Generic f(R) theories and classicality of their scalarons
  We study quantum stability bound on the mass of scalaron in generic theories of $f(R)$ gravity. We show that in these scenarios, the scalaron mass increases faster with local density of the environment than one loop quantum correction to it thereby leading to violation of quantum bound on the chameleon mass. The introduction of quadratic curvature corrections in the action are shown to stabilize the model. 
R. Gannouji, M. Sami, I. Thongkool
hep-th gr-qc hep-ph