  Multi-spinor fields which behave as triple-tensor products of the Dirac
spinors and form reducible representations of the Lorentz group describe three
families of ordinary quarks and leptons in the visible sector and an additional
family of exotic dark quarks and leptons in the dark sector of the Universe.
Apart from the ordinary set of the gauge and Higgs fields in the visible
sector, another set of gauge and Higgs fields belonging to the dark sector are
assumed to exist. Two sectors possess channels of communication through gravity
and a bi-quadratic interaction between the two types of Higgs fields. A
candidate for the main component of the dark matter is a stable dark hadron
with spin 3/2, and the upper limit of its mass is estimated to be 15.1
GeV/c$^2$.
