“…From the mathematical point of view, the study of nonlinear Schrödinger systems with quadratic interaction has been increasing in recent years. To cite a few, we refer the reader to [3], [4], [7], [8], [9], [12], [14], [15], [20], and references therein. An almost complete study of system (1.1) in L 2 (R n ) and H 1 (R n ) was undertaken in [9] (see also [7], [8]).…”