  We present a curvaton model from type IIB string theory compactified on a
warped throat with approximate isometries. Considering an (anti-)D3-brane
sitting at the throat tip as a prototype standard model brane, we show that the
brane's position in the isometry directions can play the role of curvatons. The
basic picture is that the fluctuations of the (anti-)D3-brane in the angular
isometry directions during inflation eventually turns into the primordial
curvature perturbations, and subsequently the brane's oscillation excites other
open string modes on the brane and reheat the universe. We find in the explicit
case of the KS throat that a wide range of parameters allows a consistent
curvaton scenario. It is also shown that the oscillations of branes at throat
tips are capable of producing large non-Gaussianity, either through curvature
or isocurvature perturbations. Since such setups naturally arise in warped
(multi-)throat compactifications and are constrained by observational data, the
model can provide tests for compactification scenarios. This work gives an
explicit example of string theory providing light fields for generating
curvature perturbations. Such mechanisms free the inflaton from being
responsible for the perturbations, thus open up new possibilities for inflation
models.
