We study in detail the possibility that the flat directions of the Minimal Supersymmetric Standard Model ( MSSM ) could act as a curvaton and generate the observed adiabatic density perturbations .
For that the flat direction energy density has to dominate the Universe at the time when it decays .
We point out that this is not possible if the inflaton decays into MSSM degrees of freedom .
If the inflaton is completely in the hidden sector , its decay products do not couple to the flat direction , and the flat direction curvaton can dominate the energy density .
This requires the absence of a Hubble-induced mass for the curvaton , e.g .
by virtue of the Heisenberg symmetry .
In the case of hidden radiation , n = 9 is the only admissible direction ; for other hidden equations of state , directions with lower n may also dominate .
We show that the MSSM curvaton is further constrained severely by the damping of the fluctuations , and as an example , demonstrate that in no-scale supergravity it would fragment into Q 
balls rather than decay .
Damping of fluctuations can be avoided by an initial condition , which for the n = 9 direction would require an initial curvaton amplitude of \sim 10 ^ { -2 } M _ { p } , thereby providing a working example of the MSSM flat direction curvaton .