Mean Field Limits in Strongly Confined Systems

Abstract: We consider the dynamics of $N$ interacting bosons in three dimensions which are strongly confined in one or two directions. We analyze the two cases where the interaction potential $w$ is rescaled by either $N^{-1}w(\cdot)$ or $a^{3\theta-1}w(a^\theta \cdot)$ and choose the initial wavefunction to be close to a product wavefunction. For both scalings we prove that in the mean field limit $N\rightarrow \infty $ the dynamics of the $N$-particle system are described by a nonlinear equation in one or two dimensions. In the case of the scaling $N^{-1}w(\cdot)$ this equation is the Hartree equation and for the scaling $a^{3\theta-1}w(a^\theta \cdot) $ the nonlinear Schr\"odinger equation. In both cases we obtain explicit bounds for the rate of convergence of the $N$-particle dynamics to the one-particle dynamics.