The Euler–Korteweg system consists of a quasi-linear, dispersive perturbation of the Euler equations. The Cauchy problem has been studied in any dimension d ≥ 1 by Benzoni, Danchin, and Descombes, who obtained local well-posedness results when the velocity is in Hs for s > d/2 + 1. They noticed that one may expect to find some smoothing effect due to the dispersive effects, but there was no pro...