Experimental moments of the nucleon structure function F2

Experimental data on the F2 structure functions of the proton and deuteron, including recent results from CLAS at Jefferson Lab, have been used to construct their n<=12 moments. A comprehensive analysis of the moments in terms of the operator product expansion has been performed to separate the moments into leading and higher twist contributions. Particular attention was paid to the issue of nuclear corrections in the deuteron, when extracting the neutron moments from data. The difference between the proton and neutron moments was compared directly with lattice QCD simulations. Combining leading twist moments of the neutron and proton we found the d/u ratio at x->1 approaching 0, although the precision of the data did not allow to exclude the 1/5 value. The higher twist components of the proton and neutron moments suggest that multi-parton correlations are isospin independent.Comment: Proceedings of 13th International QCD Conference (QCD 06), Montpellier, France, July 3-7th 200

Deuteron Compton Scattering in Effective Field Theory: Spin-Dependent Cross Sections and Asymmetries

Polarized Compton scattering on the deuteron is studied in nuclear effective field theory. A set of tensor structures is introduced to define 12 independent Compton amplitudes. The scalar and vector amplitudes are calculated up to ${\cal O}((Q/\Lambda)^2)$ in low-energy power counting. Significant contribution to the vector amplitudes is found to come from the spin-orbit type of relativistic corrections. A double-helicity dependent cross section $\Delta_1 \sigma = (\sigma_{+1-1}-\sigma_{+1+1})/2$ is calculated to the same order, and the effect of the nucleon isoscalar spin-dependent polarizabilities is found to be smaller than the effect of isoscalar spin-independent ones. Contributions of spin-independent polarizabilities are investigated in various asymmetries, one of which has as large as 12 (26) percent effect at the center-of-mass photon energy 30 (50) MeV.Comment: 22 pages, 8 figures included, replaced with the version submitted to PR

BB Potentials in Quenched Lattice QCD

The potentials between two B-mesons are computed in the heavy-quark limit using quenched lattice QCD at $m_\pi\sim 400~{\rm MeV}$. Non-zero central potentials are clearly evident in all four spin-isospin channels, (I,s_l) = (0,0) , (0,1) , (1,0) , (1,1), where s_l is the total spin of the light degrees of freedom. At short distance, we find repulsion in the $I\ne s_l$ channels and attraction in the I=s_l channels. Linear combinations of these potentials that have well-defined spin and isospin in the t-channel are found, in three of the four cases, to have substantially smaller uncertainties than the potentials defined with the s-channel (I,s_l), and allow quenching artifacts from single hairpin exchange to be isolated. The BB*\pi coupling extracted from the long-distance behavior of the finite-volume t-channel potential is found to be consistent with quenched calculations of the matrix element of the isovector axial-current. The tensor potentials in both of the s_l = 1 channels are found to be consistent with zero within calculational uncertainties.Comment: 30 page

Calculation of the heavy-hadron axial couplings g_1, g_2, and g_3 using lattice QCD

In a recent letter [Phys. Rev. Lett. 108, 172003 (2012), arXiv:1109.2480] we have reported on a lattice QCD calculation of the heavy-hadron axial couplings $g_1$, $g_2$, and $g_3$. These quantities are low-energy constants of heavy-hadron chiral perturbation theory (HH$\chi$PT) and are related to the $B^*B\pi$, $\Sigma_b^*\Sigma_b\pi$, and $\Sigma_b^{(*)}\Lambda_b\pi$ couplings. In the following, we discuss important details of the calculation and give further results. To determine the axial couplings, we explicitly match the matrix elements of the axial current in QCD with the corresponding matrix elements in HH$\chi$PT. We construct the ratios of correlation functions used to calculate the matrix elements in lattice QCD, and study the contributions from excited states. We present the complete numerical results and discuss the data analysis in depth. In particular, we demonstrate the convergence of $SU(4|2)$ HH$\chi$PT for the axial-current matrix elements at pion masses up to about 400 MeV and show the impact of the nonanalytic loop contributions. Finally, we present additional predictions for strong and radiative decay widths of charm and bottom baryons.Comment: 42 pages, 20 figures, updated calculation of Xi_b^{*0} width using mass measurement from CMS, published versio

Resonances in an external field: the 1+1 dimensional case

Using non-relativistic effective field theory in 1+1 dimensions, we generalize Luescher's approach for resonances in the presence of an external field. This generalized approach provides a framework to study the infinite-volume limit of the form factor of a resonance determined in lattice simulations.Comment: 13 pages, 2 postscript figure

Pion parton distribution functions from lattice QCD

We report on recent results for the pion matrix element of the twist-2 operator corresponding to the average momentum of non-singlet quark densities. For the first time finite volume effects of this matrix element are investigated and come out to be surprisingly large. We use standard Wilson and non-perturbatively improved clover actions in order to control better the extrapolation to the continuum limit. Moreover, we compute, fully non-perturbatively, the renormalization group invariant matrix element, which allows a comparison with experimental results in a broad range of energy scales. Finally, we discuss the remaining uncertainties, the extrapolation to the chiral limit and the quenched approximation.Comment: Lattice2003(matrix), 3 pages, 4 figure

Structure functions near the chiral limit

We compute hadron masses and the lowest moments of unpolarized and polarized nucleon structure functions down to pion masses of 300 MeV, in an effort to make unambiguous predictions at the physical light quark mass.Comment: 3 pages, 3 figures, Lattice2002(matrixel

Quark Mass Dependence of Nucleon Properties and Extrapolation from Lattice QCD

We summarize developments concerning the quark mass dependence of nucleon magnetic moments and the axial-vector coupling constant g_A. The aim is to explore the feasibility of chiral effective field theory methods for the extrapolation of lattice QCD results, from the relatively large quark masses that can be handled in such computations down to the physically relevant range.Comment: 9 pages, Latex, 4ps figures, uses World Scientific style file; presented at International School ``Quarks in Hadrons and Nuclei'', Erice, Sicily, September 200

On the modification of the Efimov spectrum in a finite cubic box

Three particles with large scattering length display a universal spectrum of three-body bound states called "Efimov trimers''. We calculate the modification of the Efimov trimers of three identical bosons in a finite cubic box and compute the dependence of their energies on the box size using effective field theory. Previous calculations for positive scattering length that were perturbative in the finite volume energy shift are extended to arbitrarily large shifts and negative scattering lengths. The renormalization of the effective field theory in the finite volume is explicitly verified. Moreover, we investigate the effects of partial wave mixing and study the behavior of shallow trimers near the dimer energy. Finally, we provide numerical evidence for universal scaling of the finite volume corrections.Comment: 21 pages, 8 figures, published versio