A viability criterion for modified gravity with an extra force
arXiv:0710.1291 · doi:10.1103/PhysRevD.76.127501
Abstract
A recently proposed theory of modified gravity with an explicit ``anomalous'' coupling of the Ricci curvature to matter is discussed, and an inequality is derived which expresses a necessary and sufficient condition to avoid the notorius Dolgov-Kawasaki instability.
4 latex pages, to appear in Phys. Rev. D