The Unity of Cosmological Attractors
  Recently, several broad classes of inflationary models have been discovered
whose cosmological predictions are stable with respect to significant
modifications of the inflaton potential. Some classes of models are based on a
non-minimal coupling to gravity. These models, which we will call
$\xi$-attractors, describe universal cosmological attractors (including Higgs
inflation) and induced inflation models. Another class describes conformal
attractors (including Starobinsky inflation and T-models) and their
generalization to $\alpha$-attractors. The aim of this paper is to elucidate
the common denominator of these models: their attractor properties stem from a
pole of order two in the kinetic term of the inflaton field in the Einstein
frame formulation, prior to switching to the canonical variables. We point out
that $\alpha$- and universal attractors differ in the subleading corrections to
the kinetic term. As a final step towards unification of $\xi$ and $\alpha$
attractors, we introduce a special class of $\xi$-attractors which is fully
equivalent to $\alpha$-attractors with the identification $\alpha = 1+{1\over
6\xi}$. There is no theoretical lower bound on $r$ in this class of models.
