On the Chern–Moser–Weyl tensor of real hypersurfaces

抄録

We derive an explicit formula for the well-known Chern–Moser–Weyl tensor for nondegenerate real hypersurfaces in complex space in terms of their defining functions. The formula is considerably simplified when applying to “pluriharmonic perturbations” of the sphere or to a Fefferman approximate solution to the complex Monge–Ampère equation. As an application, we show that the CR invariant one-form 𝑋_𝛼 constructed recently by Case and Gover is nontrivial on each real ellipsoid of revolution in ℂ³, unless it is equivalent to the sphere. This resolves affirmatively a question posed by these two authors in 2017 regarding the (non-) local CR invariance of the ℐ'-pseudohermitian invariant in dimension five and provides a counterexample to a recent conjecture by Hirachi.