• A SM gauge invariant curvaton: MSSM provides gauge invariant curvaton candidates [134–136, 823–825, 833, 840, 841, 851–854], which can decay into MSSM degrees of freedom directly. In this case the curvaton must ensure its longevity, and its dominance at the time of decay. If the inflaton decay products are of MSSM/SM like quanta, then they can interact with the MSSM curvaton and can possibly destroy its coherence and longevity [136, 833]. The advantage of an MSSM curvaton is that the couplings are that of the SM, therefore, predictions are robust. B. Cosmological constraints on a curvaton scenario The main observable constraints for a curvaton scenario are: (1) isocurvature perturba- tions, and (2) primordial non-Gaussianity. The isocurvature perturbations are created when the curvaton fail to dominate the energy density while decaying and the curvaton decay proucts fail to thermalize with that of the inflaton decay products. There are potentially well motivated isocurvature perturbations one can create, CDM [131, 229–231, 837, 855], baryon isocurvature perturbations [128, 131, 856–861], neutrino isocurvature perturbations were also considered in [131] $^{105}$. For a conserved number density δn$_{i}$ = 0, where i corresponds to baryons or CDM, the entropy perturbation is given by [131, 251] S i = 3 ( ζ$_{i}$ − ζ ) , (442) where ζ is the total curvature perturbations, and ζ$_{i}$ is the curvature perturbations in the i component. Recall that in a curvaton scenario the total curvature perturbations is given by; ζ = rζ$_{ϕ}$ , where r = ρ$_{ϕ}$/ρ$_{r}$ at the time of curvaton decay, and ρ$_{r}$ is the radiation energy density due to the inflaton decay products. Let us now imagine, when the curvaton decays either into baryons (need not be the SM baryons), or non-relativistic CDM, then ζ$_{i}$ = ζ$_{ϕ}$ = (1 /r ) ζ . Combining this fact, the 105 There is a way to avoid large isocurvature component provided the inflaton perturbations are subdominant during inflation, i.e. ( δρ/ρ )$_{inf}$ ≪ 10 − $^{5}$. This can be achieved very well in many inflationary models [831], but the curvaton perturbations can create the required level of perturbations even if they do not dominate the energy density while decaying. This can be possible for a curvaton potential discussed in Eq. (458) for specific choices of ( n, m$_{0}$ ), see Ref. [831]. 209