We build a realistic model of curvaton cosmology, in which the energy content is described by radiation, WIMP dark matter, and a curvaton component. We calculate the curvature and isocurvature perturbations, allowing for arbitrary initial density perturbations in all fluids, following all species and their perturbations from the onset of dark matter freeze-out onto well after curvaton decay. We provide detailed numerical evaluations as well as analytical formulas which agree well with the latter. We find that substantial isocurvature perturbations, as measured relatively to the total curvature perturbation, can be produced even if the curvaton energy density is well underdominant when it decays; high precision measurements of cosmic microwave background anisotropies may thus open a window on underdominant decoupled species in the prenucleosynthesis early Universe. We also find that, in a large part of parameter space, curvaton decay produces enough dark matter particles to restore WIMP annihilations, leading to the partial erasure of any preexisting dark matter–radiation isocurvature perturbation.

• Received 1 December 2006

DOI:https://doi.org/10.1103/PhysRevD.75.063504