Universality Classes of Scale Invariant Inflation
  We investigate the inflationary implications of extensions of Poincare
symmetry. The simplest constructions with local scale invariance lead to
universal predictions: the spectral index is $n_s = 1-2/N$, in excellent
agreement with Planck data, while the tensor-to-scalar ratio is determined by a
free parameter to $r = 12 \alpha / N^2$. For the special value $\alpha=1$ one
finds symmetry enhancement to the full conformal group. We show that these
findings hold both for two-derivative scalar-tensor theories as well as
higher-derivative gravity. Therefore scale invariance underlies a promising set
of inflationary models.
