Dark Matter in $E_6$ Grand Unification

We discuss fermionic dark matter in non-supersymmetric $E_6$ Grand Unification. The fundamental representation of $E_6$ contains, in addition to the standard model fermions, exotic fermions and we argue that one of them is a viable, interesting dark matter candidate. Its stability is guaranteed by a discrete remnant symmetry, which is an unbroken subgroup of the $E_6$ gauge symmetry. We compute the symmetry breaking scales and the effect of possible threshold corrections by solving the renormalization group equations numerically after imposing gauge coupling unification. Since the Yukawa couplings of the exotic and the standard model fermions have a common origin, the mass of the dark matter particles is constrained. We find a mass range of ${10^{8} \text{ GeV} \lesssim m_{DM} \lesssim 10^{12} \text{ GeV}}$ for our $E_6$ dark matter candidate, which is within the reach of next-generation direct detection experiments.