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

Abstract

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. their masses are negligible in comparison with the spacetime curvature. These theories may include other, additional scalar fields. We show that their presence under general conditions does not destabilize the inflationary behaviour encountered in the Starobinsky model, although the issue of the exact quantitative agreement with existing data, like the tensor to scalar ratio, rests on the choice of parameters.

17 pages, 8 figures, revised version, references and text added, typos corrected

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• Effective Field Theory for Inflation
• Cosmological Dark Energy: Prospects for a Dynamical Theory
• Ghost Constraints on Modified Gravity
• The Imaginary Starobinsky Model
• Resurrecting Quadratic Inflation in No-Scale Supergravity in Light of BICEP2
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Cited by in corpus (2)

• Restricted Weyl invariance in four-dimensional curved spacetime
• Reconciling Induced-Gravity Inflation in Supergravity With The Planck 2013 & BICEP2 Results