Exploring extra dimensions through inflationary tensor modes
  Predictions of inflationary schemes can be influenced by the presence of
extra dimensions. This could be of particular relevance for the spectrum of
gravitational waves in models where the extra dimensions provide a brane-world
solution to the hierarchy problem. Apart from models of large as well as
exponentially warped extra dimensions, we analyze the size of tensor modes in
the Linear Dilaton scheme recently revived in the discussion of the "clockwork
mechanism". The results are model dependent, significantly enhanced tensor
modes on one side and a suppression on the other. In some cases we are led to a
scheme of "remote inflation", where the expansion is driven by energies at a
hidden brane. In all cases where tensor modes are enhanced, the requirement of
perturbativity of gravity leads to a stringent upper limit on the allowed
Hubble rate during inflation.
