Ground state mass concentration in the L^2-critical nonlinear Schrodinger equation below H^1

Abstract

We consider finite time blowup solutions of the $L^2$-critical cubic focusing nonlinear Schr\"odinger equation on $\R^2$. Such functions, when in $H^1$, are known to concentrate a fixed $L^2$-mass (the mass of the ground state) at the point of blowup. Blowup solutions from initial data that is only in $L^2$ are known to concentrate at least a small amount of mass. In this paper we consider the intermediate case of blowup solutions from initial data in $H^s$, with $1 > s > s_Q$, where $s_Q \le \sQ$. Our main result is that such solutions, when radially symmetric, concentrate at least the mass of the ground state at the origin at blowup time.