Marginally Deformed Starobinsky Gravity

Understand

We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form $R^{2(1 -\alpha)}$, with $R$ the Ricci scalar and $\alpha$ a positive parameter, smaller than one half, can account for the recent experimental observations by BICEP2 of primordial tensor modes.

• We also suggest natural microscopic (non) gravitational sources of these corrections and demonstrate that they lead generally to a nonzero and positive $\alpha$.
• Furthermore we argue, that within this framework, the tensor modes probe theories of grand unification with a large scalar field content.