Power spectra from an inflaton coupled to the Gauss-Bonnet term
  We consider power-law inflation with a Gauss-Bonnet correction inspired by
string theory. We analyze the stability of cosmological perturbations and
obtain the allowed parameter space. We find that for GB-dominated inflation
ultra-violet instabilities of either scalar or tensor perturbations show up on
small scales. The Gauss-Bonnet correction with a positive (or negative)
coupling may lead to a reduction (or enhancement) of the tensor-to-scalar ratio
in the potential-dominated case. We place tight constraints on the model
parameters by making use of the WMAP 5-year data.
