The Tensor Desert
  We consider the question of whether it is worth building an experiment with the sole purpose of bringing the detectable limit on the tensor-to-scalar ratio, r, down to 10^{-3}. We look at the inflationary models which give a prediction in this region and recap the current situation with the tensor mode, showing that there are only three known models of inflation which give definitive predictions in the region 10^{-3}<r<10^{-2}. 
Laila Alabidi