Transverse single spin asymmetry in elastic electron-proton scattering

We discuss the two-photon exchange contribution to observables which involve lepton helicity flip in elastic lepton-nucleon scattering. This contribution is accessed through the single spin asymmetry for a lepton beam polarized normal to the scattering plane. We estimate this beam normal spin asymmetry at large momentum transfer using a parton model and we express the corresponding amplitude in terms of generalized parton distributions

Renormalization of quark propagator, vertex functions and twist-2 operators from twisted-mass lattice QCD at NfN_f=4

We present a precise non-perturbative determination of the renormalization constants in the mass independent RI'-MOM scheme. The lattice implementation uses the Iwasaki gauge action and four degenerate dynamical twisted mass fermions. The gauge configurations are provided by the ETM Collaboration. Renormalization constants for scalar, pseudo-scalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two volumes and several twisted mass parameters. The method we developed allows for a precise cross-check of the running, thanks to the particular proper treatment of hypercubic artifacts. Results for the twist-2 operator $O_{44}$ are also presented.Comment: 20 pages, 20 figures, submitted to Phys. Rev.

Renormalization constants for Nf=2+1+1N_{\rm f}=2+1+1 twisted mass QCD

We summarize recent non-perturbative results obtained for the renormalization constants computed in the RI'-MOM scheme for $N_{\rm f}=2+1+1$ twisted mass QCD. Our implementation employs the Iwasaki gauge action and four dynamical degenerate twisted mass fermions. Renormalization constants for scalar, pseudo-scalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two different volumes and several values of the twisted mass. Our method allows for a precise cross-check of the running, because of the particular proper treatment of the hypercubic artifacts. Preliminary results for twist-2 operators are also presented

The Recoil Proton Polarization: a new discriminative DVCS observable

Generalized parton distributions describe the correlations between the longitudinal momentum and the transverse position of quarks and gluons in a nucleon. They can be constrained by measuring photon leptoproduction observables, arising from the interference between Bethe-Heitler and Deeply virtual Compton scattering processes. At leading-twist/leading-order, the amplitude of the latter is parameterized by complex integrals of the GPDs {H, E, \~H, \~E} . As data collected on an unpolarized or longitudinally polarized target constrains H and \~H, E is poorly known as it requires data collected with a transversely polarized target, which is very challenging to implement in fixed target experiments. The only alternative considered so far has been DVCS on a neutron with a deuterium target, while assuming isospin symmetry and absence of final-state interactions. Today, we introduce the polarization of the recoil proton as a new DVCS observable, highly sensitive to E, which appears feasible for an experimental study at a high-luminosity facility such as Jefferson Lab

Excluded Volume Effects on Cold Neutron Star Phenomenology

Observable properties of neutron stars are studied within a hadronic equation of state derived from the quark level. The effect of short-range repulsion is incorporated within the excluded volume framework. It is found that one can sustain neutron stars with masses as large as 2.2$M_\odot$ even including hyperons in $\beta$ equilibrium, while producing radii and tidal deformabilities consistent with current constraints

Baryon masses with dynamical twisted mass fermions

We present results on the mass of the nucleon and the $\Delta$ using two dynamical degenerate twisted mass quarks. The evaluation is performed at four quark masses corresponding to a pion mass in the range of 690-300 MeV on lattices of size 2.1 fm and 2.7 fm. We check for cutoff effects by evaluating these baryon masses on lattices of spatial size 2.1 fm with lattice spacings $a(\beta=3.9)=0.0855(6)$ fm and $a(\beta=4.05)=0.0666(6)$ fm, determined from the pion sector and find them to be within our statistical errors. Lattice results are extrapolated to the physical limit using continuum chiral perturbation theory. The nucleon mass at the physical point provides a determination of the lattice spacing. Using heavy baryon chiral perturbation theory at ${\cal O}(p^3)$ we find $a(\beta=3.9)=0.0879(12)$ fm, with a systematic error due to the chiral extrapolation estimated to be about the same as the statistical error. This value of the lattice spacing is in good agreement with the value determined from the pion sector. We check for isospin breaking in the $\Delta$-system. We find that $\Delta^{++,-}$ and $\Delta^{+,0}$ are almost degenerate pointing to small flavor violating effects.Comment: 7 pages, 9 figures. Talk presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

