L2-CONCENTRATION PHENOMENON FOR ZAKHAROV SYSTEM BELOW ENERGY NORM.

In this paper, we prove an L2-concentration result of Zakharov system in space dimension two, with radial initial data $(u_0,n_0,n_1) \in H^s \times L^2 \times H^{-1} (\frac{16}{17} < s < 1)$, when blow up of the solution happens by I-method. In addition to that, we find a blow up character of this system. Furthermore, we improve the global existence result of Bourgain's to the above-mentioned spaces. [ABSTRACT FROM AUTHOR]