On global well-posedness of the modified KdV equation in modulation spaces

We study well-posedness of the complex-valued modified KdV equation (mKdV) on the real line. In particular, we prove local well-posedness of mKdV in modulation spaces $M^{2,p}_{s}(mathbb{R})$ for $s ge frac14$ and $2leq p < infty$. For $s < frac 14$, we show that the solution map for mKdV is not locally uniformly continuous in $M^{2,p}_{s}(mathbb{R})$. By combining this local well-posedness with our previous work (2018) on an a priori global-in-time bound for mKdV in modulation spaces, we also establish global well-posedness of mKdV in $M^{2,p}_{s}(mathbb{R})$ for $s ge frac14$ and $2leq p < infty$.