A remark on norm inflation for nonlinear Schr\"odinger equations

We consider semilinear Schr"odinger equations with nonlinearity that is a polynomial in the unknown function and its complex conjugate, on ${\mathbb{R}}^d$ or on the torus. Norm inflation (ill-posedness) of the associated initial value problem is proved in Sobolev spaces of negative indices. To this end, we apply the argument of Iwabuchi and Ogawa (2012), who treated quadratic nonlinearities. This method can be applied whether the spatial domain is non-periodic or periodic and whether the nonlinearity is gauge/scale-invariant or not.