$\gamma$ gravity: Steepness control
  We investigate a simple generalization of the metric exponential $f(R)$
gravity theory that is cosmologically viable and compatible with solar system
tests of gravity. We show that, as compared to other viable $f(R)$ theories,
its steep dependence on the Ricci scalar $R$ facilitates agreement with
structure constraints, opening the possibility of $f(R)$ models with
equation-of-state parameter that could be differentiated from a cosmological
constant ($w_{de}=-1$) with future surveys at both background and perturbative
levels.
