MOMENTS AND HUYGENS PRINCIPLE FOR CONFORMALLY INVARIANT FIELD-EQUATIONS IN CURVED SPACE-TIMES

By means of a certain conformal covariant differentiation process we define an infinite sequence of conformally invariant tensors (moments) for Weyl's neutrino equation in a curved space-time. In the cases of the conformally invariant-scalar wave equation and Maxwell's equations such moments were introduced by Gunther. We prove some properties of the moments and study the relationship between the moments and the validity of Huygens' principle for these conformally invariant field equations. Using suitable generating systems of conformally invariant tensors we derive the first moment equations and obtain from them results on Huygens' principle.