What do we know about theQ2evolution of the Gerasimov-Drell-Hearn sum rule?

QED radiative corrections in processes of exclusive pion electroproduction

“…AO (Amplitude and Observables) [35]. The amplitudes are parameterized as follows: S-channel resonances are parameterized with relativistic Breit-Wigner forms with momentum-dependent widths.…”

Photoproduction of nucleon resonances and nucleon spin structure function in the resonance region

“…[15,27], is absorbed into Eq. (19), and the first term in the above equation is just the usual charge operator. All of those charge operators related to the two-body exchange currents are O (1/m 3 ), and can be neglected in the calculation of σ T L , although they are crucial in the case of the γN → ∆ E2 transition [9] process and in reproducing the neutron charge radius [10].…”

The Q2-dependence of the generalised Gerasimov–Drell–Hearn integral for the proton

“…(2). Burkert and Li [9] parameterised the experimental Q 2 -evolution of the main nucleon resonances (P 33 (1232), P 11 (1440), S 11 (1535), D 13 (1520), F 15 (1680)), and assumed single-quark transitions to evaluate the contributions from other resonances. Aznauryan [10] described the resonance excitation in the approximation of infinitely narrow resonances, and included a contribution from one-pion exchange in the near-threshold region.…”

“…As Q 2 → 0, I GDH (Q 2 ) must change sign in order to reach the negative value predicted by the GDH sum rule at Q 2 = 0. Several phenomenological models have been proposed to describe the dependence of the generalised GDH integral on Q 2 [7][8][9][10][11]. Some of these models predict large effects from nucleon-resonance excitation [9,10] or from higher twist [7,11], even for Q 2 up to a few GeV 2 .…”

“…Several phenomenological models have been proposed to describe the dependence of the generalised GDH integral on Q 2 [7][8][9][10][11]. Some of these models predict large effects from nucleon-resonance excitation [9,10] or from higher twist [7,11], even for Q 2 up to a few GeV 2 . Other models based on chiral perturbation theory have been proposed but their application is limited to Q 2 1 GeV 2 [12].…”