Speaker
Description
Spin observables yield a wealth of tests to our current understanding of
the nucleon internal structure. In particular, novel challenging
experimental data from Jefferson Lab have been published on the so-called
generalized spin polarizabilities, which quantify the spin-dependent
internal rearrangement of the nucleon probed by an external virtual photon.
We compute the resonance contribution to the nucleon spin structure
functions at low energy in the Witten-Sakai-Sugimoto model of holographic
QCD. Our analysis includes both spin 3/2 and spin 1/2 nucleon resonances
with positive and negative parity. We determine, in turn, the helicity
amplitudes for nucleon-resonance transitions and the resonance
contributions to the neutron and proton generalized spin polarizabilities.
Extrapolating the model parameters to realistic QCD data, our analysis
agrees with the observation that the ∆(1232) resonance gives the dominant
contribution to the forward spin polarizabilities at low momentum transfer.
As expected, the contribution of the ∆(1232) to the longitudinal-transverse
polarizabilities is instead negligible. Our analysis shows that different
spin 1/2 resonances give different contributions, in sign and magnitude, to
the generalized longitudinal-transverse spin polarizabilities.
