$SO(10)\to SU(5)\times U(1{)}_{\chi }$ as the Origin of Dark Matter

In the decomposition of $SO(10)$ grand unification to $SU(5) \times U(1)_\chi$, two desirable features are obtained with the addition of one colored fermion octet $\mathrm{\Omega }$, one electroweak fermion triplet $\mathrm{\Sigma }$ and one complex scalar triplet $S$ to the particle content of the standard model with two Higgs doublets. They are (1) gauge coupling unification of $SU(3)_C \times SU(2)_L \times U(1)_Y$to$SU(5)$, and (2) the automatic (predestined) emergence of dark matter, i.e. $\mathrm{\Omega }$, $\mathrm{\Sigma }$ and $S$, with dark parity given by $(-1{)}^{Q_{\chi }+2j}$. It suggests that $U(1{)}_{\chi }$ may well be the underlying symmetry of the dark sector.