Nonminimal coupling and inflationary attractors
  We show explicitly how the T model, E model, and Hilltop inflations are obtained from the general scalar-tensor theory of gravity with arbitrary conformal factors in the strong coupling limit. We argue that $\xi$ attractors can give any observables $n_s$ and $r$ by this method. The existence of attractors imposes a challenge to distinguish different models. 
Zhu Yi and Yungui Gong
gr-qc astro-ph.CO hep-th