Poincaré-Dulac normal form reduction for unconditional well-posedness of the periodic cubic NLS

Abstract

We implement an infinite iteration scheme of Poincare-Dulac normal form reductions to establish an energy estimate on the one-dimensional cubic nonlinear Schrodinger equation (NLS) in C_t L^2(T), without using any auxiliary function space. This allows us to construct weak solutions of NLS in C_t L^2(T)$ with initial data in L^2(T) as limits of classical solutions. As a consequence of our construction, we also prove unconditional well-posedness of NLS in H^s(T) for s \geq 1/6.

28 pages. In Section 3, we now use (ordered) trees for indexing multilinear terms appearing in the process (instead of assuming that the time derivative falls on the first factor as in the previous version.)