Simultaneous expansion and rotation of shear-free universes in modified   gravity
  We show in a fully covariant way that, there exist a class of $f(R)$ models for which a shear-free, almost FLRW universe can expand and rotate at the same time . 
Amare Abebe, Rituparno Goswami and Peter K.S. Dunsby
gr-qc hep-th