Lattice QCD Constraints on the Parton Distribution Functions of

The fraction of the longitudinal momentum of ^{3}He that is carried by the isovector combination of u and d quarks is determined using lattice QCD for the first time. The ratio of this combination to that in the constituent nucleons is found to be consistent with unity at the few-percent level from calculations with quark masses corresponding to m_{π}∼800 MeV. With a naive extrapolation to the physical quark masses, this constraint is consistent with, and more precise than, determinations from global nuclear parton distribution function fits through the nnnpdf framework. It is thus concretely demonstrated that lattice QCD calculations of light nuclei have imminent potential to enable more precise determinations of the u and d parton distributions in light nuclei and to reveal the QCD origins of the EMC effect.

Scalar, Axial, and Tensor Interactions of Light Nuclei from Lattice QCD.

Complete flavor decompositions of the matrix elements of the scalar, axial, and tensor currents in the proton, deuteron, diproton, and ^{3}He at SU(3)-symmetric values of the quark masses corresponding to a pion mass m_{π}∼806 MeV are determined using lattice quantum chromodynamics. At the physical quark masses, the scalar interactions constrain mean-field models of nuclei and the low-energy interactions of nuclei with potential dark matter candidates. The axial and tensor interactions of nuclei constrain their spin content, integrated transversity, and the quark contributions to their electric dipole moments. External fields are used to directly access the quark-line connected matrix elements of quark bilinear operators, and a combination of stochastic estimation techniques is used to determine the disconnected sea-quark contributions. The calculated matrix elements differ from, and are typically smaller than, naive single-nucleon estimates. Given the particularly large, O(10%), size of nuclear effects in the scalar matrix elements, contributions from correlated multinucleon effects should be quantified in the analysis of dark matter direct-detection experiments using nuclear targets.

Proton-Proton Fusion and Tritium ß Decay from Lattice Quantum Chromodynamics.

The nuclear matrix element determining the pp→de^{+}ν fusion cross section and the Gamow-Teller matrix element contributing to tritium ß decay are calculated with lattice quantum chromodynamics for the first time. Using a new implementation of the background field method, these quantities are calculated at the SU(3) flavor-symmetric value of the quark masses, corresponding to a pion mass of m_{π}∼806 MeV. The Gamow-Teller matrix element in tritium is found to be 0.979(03)(10) at these quark masses, which is within 2σ of the experimental value. Assuming that the short-distance correlated two-nucleon contributions to the matrix element (meson-exchange currents) depend only mildly on the quark masses, as seen for the analogous magnetic interactions, the calculated pp→de^{+}ν transition matrix element leads to a fusion cross section at the physical quark masses that is consistent with its currently accepted value. Moreover, the leading two-nucleon axial counterterm of pionless effective field theory is determined to be L_{1,A}=3.9(0.2)(1.0)(0.4)(0.9) fm^{3} at a renormalization scale set by the physical pion mass, also agreeing within the accepted phenomenological range. This work concretely demonstrates that weak transition amplitudes in few-nucleon systems can be studied directly from the fundamental quark and gluon degrees of freedom and opens the way for subsequent investigations of many important quantities in nuclear physics.

Isotensor Axial Polarizability and Lattice QCD Input for Nuclear Double-ß Decay Phenomenology.

The potential importance of short-distance nuclear effects in double-ß decay is assessed using a lattice QCD calculation of the nn→pp transition and effective field theory methods. At the unphysical quark masses used in the numerical computation, these effects, encoded in the isotensor axial polarizability, are found to be of similar magnitude to the nuclear modification of the single axial current, which phenomenologically is the quenching of the axial charge used in nuclear many-body calculations. This finding suggests that nuclear models for neutrinoful and neutrinoless double-ß decays should incorporate this previously neglected contribution if they are to provide reliable guidance for next-generation neutrinoless double-ß decay searches. The prospects of constraining the isotensor axial polarizabilities of nuclei using lattice QCD input into nuclear many-body calculations are discussed.

The effect of Arthrospira platensis capsules on CD4 T-cells and antioxidative capacity in a randomized pilot study of adult women infected with human immunodeficiency virus not under HAART in Yaoundé, Cameroon.

Dietary supplements are often used to improve the nutritional status of people living with HIV/AIDS (PLHIV). Arthrospira platensis (Asp), also known as Spirulina, is a cyanobacterium rich in proteins and micronutrients. Cell and animal trials described immune-modulating, antiretroviral and antioxidant activities. This pilot study describes the effects of the supplementation of 5 g/day of Asp on a pre-highly-active antiretroviral therapy (pre-HAART), HIV-infected, adult female population. It was conducted as a three-month randomized controlled trial (RCT) that compared a cup supplementation of five grams/day of Asp with a placebo of equal protein content and energy. The study included 73 HIV-infected women. The immediate outcome variables were CD4 T-cells, viral load and immune activation by CD8 T-cells expressing CD38. The antioxidant status was assessed by way of the total antioxidant capacity of the serum (TAOS). The renal function was documented by way of creatinine, urea and the calculated glomerular filtration rate. Statistical analyses were carried out with non-parametric tests, and the effect size of each interaction was calculated. No differences in the immunological and virological markers between the Asp and the placebo group could be observed. In the placebo group, 21 of 30 patients (70%) developed concomitant events, while in the Asp group, only 12 of 28 patients (43%) did. Both groups registered a significant weight increase; 0.5 kg (p < 0.05) in the Asp group and 0.65 kg (p < 0.05) in the placebo group. The antioxidant capacity increase of 56 (1-98) µM for Asp was significantly different from the decrease observed in the placebo group (p < 0.001). A slight increase in the creatinine level of 0.1 g/dL (p < 0.001) was observed in the Asp group, and no effect was observed in the urea levels. The improvement of the antioxidant capacity under Asp, shown for the first time on PLHIV, could become a focus for future research on the nutritional and health effects of Spirulina. The observed slight, but significant increase of serum creatinine needs further evaluation, especially with varying doses of Asp.

Geometric properties of the three-dimensional Ising and XY models.

The fractal structure of high-temperature graphs of the three-dimensional Ising and XY models is investigated by simulating these graphs directly on a cubic lattice and analyzing them with the help of percolation observables. The Ising graphs are shown to percolate right at the Curie critical point. The diverging length scale relevant to the graphs in the vicinity of the percolation threshold is shown to be provided by the spin correlation length. The fractal dimension of the high-temperature graphs at criticality is estimated to be D=1.7349(65) for the Ising and D=1.7626(66) for the XY models.