Nucleon polarizabilities for virtual photons

We generalize the sum rules for the nucleon electric plus magnetic polarizability Σ=α+β and for the nucleon spin-polarizability γ, to virtual photons with Q2>0. The dominant low energy amplitudes are represented in our calculation by one-pion-loop graphs of relativistic baryon chiral perturbation theory and the Δ(1232)-resonance excitation. For the proton we find good agreement of the calculated Σp(Q2) with empirical values obtained from integrating up electroproduction data for Q2<0.4 GeV2. The proton spin-polarizability γp(Q2) switches sign around Q2=0.4 GeV2 and it joins smoothly the ''partonic'' curve, extracted from polarized deep-inelastic scattering, around Q2=0.7 GeV2. For the neutron our predictions of Σn(Q2) and γn(Q2) agree reasonably well at Q2=0 with existing determinations. Upcoming (polarized) electroproduction experiments will be able to test the generalized polarizability sum rules investigated here. (orig.)