Stable solitary waves with prescribed $L^2$-mass for the cubic Schr\"odinger system with trapping potentials

For the cubic Schr"odinger system with trapping potentials in ${\mathbb{R}}^N$, $N\le 3$, or in bounded domains, we investigate the existence and the orbital stability of standing waves having components with prescribed $L^2$-mass. We provide a variational characterization of such solutions, which gives information on the stability through of a condition of Grillakis-Shatah-Strauss type. As an application, we show existence of conditionally orbitally stable solitary waves when: a) the masses are small, for almost every scattering lengths, and b) in the defocusing, weakly interacting case, for any masses.