Tensor Perturbations from Brane-World Inflation with Curvature Effects
  The brane-world scenario provides an intriguing possibility to explore the
phenomenological cosmology implied by string/M theory. In this paper, we
consider a modified Randall-Sundrum single brane model with two natural
generalizations: a Gauss-Bonnet term in the five-dimensional bulk action as
well as an induced gravity term in the four-dimensional brane action, which are
the leading-order corrections to the Randall-Sundrum model. We study the
influence of these combined effects on the evolution of the primordial
gravitational waves generated during an extreme slow-roll inflation on the
brane. The background, for the early inflationary era, is then modeled through
a de Sitter brane embedded within an anti-de Sitter bulk. In this framework, we
show that both effects tend to suppress the Randall-Sundrum enhancement of the
amplitude of the tensor perturbations at relatively high energies. Moreover,
the Gauss-Bonnet effect, relative to standard general relativity, will abruptly
enhance the tensor-to-scalar ratio and break the standard consistency relation
at high energies, which cannot be evaded by invoking the induced gravity
effect, even though the induced gravity strength would mildly counterbalance
these significant changes at high energies. We note that the brane-world model
with or without the induced gravity effect fulfills the consistency relation.
Finally, we discuss some implications of the observational constraints.
