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Electromagnetic polarizabilities are fundamental properties of the proton that characterize its response to an external electromagnetic (EM) field. The generalization of the EM polarizabilities to non-zero four-momentum transfer opens up a powerful path to study the internal structure of the proton. They map out the spatial distribution of the polarization densities in the proton, provide access to key dynamical mechanisms that contribute to the electric and magnetic polarizability effects, and allow for the determination of fundamental characteristics of the system, such as the electric and magnetic polarizability radii. This article reviews our knowledge about proton EM generalized polarizabilities (GPs). An introduction is given to the basic concepts and the theoretical framework, which is then followed by a discussion that emphasizes the recent developments and findings of the virtual Compton scattering (VCS) experiments and future perspectives on the topic. [ABSTRACT FROM AUTHOR]

We document that p(γ,e+e−)p measurements will yield new, important information about the off-shell time-like nucleon form factors, especially in the φ meson region (q2=M2φ) governing the φN couplings gV,TφNN. Calculations for p(γ,e+e−)p, utilizing vector meson dominance, predict measurable φ enhancements at high &z.sfnc;t&z.sfnc; compared to the expected φ background production from π, η and Pomeron exchange. The φ form factor contribution generates a novel experimental signature for OZI violation and the proton strangeness content. The φN couplings are determined independently from a combined analysis of the neutron electric form factor and recent high &z.sfnc;t&z.sfnc; φ photoproduction. The π, η and Pomeron transition form factors are also predicted and the observed π and η transition moments are reproduced. [Copyright &y& Elsevier]

This review gives an update on virtual Compton scattering (VCS) off the nucleon, γ ∗ N → γ N , in the low-energy regime. We recall the theoretical formalism related to the generalized polarizabilities (GPs) and model predictions for these observables. We present the GP extraction methods that are used in the experiments: the approach based on the low-energy theorem for VCS and the formalism of Dispersion Relations. We then review the experimental results, with a focus on the progress brought by recent experimental data on proton GPs, and we conclude by some perspectives in the field of VCS at low energy. [ABSTRACT FROM AUTHOR]

We present an analysis of 13 observables in Compton scattering on the proton. Cross sections, asymmetries with polarised beam and/or targets, and polarisation-transfer observables are investigated for energies up to the Δ(1232) resonance to determine their sensitivity to the proton’s dipole scalar and spin polarisabilities. The Chiral Effective Field Theory Compton amplitude we use is complete at N4LO, 풪(e2δ4), for photon energies ω∼mπ, and so has an accuracy of a few per cent there. At photon energies in the resonance region, it is complete at NLO, 풪(e2δ0), and so its accuracy there is about 20%. We find that for energies from pion-production threshold to about 250 MeV, multiple asymmetries have significant sensitivity to presently ill-determined combinations of proton spin polarisabilities. We also argue that the broad outcomes of this analysis will be replicated in complementary theoretical approaches, e.g., dispersion relations. Finally, we show that below the pion-production threshold, 6 observables suffice to reconstruct the Compton amplitude, and above it 11 are required. Although not necessary for polarisability extractions, this opens the possibility to perform “complete” Compton-scattering experiments. An interactive Mathematica notebook, including results for the neutron, is available from judith.mcgovern@manchester.ac.uk. [ABSTRACT FROM AUTHOR]