Dirac right-handed neutrinos in a U(1)_{B-L} Z' portal model produce observable ΔN_eff that, together with direct/indirect detection and collider bounds, carves out testable WIMP and FIMP dark-matter regions.
Light $Z^\prime$ and Dark Matter from U(1)$_X$ Gauge Symmetry
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abstract
We consider a U(1)$_X$ gauge symmetry extension of the Standard Model (SM) with a $Z^\prime$-portal Majorana fermion dark matter that allows for a relatively light gauge boson $Z^\prime$ with mass of 10 MeV$-$ a few GeV and a much heavier dark matter through the freeze-in mechanism. In a second scenario the roles are reversed, and the dark matter mass, in the keV range or so, lies well below the $Z^\prime$ mass, say, $\sim 1$ GeV. We outline the parameter space that can be explored for these two scenarios at the future Lifetime Frontier experiments including Belle-II, FASER, LDMX and SHiP.
years
2026 2representative citing papers
NA64 sets improved upper limits on g_{B-L} for sub-GeV Z' using 9.4e11 electrons on target, exceeding prior neutrino-scattering bounds in the unbroken U(1)_{B-L} scenario.
citing papers explorer
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$Z^\prime$ Portal Dark Matter with Observable $\Delta N_{\rm eff}$
Dirac right-handed neutrinos in a U(1)_{B-L} Z' portal model produce observable ΔN_eff that, together with direct/indirect detection and collider bounds, carves out testable WIMP and FIMP dark-matter regions.
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Improved limits on a new $Z'$ in $B-L$ scenarios with the NA64 experiment at CERN
NA64 sets improved upper limits on g_{B-L} for sub-GeV Z' using 9.4e11 electrons on target, exceeding prior neutrino-scattering bounds in the unbroken U(1)_{B-L} scenario.