Electromagnetic polarizabilities and the excited states of the nucleon

The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant αp(E0+) = +3.2, αn(E0+) = +4.1, the t-channel α t p,n = −βt p,n = +7.6 and the resonant βp,n(P33(1232)) = +8.3 contributions (in units of 10 −4fm). The remaining deviations from the experimental data ∆αp = 1.2 ± 0.6, ∆βp = 1.2 ∓ 0.6, ∆αn = 0.8 ± 1.7 and ∆βn = 2.0 ∓ 1.8 are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of twophoton coupling to the σ meson having the predicted mass mσ = 666 MeV and two-photon width Γγγ = 2.6 keV. PACS. 11.55.Fv Dispersion relations – 11.55.Hx Sum rules – 13.60.Fz Elastic and Compton scattering – 14.70.Bh Photons