Nucleon electromagnetic form factors from lattice QCD

Abstract

It is imperative that lattice QCD serve to develop our understanding of hadron structure and, where possible, to guide the interpretation of experimental data. There is now a great deal of effort directed at the calculation of the electroweak form factors of the nucleon, where for example, measurements at Jefferson Laboratory have recently revealed surprising behaviour in the ratio GE/GM . While, for the present, calculations within the framework of lattice QCD are limited to relatively large quark mass, there has been considerable progress in our understanding of how to extrapolate to the chiral limit. Here we report the results of the application of these techniques to the most recent form factor data from the QCDSF Collaboration. The level of agreement with all of the form factors, for Q 2 below 1 GeV 2 , is already impressive.

Comparison of nucleon form factors from lattice QCD against the light front cloudy bag model and extrapolation to the physical mass regime

“…The resulting plots for G E , G M and their ratios vs Q 2 for both proton and neutron are shown in Figs. [15][16][17][18][19][20]. Figure 17 shows that our results are in more or less good agreement with the experimental data in the low-Q 2 region, but yield a slightly lower value of Q 2 for the zero crossover point than that extrapolated from experiment [30].…”

“…The factor γ determines the size of the momenta appearing in the integrands of Eqs. (17) and (18). The corresponding integrands differ by terms that are ratios of second order polynomials of the integration variables.…”

On Nucleon Electromagnetic Form Factors

“…Since regularisation-parameter-dependent parts of the chiral loops are important we follow Ref. [73] and estimate the corrections using modified formulae that incorporate a single parameter which mimics the effect of regularising the integrals. Thus Eqs.…”

Extracting Nucleon Strange and Anapole Form Factors from World Data

“…Vector meson dominance would suggest that the Q 2 evolution of the form factors be no more rapid than a dipole with mass parameter m 1 GeV. Similarly, lattice QCD simulations in the vicinity of the strange quark yield behavior consistent with a dipole of scale >1 GeV [18,19]. With the aim of fitting data up to Q 2 0:3 GeV 2 , approximating a dipole by a constant over this range would lead to less than 20% uncertainty (less than 10% at the next order in Q 2 ).…”