Zygmund spaces, inviscid limits and uniqueness of Euler flows

The paper improves the classical uniqueness result for the Euler system in the $n$ dimensional case assuming that $\nabla u^E \in L_1(0,T;BMO(\Omega))$, only. Moreover the rate of the convergence for the inviscid limit of solutions to the Navier-Stokes equations is obtained, provided the same regularity of the limit Eulerian flow. A key element of the proof is a logarithmic inequality between the Hardy and $L_1$ spaces which is a consequence of the basic properties of the Zygmund space $\LlnL$.