, Volume 67, Issue 1, pp 281-306

On nonlinear Schrödinger equations, II.H S -solutions and unconditional well-posedness

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We consider the nonlinear Schrödinger equation (NLS) (see below) with a general “potential”F(u), for which there are in general no conservation laws. The main assumption onF(u) is a growth rateO(|u| k ) for large |u|, in addition to some smoothness depending on the problem considered. A uniqueness theorem is proved with minimal smoothness assumption onF andu, which is useful in eliminating the “auxiliary conditions” in many cases. A new local existence theorem forH S -solutions is proved using an auxiliary space of Lebesgue type (rather than Besov type); here the main assumption is thatk≤1+4/(m−2s) ifs<m/2,k<∞ ifs=m/2 (no assumption ifs>m/2). Moreover, a general existence theorem is proved for globalH S -solutions with small initial data, under the main additional condition thatF(u)=O(|u|1+4/m) for small |u|; in particularF(u) need not be (quasi-) homogeneous or in the critical case. The results are valid for alls≥0 ifm≤6; there are some restrictions ifm≥7 and ifF(u) isnot a polynomial inu and\(\bar u\).