Cosmological constant in F(R) supergravity
  A cosmological constant in the regime of low space-time curvature is calculated in the recently proposed version of F(R) supergravity with a generic cubic function F. The F(R) supergravity is the N=1 supersymmetric extension of f(R) gravity. The cubic model is known to successfully describe a chaotic (slow-roll) inflation in the regime of high space-time curvature. We find that a simple extension of the same model allows a positive cosmological constant in the regime of low space-time curvature. The inflaton superfield in F(R) supergravity (like inflaton in f(R) gravity) violates the Strong Energy Condition and thus breaks the restriction of the standard supergravity (with usual matter) that can only have either a negative or vanishing cosmological constant. 
Sergei V. Ketov and Natsuki Watanabe
hep-th gr-qc