Edholm, James (2017) UV completion of the Starobinsky model, tensor-to-scalar ratio, and constraints on nonlocality. Physical Review D, 95 (4): 044004. ISSN 1550-7998
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Abstract
In this paper, we build upon the successes of the ultraviolet (UV) completion of the Starobinsky model of inflation. This involves an extension of the Einstein-Hilbert term by an infinite covariant derivative theory of gravity which is quadratic in curvature. It has been shown that such a theory can potentially resolve the cosmological singularity for a flat, homogeneous and isotropic geometry, and now it can also provide a successful cosmological inflation model, which in the infrared regime matches all the predictions of the Starobinsky model of inflation. The aim of this paper is to show that the tensor-to-scalar ratio is modified by the scale of nonlocality, and in general a wider range of tensor-to-scalar ratios can be obtained in this class of model, which can put a lower bound on the scale of nonlocality for the first time as large as the O(10^14) GeV.