Spin structure of the nucleon at low energies

The spin structure of the nucleon is analyzed in the framework of a Lorentz-invariant formulation of baryon chiral perturbation theory. The structure functions of doubly virtual Compton scattering are calculated to one-loop accuracy (fourth order in the chiral expansion). We discuss the generalization of the Gerasimov-Drell-Hearn sum rule, the Burkhardt-Cottingham sum rule and moments of these. We give predictions for the forward and the longitudinal-transverse spin polarizabilities of the proton and the neutron at zero and finite photon virtuality. A detailed comparison to results obtained in heavy baryon chiral perturbation theory is also given.Comment: 29 pp, 14 fig

Nucleon Structure from Lattice QCD

Recent advances in lattice field theory, in computer technology and in chiral perturbation theory have enabled lattice QCD to emerge as a powerful quantitative tool in understanding hadron structure. I describe recent progress in the computation of the nucleon form factors and moments of parton distribution functions, before proceeding to describe lattice studies of the Generalized Parton Distributions (GPDs). In particular, I show how lattice studies of GPDs contribute to building a three-dimensional picture of the proton. I conclude by describing the prospects for studying the structure of resonances from lattice QCD.Comment: 6 pages, invited plenary talk at NSTAR 2007, 5-8 September 2007, Bonn, German

Generalized Parton Distributions from Hadronic Observables: Non-Zero Skewness

We propose a physically motivated parametrization for the unpolarized generalized parton distributions, H and E, valid at both zero and non-zero values of the skewness variable, \zeta. Our approach follows a previous detailed study of the \zeta=0 case where H and E were determined using constraints from simultaneous fits of the experimental data on both the nucleon elastic form factors and the deep inelastic structure functions in the non singlet sector. Additional constraints at \zeta \neq 0 are provided by lattice calculations of the higher moments of generalized parton distributions. We illustrate a method for extracting generalized parton distributions from lattice moments based on a reconstruction using sets of orthogonal polynomials. The inclusion in our fit of data on Deeply Virtual Compton Scattering is also discussed. Our method provides a step towards a model independent extraction of generalized distributions from the data. It also provides an alternative to double distributions based phenomenological models in that we are able to satisfy the polynomiality condition by construction, using a combination of experimental data and lattice, without resorting to any specific mathematical construct.Comment: 29 pages, 8 figures; added references, changed text in several place

Propionic fermentation by the probiotic Propionibacterium freudenreichii to functionalize whey

International audienceA new probiotic functionalized sweet whey was evaluated. Weaned healthy piglets consumed sweet whey (SW), unmodified or fermented by P. freudenreichii CIRM-BIA 129 (PF-SW). Fecal short chain fatty acids amounts remained unchanged. Bifidobacteria were enhanced in the PF-SW group, and so was the expression of T-bet, which orchestrates Th1 differentiation of T lymphocytes, in mesenteric lymph nodes immune cells (MLNC). This was consistent with ex vivo increased TNF-α secretion by MLNC in response to lipopolysaccharide (LPS). The consumption of the functionalized whey induced a different response in peripheral blood mononuclear cells (PBMC) to ex vivo stimulations, as the inhibition of TNF-α secretion in response to concanavalin A stimulation. Thus, by cultivating a probiotic GRAS bacterium in concentrated whey, prior to spray drying, it is possible to transform this by-product into a functional ingredient. This opens new avenues for the development of functional ingredients through enhanced valorisation of whey