Etude de la structure du nucléon par des calculs de QCD sur réseau avec des fermions de masse twistée

Abstract : Understanding the structure of the nucleon from Quantum ChromoDynamics is one of the greatest challenges of hadronic physics. Only lattice QCD allows to determine numerically the values of the observables from ab-initio principles. This thesis aims to study the nucleon form factors and the first moments of partons distribution fnctions by using a discretized action with twisted mass fermions. As a main advantage, the discretization effects are suppressed at first order in the lattice spacing. In addition, the set of simulations allows a good control of the systematical errors. After reviewing the computation technics, the results obtained for a wide range of parameters are presented, with lattice spacings varying from 0.0056 fm to 0.089 fm, spatial volumes from 2.1 up to 2.7 fm and several pion masses in the range of 260-470 MeV. The vector renormalization constant was determined in the nucleon sector with improved precision. Concerning the electric charge radius, we found a finite volume effect that provides a key towards an explanation of the chiral dependence to the physical point. The results for the magnetic moment, the axila charge, the magnetic and axial charge radii, the momentum and spin fractions carried by the quarks show no dependence on the lattice spacing nor volume. In our range of pion masses, their values show a deviationfrom the experimental values. Their chiral behaviour do not exhibit the curvature predicted by the chiral perturbation theory which could explain the apparent discrepancy.
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Submitted on : Tuesday, December 14, 2010 - 12:57:27 PM
Last modification on : Tuesday, May 22, 2018 - 9:48:06 PM
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Pierre-Antoine Harraud. Etude de la structure du nucléon par des calculs de QCD sur réseau avec des fermions de masse twistée. Physique des Hautes Energies - Expérience [hep-ex]. Université Joseph-Fourier - Grenoble I, 2010. Français. ⟨NNT : LPSC10169⟩. ⟨tel-00546526⟩

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