  There are only two viable low-energy $E_6$ subgroups: $SU(3)_C \times SU(2)_L
\times U(1)_Y \times U(1)_N$ or $SU(3)_C \times SU(2)_L \times SU(2)'_R \times
U(1)_{Y_L + Y'_R}$, which would not erase any preexisting lepton asymmetry of
the Universe that may have been created by the decay of heavy singlet
(right-handed) neutrinos or any other mechanism. They are also the two most
favored $E_6$ subgroups from a recent analysis of present neutral-current data.
We study details of the leptogenesis, as well as some salient experimental
signatures of the two models.
