Comments on the Starobinsky Model of Inflation and its Descendants
  We point out that the ability of some models of inflation, such as Higgs
inflation and the universal attractor models, in reproducing the available data
is due to their relation to the Starobinsky model of inflation. For large field
values, where the inflationary phase takes place, all these classes of models
are indeed identical to the Starobinsky model. Nevertheless, the inflaton is
just an auxiliary field in the Jordan frame of the Starobinsky model and this
leads to two important consequences: first, the inflationary predictions of the
Starobinsky model and its descendants are slightly different (albeit not
measurably); secondly the theories have different small-field behaviour,
leading to different ultra-violet cut-off scales. In particular, one
interesting descendant of the Starobinsky model is the non-minimally- coupled
quadratic chaotic inflation. Although the standard quadratic chaotic inflation
is ruled out by the recent Planck data, its non-minimally coupled version is in
agreement with observational data and valid up to Planckian scales.
