Well-Posedness for the Extended Schrödinger–Benjamin–Ono System

In this work we prove that the initial value problem associated to the Schrödinger–Benjamin–Ono type system i ∂ t u + ∂ x 2 u = u v + β u | u | 2 , ∂ t v - H x ∂ x 2 v + ρ v ∂ x v = ∂ x ( | u | 2 ) u ( x , 0 ) = u 0 ( x ) , v ( x , 0 ) = v 0 ( x ) , with β , ρ ∈ R is locally well-posed for initial data ( u 0 , v 0 ) ∈ H s + 1 2 ( R ) × H s ( R ) for s > 5 4 . Our method of proof relies on energy methods and compactness arguments. However, due to the lack of symmetry of the nonlinearity, the usual energy has to be modified to cancel out some bad terms appearing in the estimates. Finally, in order to lower the regularity below the Sobolev threshold s = 3 2 , we employ a refined Strichartz estimate introduced in the Benjamin–Ono setting by Koch and Tzvetkov, and further developed by Kenig and Koenig.