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Ground States for a nonlinear Schr\"odinger system with sublinear coupling terms
We study the existence of ground states for the coupled Schr\"odinger system
\begin{equation} \left\{\begin{array}{lll} \displaystyle -\Delta
u_i+\lambda_i u_i= \mu_i |u_i|^{2q-2}u_i+\sum_{j\neq i}b_{ij}
|u_j|^q|u_i|^{q-2}u_i \\ u_i\in H^1(\mathbb{R}^n), \quad i=1,\ldots, d,
\end{array}\right. \end{equation} , for ,
(the so-called "symmetric attractive case") and
. We prove the existence of a nonnegative ground state
with radially decreasing. Moreover we show that,
for , such ground states are positive in all dimensions and for all
values of the parameters
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