Abstract
We discuss fermionic dark matter in non-supersymmetric E6 Grand Unification. The fundamental representation of E6 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 E6 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 3 · 109 GeV ≲ mDM ≲ 1 · 1013 GeV for our E6 dark matter candidate, which is within the reach of next-generation direct detection experiments.
Highlights
That really sets E6 apart from all other popular GUT groups: for example, SU(5) is part of the infinite SU(N ) family, SO(10) of the infinite SO(N ) family and “describing nature by a group taken from an infinite family does raise an obvious question — why this group and not another?” [16]
We start by presenting the particle content of our E6 model and discuss under which conditions the lightest exotic fermion is stable through a remnant symmetry
We have shown that E6 unification incorporates an inherent, viable dark matter candidate that could be detected in the near future
Summary
The particle content of E6 representations depends on the embedding of the standard model gauge group GSM ≡ SU(3)C × SU(2)L × U(1)Y in E6. The fermions (all taken to be left-handed) are contained in the fundamental 27-dimensional representation Ψ of E6. The particle content of the fermionic 27, for our standard model embedding, is best understood by considering the decomposition under SO(10). Ψ16 contains the 15 standard model fermions of one generation plus the charge conjugated right-handed neutrino νRc. The fermions in the 10 are vector-like, because the 10 is a selfconjugate SO(10) representation. The fermions in the 10 are vector-like, because the 10 is a selfconjugate SO(10) representation It contains an exotic down-type quark D plus an exotic lepton doublet (NE, E).
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