Cosmic Density Perturbations from Late-Decaying Scalar Condensations

Abstract

We study the cosmic density perturbations induced from fluctuation of the amplitude of late-decaying scalar condensations (called ϕ) in the scenario where the scalar field ϕonce dominates the universe. In such a scenario, the cosmic microwave background (CMB) radiation originates to decay products of the scalar condensation and hence its anisotropy is affected by the fluctuation of ϕ. It is shown that the present cosmic density perturbations can be dominantly induced from the primordial fluctuation of ϕ, not from the fluctuation of the inflaton field. This scenario may change constraints on the source of the density perturbations, like inflation. In addition, a correlated mixture of adiabatic and isocurvature perturbations may arise in such a scenario; possible signals in the CMB power spectrum are discussed. We also show that the simplest scenario of generating the cosmic density perturbations only from the primordial fluctuation of ϕ(i.e., so-called ``curvaton'' scenario) is severely constrained by the current measurements of the CMB angular power spectrum if correlated mixture of the adiabatic and isocurvature perturbations are generated.