Nucleon Polarizibilities for Virtual Photons
نویسنده
چکیده
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 cross sections are represented in our calculation by one-pionloop graphs of relativistic baryon chiral perturbation theory and the ∆(1232)-resonance excitation. For the proton we find good agreement of the calculated Σp(Q 2) with empirical values obtained from integrating up electroproduction data for Q2 < 0.4 GeV2. The proton spin-polarizability γp(Q 2) 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(Q 2) and γn(Q 2) 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. Work supported in part by DFG and BMBF.
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