The Muonic Portal to Vector Dark Matter:connecting precision muon physics, cosmology, and colliders

Abstract

We present a comprehensive study of the Muonic Portal to Vector Dark Matter (MPVDM), a minimal extension of the Standard Model featuring a new $SU(2)_D$ gauge symmetry and vector-like muons that mediate interactions between the dark sector and the muon sector. We show that the MPVDM can simultaneously reproduce the observed dark matter relic abundance and accommodate scenarios consistent with the current experimental determination of the muon anomalous magnetic moment, $(g-2)_\mu$, as well as scenarios allowing for a non-zero new physics contribution to $(g-2)_\mu$. One of the key results of this work is the identification of a generic off-resonance velocity-suppression mechanism that allows light ($\lesssim 1$ GeV) vector dark matter to evade stringent CMB constraints near $2m_{\mathrm{DM}}\simeq m_{H_D}$. A five-dimensional parameter scan combining cosmological, collider, and precision constraints shows that scenarios admitting a non-zero contribution to $(g-2)_\mu$ favour sub-GeV dark matter realised near the scalar resonance with a dark gauge coupling $g_D\!\sim\!10^{-3}$ and TeV-scale vector-like muons, while scenarios consistent with a Standard-Model-like $(g-2)_\mu$ allow a broad viable dark matter mass range from sub-GeV to multi-TeV. By recasting ATLAS and CMS searches for $\mu^+\mu^-$ final states with missing transverse energy, we derive a lower bound of approximately 850~GeV on the vector-like muon masses. We further identify distinctive multi-lepton collider signatures, including six-, eight-, and ten-muon final states as well as mixed muon--electron topologies with displaced electron pairs, providing striking and well-motivated targets for searches at the LHC and future colliders.