The GeV-scale dark matter with B-L asymmetry

One of important properties of dark matter is its stability. The U(1)$_{\rm B-L}$ gauge symmetry is the most attractive symmetry to guarantee the stability. Though the symmetry is expected to be broken at very high energy scale to account for tiny neutrino masses through the seesaw mechanism, the residual discrete symmetry of U(1)$_{\rm B-L}$ can stabilize the dark matter naturally. We prove that, when there is new physics connecting B$-$L charges of dark matter and standard model particles at the scale between the electroweak and the U(1)$_{\rm B-L}$ breaking, the mass of dark matter is definitely predicted to be (5--7)/$Q_{\rm DM}$ GeV ($Q_{DM}$ is the B$-$L charge of dark matter) independent not only of details of the new physics but also of its energy scale. We also show two attractive examples. First one is the scalar dark matter with the B$-$L charge of one, which turns out to be very consistent with current CoGeNT results. Another one is the fermionic dark matter having the B$-$L charge of one third, which is also attractive from the viewpoint of model building.