Abstract
We consider the Zakharov system in the energy critical dimension d = 4 with energy below the ground state. It is known that below the ground state solutions exist globally in time, and scatter in the radial case. Scattering below the ground state in the non-radial case is an open question. We show that if scattering fails, then there exists a minimal energy non-scattering solu-tion below the ground state. Moreover the orbit of this solution is precompact modulo translations. The proof follows by a concentration compactness argu-ment, together with a refined small data theory for energy dispersed solutions.