Cosmic density perturbations from late-decaying scalar condensations

We study the cosmic density perturbations induced from the fluctuation of the amplitude of late-decaying scalar condensations (called $\phi )$ in the scenario where the scalar field $\phi$ once 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 $\phi .$ It is shown that the present cosmic density perturbations can be dominantly induced from the primordial fluctuation of $\phi ,$ 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 $\phi$ (i.e., the so-called “curvaton” scenario) is severely constrained by the current measurements of the CMB angular power spectrum if the correlated mixture of the adiabatic and isocurvature perturbations are generated.