Inflationary Perturbations in No-Scale Theories
  We study the inflationary perturbations in general (classically)
scale-invariant theories. Such scenario is motivated by the hierarchy problem
and provides natural inflationary potentials and dark matter candidates. We
analyse in detail all sectors (the scalar, vector and tensor perturbations)
giving general formulae for the potentially observable power spectra, as well
as for the curvature spectral index $n_s$ and the tensor-to-scalar ratio $r$.
We show that the conserved Hamiltonian for all perturbations does not feature
negative energies even in the presence of the Weyl-squared term if the
appropriate quantization is performed and argue that this term does not lead to
phenomenological problems at least in some relevant setups. The general
formulae are then applied to a concrete no-scale model, which includes the
higgs and a scalar, "the planckion", whose vacuum expectation value generates
the Planck mass. Inflation can be triggered by a combination of the planckion
and the Starobinsky scalar and we show that no tension with observations is
present even in the case of pure planckion-inflation, if the coefficient of the
Weyl-squared term is large enough. In general, even quadratic inflation is
allowed in this case. Moreover, the Weyl-squared term leads to an isocurvature
mode, which currently satisfies the observational bounds, but may be detectable
with future experiments.
