Planck mass and inflation as consequences of dynamically broken scale
  invariance
  Classical scale invariance represents a promising framework for model
building beyond the Standard Model. However, once coupled to gravity, any
scale-invariant microscopic model requires an explanation for the origin of the
Planck mass. In this paper, we provide a minimal example for such a mechanism
and show how the Planck mass can be dynamically generated in a strongly coupled
gauge sector. We consider the case of hidden SU(N_c) gauge interactions that
link the Planck mass to the condensation of a scalar bilinear operator that is
nonminimally coupled to curvature. The effective theory at energies below the
Planck mass contains two scalar fields: the pseudo-Nambu--Goldstone boson of
spontaneously broken scale invariance (the dilaton) and a gravitational scalar
degree of freedom that originates from the R^2 term in the effective action
(the scalaron). We compute the effective potential for the coupled
dilaton-scalaron system at one-loop order and demonstrate that it can be used
to successfully realize a stage of slow-roll inflation in the early Universe.
Remarkably enough, our predictions for the primordial scalar and tensor power
spectra interpolate between those of standard R^2 inflation and linear chaotic
inflation. For comparatively small gravitational couplings, we thus obtain a
spectral index n_s ~= 0.97 and a tensor-to-scalar ratio as large as r ~= 0.08.
