“…The scaling critical index s = −1 of (1.1) for n = 2 suggests well-posedness in the range −1 ≤ s. In particular, in view of the conservation of mass, it is a natural question whether L 2 -well-posedness holds true. Before stating the main result, we introduce the symmetrized equation of (1.1) by performing a linear change of variables as in [6]. Put x = 4 −1/3 x 1 + √ 34 −1/3 x 2 , y = 4 −1/3 x 1 − √ 34 −1/3 x 2 and v(t, x, y) := u(t, x 1 , x 2 ), v 0 (x, y) := u 0 (x 1 , x 2 ).…”