Speaker
Robert Schneider
(LMU)
Description
We derive the modified Friedmann equations for a generalization of the DGP model, in which the brane has one additional compact dimension. The main new feature is the emission of gravitational waves into the bulk. If the compact dimension is stabilized, these waves vanish and one recovers DGP cosmology. However, a stabilization by means of physical matter is not possible for a tension-dominated brane, implying a late time modification of 4D cosmology different from DGP. For a freely expanding compact direction, we find attractor solutions with zero 4D Hubble parameter despite the presence of a 4D cosmological constant. The model hence constitutes an example of dynamical degravitation at the full nonlinear level. Without stabilization, however, there is no 4D regime and the model is ruled out observationally., as we demonstrate explicitly by comparing to supernova data.
