The envelope of holomorphy of a model third-degree surface and the rigidity phenomenon

The structures of the graded Lie algebra aut Q infinitesimal automorphisms of a cubic (a model surface in ?^N) and the corresponding group Aut Q of its holomorphic automorphisms are studied. It is proved that for any nondegenerate cubic, the positively graded components of the algebra aut Q are trivial and, as a consequence, Aut Q has no subgroups consisting of nonlinear automorphisms of the cubic that preserve the origin (the so-called rigidity phenomenon). In the course of the proof, the envelope of holomorphy for a nondegenerate cubic is constructed and shown to be a cylinder with respect to the cubic variable whose base is a Siegel domain of the second kind.     

Tritiumausbeute der Reaktion He4 (γ,p) H3 mit 44 und 54 MeV-Bremsstrahlung

The photo disintegration of the α-particle was investigated by counting the tritium accumulated during irradiation with a low-level gas counting system. The measured yield is compared with values calculated from published cross-section data.