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-N-c 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/N-c expansion: (E) over bar (T) = E-T + 2 (H) over tilde (T), H-T, and (E) over tilde (T). 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 N-c scaling of the quark-nucleon helicity amplitudes associated with the GPDs. In the GPD (E) over bar (T) the flavor-singlet component u + d is leading in the 1/N-c expansion, while in HT and (E) over tilde (T) it is the flavor-nonsinglet components u - d. The large-Nc relations are consistent with the spin-flavor structure extracted from hard exclusive pi(0) and eta 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.