Gravitational Born amplitudes and kinematical constraints

It is shown that in the Born approximation the helicity amplitudes for graviton-graviton scattering are completely determined by kinematical considerations alone, without detailed Feynman graph calculations, reflecting thus the uniqueness of pure Einstein theory. It is shown that the nonuniqueness of the matter-graviton amplitudes is related to the existence of nonminimal interactions. In the presence of such interactions, helicity is not conserved in elastic scattering of massless particles. A simplified three-graviton vertex with two on-shell gravitons is presented