Existence and stability of standing waves for coupled nonlinear Hartree type equations

We study existence and stability of standing waves for coupled nonlinear Hartree type equations $$-i\frac{\partial}{\partial t}\psi_j=\Delta \psi_j+\sum_{k=1}^m \left(W\star |\psi_k|^p \right)|\psi_j|^{p-2}\psi_j,$$ where $\psi_j:\mathbb{R}^N\times \mathbb{R}\to \mathbb{C}$ for $j=1, \ldots, m$ and the potential $W:\mathbb{R}\to [0, \infty)$ satisfies certain assumptions. Our method relies on a variational characterization of standing waves based on minimization of the energy when $L^2$ norms of component waves are prescribed. We obtain existence and stability results for two and three-component systems and for a certain range of $p$. In particular, our argument works in the case when $W(x)=|x|^{-\alpha}$ for some $\alpha>0.$