We show that the recently suggested explanations of cosmic acceleration by
the modification of gravity at small curvature suffer violent instabilities and
strongly disagree with the known properties of gravitational interactions.Comment: 4 pages, no figure, revised version (one footnote added
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.