Bounces, turnarounds and singularities in bimetric gravity
  In this letter, we consider cosmological solutions of bimetric theory without assuming that only one metric is coupled to gravity. We conclude that any cosmology can be described by fixing the matter content of the space that we are not inhabiting. On the other hand, we show that some conclusions can still be extracted independently of the matter content filling both spaces. In particular, we can conclude the occurrence of some extremality events in one universe if we know that they take place in the other space. 
Salvatore Capozziello, Prado Martin-Moruno
gr-qc astro-ph.CO hep-th