A subclass of Gödel universes with closed timelike curves are exact vacuum solutions in nonlocal gravity for special nonlocal form factors.
Occurrence of exact $R^2$ inflation in non-local UV-complete gravity
4 Pith papers cite this work. Polarity classification is still indexing.
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abstract
The $R+R^2$, shortly named "$R^2$" ("Starobinsky") inflationary model, represents a fully consistent example of a one-parameter inflationary scenario. This model has a "graceful exit" from inflation and provides a mechanism for subsequent creation and final thermalization of the standard matter. Moreover, it produces a very good fit of the observed spectrum of primordial perturbations. In the present paper we show explicitly that the $R^2$ inflationary spacetime is an exact solution of a range of weakly non-local (quasi-polynomial) gravitational theories, which provide an ultraviolet completion of the $R^2$ theory. These theories are ghost-free, super-renormalizable or finite at quantum level, and perturbatively unitary. Their spectrum consists of the graviton and the scalaron that is responsible for driving the inflation. Notably, any further extension of the spectrum leads to propagating ghost degrees of freedom. We are aimed at presenting a detailed construction of such theories in the so called Weyl basis. Further, we give a special account to the cosmological implications of this theory by considering perturbations during inflation. The highlight of the non-local model is the prediction of a modified, in comparison to a local $R^2$ model, value for the ratio of tensor and scalar power spectra $r$, depending on the parameters of the theory. The relevant parameters are under control to be successfully confronted with existing observational data. Furthermore, the modified $r$ can surely meet future observational constraints.
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Fractional gravity yields stable de Sitter expansion and exact bouncing solutions driven by phantom (w < -1) or ghost (negative energy) fluids, with results independent of the form-factor representation.
Regular black holes in the bulk of quasi-topological gravity drive a de Sitter inflationary phase on the brane at small scales, with e-fold number set by the ratio of black hole radius to higher-curvature scale.
Specific choices of form factors in ghost-free infinite derivative gravity cancel all one-loop logarithmic UV divergences except the Gauss-Bonnet term and a surface term.
citing papers explorer
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Acausal exact vacuum solutions in nonlocal gravity
A subclass of Gödel universes with closed timelike curves are exact vacuum solutions in nonlocal gravity for special nonlocal form factors.
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Cosmology of fractional gravity
Fractional gravity yields stable de Sitter expansion and exact bouncing solutions driven by phantom (w < -1) or ghost (negative energy) fluids, with results independent of the form-factor representation.
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Cosmic Inflation From Regular Black Holes
Regular black holes in the bulk of quasi-topological gravity drive a de Sitter inflationary phase on the brane at small scales, with e-fold number set by the ratio of black hole radius to higher-curvature scale.
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Cancellation of UV divergences in ghost-free infinite derivative gravity
Specific choices of form factors in ghost-free infinite derivative gravity cancel all one-loop logarithmic UV divergences except the Gauss-Bonnet term and a surface term.