progression (i.e. CD4+ counts) in HIV infection. Methods. This was a cross-sectional study with 83 HIV-infected adults who were antiretroviral therapy-naive and clinically well, and 51 HIV-uninfected adults. The %CD38onCD8 and CD4+ counts were determined by flow cytometry and the FBC was performed on a Siemens ADVIA 2120 system. FBC parameters investigated were total white cell count (WCC), haemoglobin (Hb) concentration, platelet count, absolute neutrophil count, absolute lymphocyte count, and percentage of large unstained cells (%LUCs). Results. Significant differences were found between the HIV-infected and -uninfected groups for total WCC, Hb, neutrophil count, lymphocyte count and %LUCs. The mean ± standard deviation (SD) for the total WCC (5.3±1.3 v. 6.9±2.2; p≤0.001) and the %LUCs (2.5±0.9 v. 2.0±0.9; p=0.001) both showed correlations with CD4+ counts and %CD38onCD8. Conclusion. The total WCC and %LUCs showed significant differences in HIV-infected individuals and correlated with markers of immune activation and disease progression. This suggests the potential use of these parameters as markers of immune activation in HIV infection.

Ultra-strong laser pulses: streak-camera for gamma-rays via pair production and quantum radiative reaction

We show that a strong laser pulse combined with a strong x-ray pulse can be employed in a detection scheme for characterizing high-energy $\gamma$-ray pulses down to the zeptosecond timescale. The scheme employs streak imaging technique built upon the high-energy process of electron-positron pair production in vacuum through the collision of a test pulse with intense laser pulses. The role of quantum radiation reaction in multiphoton Compton scattering process and limitations imposed by it on the detection scheme are examined

Modulation of LPS-Induced CD4+ T-Cell Activation and Apoptosis by Antioxidants in Untreated Asymptomatic HIV Infected Participants: An In Vitro Study

Persistent immune activation characterises HIV infection and is associated with depletion of CD4+ T-cells and increased risk of disease progression. Early loss of gut mucosal integrity results in the translocation of microbial products such as lipopolysaccharide (LPS) into the systemic circulation. This is an important source of on-going immune stimulation. The purpose of this study was to determine levels of CD4+ T-cell activation (%CD25 expression) and apoptosis (% annexin V/7-AAD) in asymptomatic, untreated HIV infection at baseline and after stimulation with LPS and incubation with or without vitamin C and N-acetylcysteine. LPS induced a significant ( < 0.03) increase in %CD25 expression, annexin V, and 7-AAD in HIV positive individuals. NAC in combination with vitamin C, significantly ( = 0.0018) reduced activation and early apoptosis of CD4+ T-cells to a greater degree than with either antioxidant alone. Certain combinations of antioxidants could be important in reducing the harmful effects of chronic immune activation and thereby limit CD4+ T-cell depletion. Importantly, we showed that CD4+ T-cells of the HIV positive group responded better to a combination of the antioxidants at this stage than those of the controls. Therefore, appropriate intervention at this asymptomatic stage could rescue the cells before repetitive activation results in the death of CD4+ T-cells

Advances in perturbative thermal field theory

The progress of the last decade in perturbative quantum field theory at high temperature and density made possible by the use of effective field theories and hard-thermal/dense-loop resummations in ultrarelativistic gauge theories is reviewed. The relevant methods are discussed in field theoretical models from simple scalar theories to non-Abelian gauge theories including gravity. In the simpler models, the aim is to give a pedagogical account of some of the relevant problems and their resolution, while in the more complicated but also more interesting models such as quantum chromodynamics, a summary of the results obtained so far are given together with references to a few most recent developments and open problems.Comment: 84 pages, 18 figues, review article submitted to Reports on Progress in Physics; v2, v3: minor additions and corrections, more reference

Two-loop HTL Thermodynamics with Quarks

We calculate the quark contribution to the free energy of a hot quark-gluon plasma to two-loop order using hard-thermal-loop (HTL) perturbation theory. All ultraviolet divergences can be absorbed into renormalizations of the vacuum energy and the HTL quark and gluon mass parameters. The quark and gluon HTL mass parameters are determined self-consistently by a variational prescription. Combining the quark contribution with the two-loop HTL perturbation theory free energy for pure-glue we obtain the total two-loop QCD free energy. Comparisons are made with lattice estimates of the free energy for N_f=2 and with exact numerical results obtained in the large-N_f limit.Comment: 33 pages, 6 figure