Frame-dependence of higher-order inflationary observables in scalar-tensor theories

Abstract

In the context of scalar-tensor theories of gravity we compute the third-order corrected spectral indices in the slow-roll approximation. The calculation is carried out by employing the Green's function method for scalar and tensor perturbations in both the Einstein and Jordan frames. Then, using the interrelations between the Hubble slow-roll parameters in the two frames we find that the frames are equivalent up to third order. Since the Hubble slow-roll parameters are related to the potential slow-roll parameters, we express the observables in terms of the latter which are manifestly invariant. Nevertheless, the same inflaton excursion leads to different predictions in the two frames since the definition of the number of e-folds differs. To illustrate this effect we consider a nonminimal inflationary model and find that the difference in the predictions grows with the nonminimal coupling and it can actually be larger than the difference between the first and third order results for the observables. Finally, we demonstrate the effect of various end-of-inflation conditions on the observables. These effects will become important for the analyses of inflationary models in view of the improved sensitivity of future experiments.

Title changed per journal request, typos fixed, a few comments and references added, to appear in PRD

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Cited by in corpus (8)

• Selected topics in scalar-tensor theories and beyond
• Coleman-Weinberg linear inflation: metric vs. Palatini formulation
• Equivalence of inflationary models between the metric and Palatini formulation of scalar-tensor theories
• Dynamical equivalence of $f(R)$ gravity in Jordan and Einstein frames
• Note on stability in conformally connected frames
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• Formalizing Slow-roll Inflation in Scalar-Tensor Theories of Gravitation
• Scale Invariant Gravity and Black Hole Ringdown