Self–Interacting Dark Matter from the Hidden Heterotic–String Sector

It has been suggested recently that self–interacting dark matter fits better the observational characteristics of galaxy dynamics. We propose that the self–interacting dark matter is composed from the glueballs of the hidden sector non–Abelian gauge group, while the hidden matter states exist in vector–like representation and decouple from the light spectrum. It is shown that these glueballs are semi–stable with the life–time larger than the present age of the Universe, if their mass is 1 GeV or less. The constraint on their abundance today suggests that the energy was stored in the hidden sector soon after inflation. This imposes an upper limit on the reheating temperature. We further study the naturalness of this scenario in the context of the free–fermionic string models and point out a class of such models where the self–interacting dark matter from the hidden sector is indeed plausible.