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Register a new userAnalytic continuation of nucleon electromagnetic form factors in the time-like region
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The possibility to compute nucleon electromagnetic form factors in the time-like region by analytic continuation of their space-like expressions has been explored in the framework of the Skyrme model. We have developed a procedure to solve analytically Fourier transforms of the nucleon electromagnetic current and hence to obtain form factors defined in all kinematical regions and fulfilling the first-principles requirements. The results are discussed and compared to data, both in space-like and time-like region.
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Some recent advances in the theoretical description of the Nucleon electromagnetic form factors, both in the space- and time-like regions, will be briefly illustrated. In particular, both the present stage of the lattice calculations and updated phenomenological approaches, like the ones based on dispersion relations and on microscopical models, will be reported.
The role of the strange quarks on the low-energy interactions of the proton can be probed through the strange electromagnetic form factors. Knowledge of these form factors provides essential input for parity-violating processes and contributes to the understanding of the sea quark dynamics. We determine the strange electromagnetic form factors of the nucleon within the lattice formulation of Quantum Chromodynamics using simulations that include light, strange and charm quarks in the sea all tuned to their physical mass values. We employ state-of-the-art techniques to accurately extract the form factors for values of the momentum transfer square up to 0.8~GeV$^2$. We find that both the electric and magnetic form factors are statistically non-zero. We obtain for the strange magnetic moment $mu^s=-0.017(4)$, the strange magnetic radius $langle r^2_M rangle^s=-0.015(9)$~fm$^2$, and the strange charge radius $langle r^2_E rangle^s=-0.0048(6)$~fm$^2$.
The nucleon electromagnetic form factors are calculated in light cone QCD sum rules framework using the most general form of the nucleon interpolating current. Using two forms of the distribution amplitudes (DAs), predictions for the form factors are presented and compared with existing experimental data. It is shown that our results describe remarkably well the existing experimental data.
We present a comprehensive analysis of the spacelike nucleon electromagnetic form factors and their flavor decomposition within the framework of light-front holographic QCD. We show that the inclusion of the higher Fock components $ket {qqqqbar{q}}$ has a significant effect on the spin-flip elastic Pauli form factor and almost zero effect on the spin-conserving Dirac form factor. We present light-front holographic QCD results for the proton and neutron form factors at any momentum transfer range, including asymptotic predictions, and show that our results agree with the available experimental data with high accuracy. In order to correctly describe the Pauli form factor we need an admixture of a five quark state of about 30$%$ in the proton and about 40$%$ in the neutron. We also extract the nucleon charge and magnetic radii and perform a flavor decomposition of the nucleon electromagnetic form factors. The free parameters needed to describe the experimental nucleon form factors are very few: two parameters for the probabilities of higher Fock states for the spin-flip form factor and a phenomenological parameter $r$, required to account for possible SU(6) spin-flavor symmetry breaking effects in the neutron, whereas the Pauli form factors are normalized to the experimental values of the anomalous magnetic moments. The covariant spin structure for the Dirac and Pauli nucleon form factors prescribed by AdS$_5$ semiclassical gravity incorporates the correct twist scaling behavior from hard scattering and also leads to vector dominance at low energy.
We present results from a calculation of the electromagnetic transition form factors between ground-state octet and decuplet baryons as well as the octet-only $Sigma^0$ to $Lambda$ transition. We work in the combined framework of Dyson-Schwinger equations and covariant Bethe-Salpeter equations with all elements, the baryon three body wave function, the quark propagators and the dressed quark-photon vertex determined from a well-established, momentum dependent approximation for the quark-gluon interaction. We discuss in particular the similarities among the different transitions as well as the differences induced by SU(3)-isospin symmetry breaking. We furthermore provide estimates for the slopes of the electric and magnetic $Sigma^0$ to $Lambda$ transitions at the zero photon momentum point.
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