  Simple curvaton models can generate a mixture of of correlated primordial
adiabatic and isocurvature perturbations. The baryon and cold dark matter
isocurvature modes differ only by an observationally null mode in which the two
perturbations almost exactly compensate, and therefore have proportional
effects at linear order. We discuss the CMB anisotropy in general mixed models,
and give a simple approximate analytic result for the large scale CMB
anisotropy. Working numerically we use the latest WMAP observations and a
variety of other data to constrain the curvaton model. We find that models with
an isocurvature contribution are not favored relative to simple purely
adiabatic models. However a significant primordial totally correlated baryon
isocurvature perturbation is not ruled out. Certain classes of curvaton model
are thereby ruled out, other classes predict enough non-Gaussianity to be
detectable by the Planck satellite. In the appendices we review the relevant
equations in the covariant formulation and give series solutions for the
radiation dominated era.
