“…The IVP associated to (1.5) has been studied in several publications (see for instance [2], [5], [6], [14], [15], [16], [33], [36], [37]) where among other qualitative properties local and global well-posedness issues were investigated. In particular, a global sharp well-posedness result was obtained by Guo and Wu [11] in H 1/2 (R) for initial data satisfying (1.8) u 0 2 2 ≤ 4π, see also [41]. The condition (1.8) guarantees the energy E(·) is positive via sharp Gagliardo-Nirenberg inequality.…”