  Braneworld inflation is a phenomenology related to string theory that
describes high-energy modifications to general relativistic inflation. The
observable universe is a braneworld embedded in 5-dimensional anti de Sitter
spacetime. Whe the 5-dimensional action is Einstein-Hilbert, we have a
Randall-Sundrum type braneworld. The amplitude of tensor and scalar
perturbations from inflation is strongly increased relative to the standard
results, although the ratio of tensor to scalar amplitudes still obeys the
standard consistency relation. If a Gauss-Bonnet term is included in the
action, as a high-energy correction motivated by string theory, we show that
there are important changes to the Randall-Sundrum case. We give an exact
analysis of the tensor perturbations. They satisfy the same wave equation and
have the same spectrum as in the Randall-Sundrum case, but the Gauss-Bonnet
change to the junction conditions leads to a modified amplitude of
gravitational waves. The amplitude is no longer monotonically increasing with
energy scale, but decreases asymptotically after an initial rise above the
standard level. Using an approximation that neglects bulk effects, we show that
the amplitude of scalar perturbations has a qualitatively similar behaviour to
the tensor amplitude. In addition, the tensor to scalar ratio breaks the
standard consistency relation.
