Graviton scattering in an M-orientifold background
  In this paper we study the scattering of gravitons off a five orientifold in eleven dimensions. We compare the supergravity result with a two loop M(atrix) model calculation and find exact agreement. The supergravity calculation involves nonlinear three graviton effects. 
Ulf H. Danielsson, Par Stjernberg, Martin Kruczenski