The role of nucleon structure in finite nuclei

The quark-meson coupling model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of $\sigma$, $\omega$ and $\rho$ mesons, is extended to investigate the properties of finite nuclei. Using the Born-Oppenheimer approximation to describe the interacting quark-meson system, we derive the effective equation of motion for the nucleon, as well as the self-consistent equations for the meson mean fields. The model is first applied to nuclear matter, after which we show some initial results for finite nuclei.Comment: The revised version. This is tar, compressed and uuencoded (including 3 tables and 8 figures). 45 page

Superheavy Nuclei in the Quark-Meson-Coupling Model

We present a selection of the first results obtained in a comprehensive calculation of ground state properties of even-even superheavy nuclei in the region of 96 < Z < 136 and 118 < N < 320 from the Quark-Meson-Coupling model (QMC). Ground state binding energies, the neutron and proton number dependence of quadrupole deformations and Qα values are reported for even-even nuclei with 100 < Z < 136 and compared with available experimental data and predictions of macro-microscopic models. Predictions of properties of nuclei, including Qα values, relevant for planning future experiments are presented

Superheavy Nuclei in the Quark-Meson-Coupling Model

We present a selection of the first results obtained in a comprehensive calculation of ground state properties of even-even superheavy nuclei in the region of 96 < Z < 136 and 118 < N < 320 from the Quark-Meson-Coupling model (QMC). Ground state binding energies, the neutron and proton number dependence of quadrupole deformations and Qα values are reported for even-even nuclei with 100 < Z < 136 and compared with available experimental data and predictions of macro-microscopic models. Predictions of properties of nuclei, including Qα values, relevant for planning future experiments are presented

Chromodynamique quantique sur réseau et propriétés du nucléon

L objet de cette thèse est le calcul ab-initio des propriétés du nucléon en partant de la théorie microscopique de l interaction forte, la chromodynamique antique (QCD). Celle-ci est discrétisée sur un réseau quadridimensionnel et les observables quantiques sont calculées par la méthode de l intégrale de chemin, comme expliqué dans les chapitres II et III. Dans le chapitre IV nous discutons les problèmes posés par la discrétisation des fermions et nous expliquons le choix retenu par nos calculs c est-à-dire la discrétisation à la Wilson avec masse twistée.Le calcul numérique de l intégrale de chemin est fait par la méthode de Monte Carlo avec échantillonnage préférentiel. L algorythme Hybrid Monte Carlo , basé sur la dynamique moléculaire, est présenté dans le chapitre V ainsi que la méthode de résolution de grands systèmes linéaires creux qui apparaissent dans le calcul des observables. Ce chapitre présente aussi les aspects informatiques du problème, c est-à-dire le parallélisme massif ainsi que les caractéristiques des machines utilisées. Dans le chapitre VI nous expliquons la méthodologie suivie pour pour la production des ensembles représentatifs de configuration de jauge. La mise en œuvre et le contrôle de cette production est une part importante du travail effectué pendant cette thèse. Les deux derniers chapitres sont consacrés au calcul proprement dit des observables et à la présentation des résultats. Dans la conclusion nous faisons le point des calculs de QCD sur réseau et nous discutons de l évolution du domaine dans la perspective des nouveaux moyens de calculs et des développements théoriques récents.The goal of this thesis is to compute from first principles nucleon properties, starting from the microscopic theory of strong interaction, quantum chromodynamics (QCD). It uses a four-dimensional lattice on which theory is discretized and quantum observables are computed through path integral techniques, as explained in chapters II and III. In chapter IV we discuss problems faced when fermions are taken into account and we present the choice for our computations ie a discretization à la Wilson plus an additional twisted mass. The numerical evaluation of path integrals is done by Monte Carlo methods with importance sampling. The Hybrid Monte Carlo algorithm, based on molecular dynamics, is presented in chapter V together with a method to solve large sparse linear systems necessary to compute observables. This chapter also describes computer science details of the problem which are the use of massive parallel processing and some characteristics of computers used. In chapter VI we explain how the production of representative samples of gauge configuration is performed. This step and its control is an important part of the work done during this thesis. The last two chapters are devoted to the computation of observables and to the presentation of results. The main technical difficulty which is to solve for quark propagators has been performed by using available processor farms at their best. A good part of this work has been focused on this. To conclude we comment on the status of the calculations and we discuss the evolution of the field in the perspective of new computing facilities and recent theoretical progress.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF