Searching for signatures of $E_{\rm 6}$
  The grand unified group $E_6$~is a predictive scheme for physics beyond the standard model (SM). It offers the possibility of extra $Z$ bosons, new vector-like fermions, sterile neutrinos, and neutral scalars in addition to the SM Higgs boson. Some previous discussions of these features are updated and extended. Their relevance to present searches at the CERN Large Hadron Collider and in patterns of neutrino masses is noted. Addition of a small set of scalar bosons at the TeV scale permits gauge unification near a scale of $10^{16}$ GeV, and leads to bounds on masses of particles beyond those in the standard model. 
Aniket Joglekar, Jonathan L. Rosner
hep-ph