Observational Viability and Stability of Nonlocal Cosmology
  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.
