Observational Viability and Stability of Nonlocal Cosmology

TL;DR

This paper demonstrates that certain nonlocal gravity models can explain cosmic acceleration without dark energy, remain consistent with local gravity tests, and are stable and ghost-free, unlike their localized counterparts.

Contribution

It introduces a class of nonlocal gravity models that are both observationally viable and stable, avoiding ghosts and preserving general relativity predictions for bound systems.

Findings

Models do not alter gravitationally bound systems' predictions.

Models are stable and ghost-free.

Nonlocal modifications do not introduce additional excitations.

Abstract

We show that a class of nonlocal gravity models, proposed to explain current cosmic acceleration without dark energy, passes two major tests: First, they can be defined so as not to alter the, observationally correct, general relativity predictions for gravitationally bound systems. Second, they are stable, ghost-free, with no additional excitations beyond those of general relativity. In this they differ from their, ghostful, localized versions. The systems' initial value constraints are the same as in general relativity, and our nonlocal modifications never convert the original gravitons into ghosts.