Unitarity constraints on neutral pion electroproduction

At large virtuality $Q^2$, the coupling to the vector meson production channels provides us with a natural explanation of the surprisingly large cross section of the neutral pion electroproduction recently measured at Jefferson Laboratory, without destroying the good agreement between the Regge pole model and the data at the real photon point. Elastic rescattering of the $\pi^0$ provides us with a way to explain why the node, that appears at $t\sim -0.5$ GeV$^2$ at the real photon point, disappears as soon as $Q^2$ differs from zero.