  We present a model of inflation in which the inflaton field is charged under
a triplet of $U(1)$ gauge fields. The model enjoys an internal $O(3)$ symmetry
supporting the isotropic FRW solution. With an appropriate coupling between the
gauge fields and the inflaton field, the system reaches an attractor regime in
which the gauge fields furnish a small constant fraction of the total energy
density. We decompose the scalar perturbations into the adiabatic and entropy
modes and calculate the contributions of the gauge fields into the curvature
perturbations power spectrum. We also calculate the entropy power spectrum and
the adiabatic-entropy cross correlation. In addition to the metric tensor
perturbations, there are tensor perturbations associated with the gauge field
perturbations which are coupled to metric tensor perturbations. We show that
the correction in primordial gravitational tensor power spectrum induced from
the matter tensor perturbation is a sensitive function of the gauge coupling.
