Spin-flavor structure of chiral-odd generalized parton distributions in the large-Nc limit

We study the spin-flavor structure of the nucleon's chiral-odd generalized parton distributions (transversity GPDs) in the large-Nc limit of QCD. In contrast to the chiral-even case, only three combinations of the four chiral-odd GPDs are nonzero in the leading order of the 1/Nc expansion: E-barT = ET+2H-tildeT, HT, and E-tildeT. The degeneracy is explained by the absence of spin-orbit interactions correlating the transverse momentum transfer with the transverse quark spin. It can also be deduced from the natural Nc scaling of the quark-nucleon helicity amplitudes associated with the GPDs. In the GPD E-barT the flavor-singlet component u+d is leading in the 1/Nc expansion, while in HT and E-tildeT it is the flavor-nonsinglet components u–d. Furthermore, the large-Nc relations are consistent with the spin-flavor structure extracted from hard exclusive π0 and η electroproduction data, if it is assumed that the processes are mediated by twist-3 amplitudes involving the chiral-odd GPDs and the chiral-odd pseudoscalar meson distribution amplitudes.