We recall the argument based both on Dirac's square root procedure and anintrinsic Pauli principle that sterile fundamental fermions with spin 1/2(sterinos) ought to appear in Nature in two or three generations, while theStandard Model leptons and quarks are forced to develop three generations.Then, sterinos in two or three generations, if stable, lead to the cold darkmatter in two or three species, when the thermal freeze-out mechanism worksproperly. If they are stable only in their lowest generation, the so calledexciting cold dark matter may be formed.
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