Vector Curvaton without Instabilities
  A vector curvaton model with a Maxwell kinetic term and varying kinetic
function and mass during inflation is studied. It is shown that, if light until
the end of inflation, the vector field can generate statistical anisotropy in
the curvature perturbation spectrum and bispectrum, with the latter being
predominantly anisotropic. If by the end of inflation the vector field becomes
heavy, then particle production is isotropic and the vector curvaton can alone
generate the curvature perturbation. The model does not suffer from
instabilities such as ghosts and is the only concrete model, to date, which can
produce the curvature perturbation without direct involvement of fundamental
scalar fields.
