Nucleon Structure in realistic QCD on a lattice

Arxiv preprint hep-lat/9308002, 1993

Physical Review D, 1996

We report on a high statistics quenched lattice QCD calculation of the deep-inelastic structure functions F 1 , F 2 , g 1 and g 2 of the proton and neutron. The theoretical basis for the calculation is the operator product expansion. We consider the moments of the leading twist operators up to spin four. Using Wilson fermions the calculation is done for three values of , and we perform the extrapolation to the chiral limit. The renormalization constants, which lead us from lattice to continuum operators, are calculated in perturbation theory to one loop order.

Nuclear Physics B - Proceedings Supplements, 2002

Using unimproved and non-perturbatively O(a) improved Wilson fermions, results are given for the three lowest moments of unpolarised nucleon structure functions. Renormalisation, chiral extrapolation and the continuum limit of the matrix elements are briefly discussed. The simulations are performed for both quenched and two flavours of unquenched fermions. No obvious sign of deviation from linearity in the chiral extrapolations are found. (This is most clearly seen in our quenched unimproved data, which extends to lighter quark mass.) Possible quenching effects also seem to be small. The lowest moment thus remains too large, so it seems to be necessary to reach smaller quark masses in numerical simulations.

1995

We describe a high statistics quenched QCD calculation of the moments of the polarized deep-inelastic structure functions g_1 and g_2 of the proton and neutron.

Nuclear Physics B - Proceedings Supplements, 1995

We h a v e initiated a programme to compute the lower moments of the unpolarised and polarised deep inelastic structure functions of the nucleon in the quenched approximation. We review our progress to date.

arXiv: High Energy Physics - Lattice, 2018

Precision experimental tests of the Standard Model of particle physics (SM) are one of our best hopes for discovering what new physics lies beyond the SM (BSM). Key in the search for new physics is the connection between theory and experiment. Forging this connection for searches involving low-energy hadronic or nuclear environments requires the use of a non-perturbative theoretical tool, lattice QCD. We present two recent lattice QCD calculations by the CalLat collaboration relevant for new physics searches: the nucleon axial coupling, $g_A$, whose precise value as predicted by the SM could help point to new physics contributions to the so-called "neutron lifetime puzzle", and hadronic matrix elements of short-ranged operators relevant for neutrinoless double beta decay searches.

Physical Review D, 2015

Nucleon-nucleon systems are studied with lattice quantum chromodynamics at a pion mass of m π ∼ 450 MeV in three spatial volumes using n f = 2 + 1 flavors of light quarks. At the quark masses employed in this work, the deuteron binding energy is calculated to be B d = 14.4 +3.2 −2.6 MeV, while the dineutron is bound by B nn = 12.5 +3.0 −5.0 MeV. Over the range of energies that are studied, the S-wave scattering phase shifts calculated in the 1 S 0 and 3 S 1-3 D 1 channels are found to be similar to those in nature, and indicate repulsive shortrange components of the interactions, consistent with phenomenological nucleon-nucleon interactions. In both channels, the phase shifts are determined at three energies that lie within the radius of convergence of the effective range expansion, allowing for constraints to be placed on the inverse scattering lengths and effective ranges. The extracted phase shifts allow for matching to nuclear effective field theories, from which low energy counterterms are extracted and issues of convergence are investigated. As part of the analysis, a detailed investigation of the single hadron sector is performed, enabling a precise determination of the violation of the Gell-Mann-Okubo mass relation.

2023

The current status of lattice-QCD numerical calculations by joint LHP, RBC, and UKQCD collaborations of nucleon isovector vector-and axialvector-current form factors using a 2+1-flavor dynamical domain-wall fermions lattice QCD ensemble generated jointly by RBC and UKQCD collaborations are presented. The lattice spacing is set at about 0.1141(3) fm, and the lattice spatial extent is 48 spacings or about 5.4750( ) fm. The strange and degenerate up and down quark mass values are set at their essentially physical values to provide the physical Ω mass and a degenerate pion mass of 0.1392(2) GeV. Our nucleon mass estimate is about 0.947(6) GeV. Possible excited-state contaminations in the calculated vector-and axialvector-current form factors are hidden below larger statistical noises. The numerical details of the form-factor shape parameters, such as the mean squared radii, the anomalous magnetic moment, or the pseudoscalar coupling extracted from the form factors, are described, along with comparisons of different approaches used to extract them.

Large NC QCD 2004, 2005

This talk describes progress at understanding the properties of the nucleon and its excitations from lattice QCD. I begin with a review of recent lattice results for the lowest-lying states of the excited baryon spectrum. The need to approach physical values of the light quark masses is emphasized, enabling the effects of the pion cloud to be revealed. I then outline the development of techniques that will enable the extraction of the masses of the higher resonances. I will describe how such calculations provide insight into the structure of the hadrons, and enable comparison both with experiment, and with QCD-inspired pictures of hadron structure, such as calculations in the limit of large Nc.