Marginally Deformed Starobinsky Gravity

Preprint number: CP3-Origins-2014-13 DNRF90 and DIAS-2014-13
Authors: Alessandro Codello (CP3-Origins & DIAS), Jakob Joergensen (CP3-Origins & DIAS), Francesco Sannino (CP3-Origins & DIAS), and Ole Svendsen (CP3-Origins & DIAS)
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We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form R2(1 −α), with R the Ricci scalar and α 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 α. Furthermore we argue, that within this framework, the tensor modes probe theories of grand unification with a large scalar field content.