Baryon distribution amplitude: Large-Nc factorization, spin-flavor symmetry and soft-pion theorem

The 1/N_c expansion for the baryon distribution amplitude is constructed in terms of a specially designed generating functional. At large N_c this functional shows exponential behavior. The exponential factor is universal for all low-lying baryons and baryon-meson scattering states. Simple factorization properties are established for the preexponential term. This factorization agrees with the large-N_c contracted SU(2N_f) spin-flavor symmetry. The consistency of the factorization with the soft-pion theorem for the baryon distribution amplitude is explicitly checked. A relation between the generating functionals for the distribution amplitudes of the nucleon and the Delta resonance is derived.