We revisit the number-theory dark matter scenario where one of the light
chiral fermions required by the anomaly cancellation conditions of U(1)_{B-L}
explains dark matter. Focusing on some of the integer B-L charge assignments,
we explore a new region of the parameter space where there appear two light
fermions and the heavier one becomes a dark matter of mass O(10)keV or
O(10)MeV. The dark matter radiatively decays into neutrino and photon, which
can explain the tantalizing hint of the 3.55keV X-ray line excess.
Interestingly, the other light fermion can erase the AdS vacuum around the
neutrino mass scale in a compactification of the standard model to 3D. This
will make the standard model consistent with the AdS-WGC statement that stable
non-supersymmetric AdS vacua should be absent.Comment: 16 pages, 4 figure