Axion Gauge Field Inflation and Gravitational Leptogenesis: A Lower
  Bound on B Modes from the Matter-Antimatter Asymmetry of the Universe
  We present a toy model of an axion gauge field inflation scenario that yields
viable density and gravitational wave spectra. The scenario consists of an
axionic inflaton in a steep potential that is effectively flattened by a
coupling to a collection of non-Abelian gauge fields. The model predicts a
blue-tilted gravitational wave spectrum that is dominated by one circular
polarization, resulting in unique observational targets for cosmic microwave
background and gravitational wave experiments. The handedness of the
gravitational wave spectrum is incorporated in a model of leptogenesis through
the axial-gravitational anomaly; assuming electroweak sphaeleron processes
convert the lepton asymmetry into baryons, we predict an approximate lower
bound on the tensor-to-scalar ratio r ~ 3-4e-2 for models that also explain the
matter-antimatter asymmetry of the Universe.
