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 Q 2 > 0. The dominant low energy amplitudes are represented in our calculation by one-pion-loop graphs of relativistic baryon chiral pertu...

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Bibliographic Details
Published in:Nuclear physics. A 1998-10, Vol.641 (1), p.119-130
Main Authors: Edelmann, J, Kaiser, N, Piller, G, Weise, W
Format: Article
Language:English
Subjects:
Generalized polarizability sum rules
Pion loops
Δ-resonance
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Summary: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 Q 2 > 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 Σ p( Q 2) with empirical values obtained from integrating up electroproduction data for Q 2 < 0.4 GeV 2. The proton spin-polarizability γ p( Q 2) switches sign around Q 2 = 0.4 GeV 2 and it joins smoothly the “partonic” curve, extracted from polarized deep-inelastic scattering, around Q 2 = 0.7 GeV 2. For the neutron our predictions of Σ n( Q 2) and γ n( Q 2) agree reasonably well at Q 2 = 0 with existing determinations. Upcoming (polarized) electroproduction experiments will be able to test the generalized polarizability sum rules investigated here.
ISSN:0375-9474
DOI:10.1016/S0375-9474(98)00467-9