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 ns=1−2/N, in excellent
agreement with Planck data, while the tensor-to-scalar ratio is determined by a
free parameter to r=12α/N2. For the special value α=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.Comment: 6 pages, 1 figur