Baryon to meson transition distribution amplitudes (TDAs) extend the concept of generalized parton distributions. Baryon to meson TDAs appear as building blocks in the collinear factorized description of amplitudes for a class of hard exclusive reactions, prominent examples of which being hard exclusive meson electroproduction off a nucleon in the backward region and baryonantibaryon annihilation into a meson and a lepton pair. We study the general properties of these objects following from the underlying symmetries of QCD. In particular, the Lorentz symmetry results in the polynomiality property of the Mellin moments in longitudinal momentum fractions.We present a detailed account of the isotopic and permutation symmetry properties of nucleon to pion (πN ) TDAs. This restricts the number of independent leading twist πN TDAs to eight functions, providing description of all isotopic channels. Using chiral symmetry and the crossing relation between πN TDAs and πN generalized distribution amplitudes we establish soft pion theorems for πN TDAs, which determine the magnitude of πN TDAs. Finally, we build a simple resonance exchange model for πN TDAs considering N and ∆(1232) exchange contributions into the isospin-1 2 and isospin-3 2 πN TDAs.

The extension of the concept of generalized parton distributions leads to the introduction of baryon to meson transition distribution amplitudes (TDAs), non-diagonal matrix elements of the nonlocal three quark operator between a nucleon and a meson state. We present a general framework for modelling nucleon to pion (πN ) TDAs. Our main tool is the spectral representation for πN TDAs in terms of quadruple distributions. We propose a factorized Ansatz for quadruple distributions with input from the soft-pion theorem for πN TDAs. The spectral representation is complemented with a D-term like contribution from the nucleon exchange in the cross channel. We then study backward pion electroproduction in the QCD collinear factorization approach in which the non-perturbative part of the amplitude involves πN TDAs.Within our two component model for πN TDAs we update previous leading-twist estimates of the unpolarized cross section. Finally, we compute the transverse target single spin asymmetry as a function of skewness. We find it to be sizable in the valence region and sensitive to the phenomenological input of our πN TDA model.