The CR Paneitz operator and the stability of CR pluriharmonic functions

We give a condition which ensures that the Paneitz operator of an embedded three-dimensional CR manifold is nonnegative and has kernel consisting only of the CR pluriharmonic functions. Our condition requires uniform positivity of the Webster scalar curvature and the stability of the CR pluriharmonic functions for a real analytic deformation. As an application, we show that the real ellipsoids in C2C2 are such that the CR Paneitz operator is nonnegative with kernel consisting only of the CR pluriharmonic functions.