  In braneworld cosmology the expanding Universe is realized as a brane moving
through a warped higher-dimensional spacetime. Like a moving mirror causes the
creation of photons out of vacuum fluctuations, a moving brane leads to
graviton production. We show that, very generically, Kaluza-Klein (KK)
particles scale like stiff matter with the expansion of the Universe and can
therefore not represent the dark matter in a warped braneworld. We present
results for the production of massless and KK gravitons for bouncing branes in
five-dimensional anti de Sitter space. We find that for a realistic bounce the
back reaction from the generated gravitons will be most likely relevant. This
letter summarizes the main results and conclusions from numerical simulations
which are presented in detail in a long paper [M.Ruser and R. Durrer, Phys.
Rev. D 76, 104014 (2007), arXiv:0704.0790]
