Cosmology in nonlocal gravity

Sravan Kumar, Alexey S. Koshelev, Alexei A. Starobinsky

Research output: Chapter in Book/Report/Conference proceedingChapter (peer-reviewed)peer-review

Abstract

In this chapter we review the recent developments of realizing R2-like inflation in the framework of a most general UV nonlocal extension of Einstein’s general theory of relativity (GR). It is a well-motivated robust approach toward quantum gravity. In the past decades, nonlocal gravitational theories that are quadratic in curvature have been understood to be ghost-free and super-renormalizable around maximally symmetric spacetimes. However, in the context of early Universe cosmology, we show that one must go beyond the quadratic curvature nonlocal gravity in order to achieve a consistent ghost-free framework of Universe evolution from quasi-de Sitter to Minkowski spacetime. In this regard, we discuss a construction of a most general nonlocal gravity action that leads to R2-like inflation and discuss the corresponding observational predictions for the scalar and tensor spectral tilts, tensor-to-scalar ratio, and the primordial non-Gaussianities. We present an analysis of how the nonlocal inflationary cosmology goes beyond the established notions of effective field theories of inflation. Finally, we comment on some open questions and prospects of higher curvature nonlocal gravity on its way of achieving the UV completion.
Original languageEnglish
Title of host publicationHandbook of Quantum Gravity
EditorsCosimo Bambi, Leonarfo Modesto, Ilya Shapiro
PublisherSpringer Singapore
Pages1-38
Number of pages38
ISBN (Electronic)9789811930799
ISBN (Print)9789811930799
DOIs
Publication statusPublished - 16 Dec 2023

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