On the scattering operators for ACHE metrics of Bergman type on strictly pseudoconvex domains

The scattering operators associated to an ACHE metric of Bergman type on a strictly pseudoconvex domain are a one-parameter family of CR-conformally invariant pseudo-differential operators of Heisenberg class with respect to the induced CR structure on the boundary. In this paper, we mainly show that if the boundary Webster scalar curvature is positive, then for γ∈(0,1) the renormalised scattering operator P2γ has positive spectrum and satisfies the maximum principal; moreover, the fractional curvature Q2γ is also positive. This is parallel to the result of Guillarmou-Qing [16] for the real case. We also give two energy extension formulae for P2γ, which are parallel to the energy extension given by Chang-Case [2] for the real case.