Dark Matter Constraints on Low Mass and Weakly Coupled B-L Gauge Boson

Understand

We investigate constraints on the new $B-L$ gauge boson ($Z_{BL}$) mass and coupling ($g_{BL}$) in a $U(1)_{B-L}$ extension of the standard model (SM) with an SM singlet Dirac fermion ($\zeta$) as dark matter (DM).

• The DM particle $\zeta$ has an arbitrary $B-L$ charge $Q$ chosen to guarantee its stability.
• We focus on the small $Z_{BL}$ mass and small $g_{BL}$ regions of the model, and find new constraints for the cases where the DM relic abundance arises from thermal freeze-out as well as freeze-in mechanisms.
• In the thermal freeze-out case, the DM coupling is given by $g_{\zeta}\equiv g_{BL}Q\simeq0.016\sqrt{m_\zeta[{\rm GeV}]}$ to reproduce the observed DM relic density and $g_{BL}\geq 2.7 \times 10^{-8} \sqrt{m_\zeta[{\rm GeV}]}$ for the DM particle to be in thermal equilibrium prior to freeze-out.