Slow-roll inflation with a Gauss-Bonnet correction
  We consider slow-roll inflation for a single scalar field with an arbitrary
potential and an arbitrary nonminimal coupling to the Gauss-Bonnet term. By
introducing a combined hierarchy of Hubble and Gauss-Bonnet flow functions, we
analytically derive the power spectra of scalar and tensor perturbations. The
standard consistency relation between the tensor-to-scalar ratio and the
spectral index of tensor perturbations is broken. We apply this formalism to a
specific model with a monomial potential and an inverse monomial Gauss-Bonnet
coupling and constrain it by the 7-year Wilkinson Microwave Anisotropy Probe
data. The Gauss-Bonnet term with a positive (or negative) coupling may lead to
a reduction (or enhancement) of the tensor-to-scalar ratio and hence may revive
the quartic potential ruled out by recent cosmological data.
