## Harmony in g flat – maintaining unitarity under relevant deformations of the Einstein-Hilbert action

May 27, 2011

In this Letter the authors consider generic relevant deformations of the Einstein-Hilbert action on arbitrary backgrounds at the linear level. Explicit results are shown for Friedmann-Robertson-Walker (FRW) spacetimes. They analyze the classical and quantum stability of the free theory,’ which is a necessary prerequisite before completing the corresponding deformations at the nonlinear level.