Inflationary behavior of $R^2$ gravity in a conformal framework

Understand

Models of inflation are tightly constrained by the PLANCK satellite data.

• Among them, Starobinsky's model with an exponential type potential seems to be challenged by the recent BICEP2 results.
• The model is based on the existence of $\,~ R^2$ terms in the Einstein-Hilbert action, which have their origin in the conformal-anomaly.
• Conformal (or Weyl) gravitational theories are relevant when matter fields become effectively massless; i.e.