  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.
