Explaining lepton-flavor non-universality and self-interacting dark matter with $$L_\mu -L_\tau $$ L μ - L τ

Abstract

Abstract Experimental hints for lepton-flavor universality violation in the muon’s magnetic moment as well as neutral- and charged-current B-meson decays require Standard-Model extensions by particles such as leptoquarks that generically lead to unacceptably fast rates of charged lepton flavor violation and proton decay. We propose a model based on a gauged $$U(1)_{L_\mu -L_\tau }$$ U ( 1 ) L μ - L τ that eliminates all these unwanted decays by symmetry rather than finetuning and efficiently explains $$(g-2)_\mu $$ ( g - 2 ) μ , $$R_{K^{(*)}}$$ R K ( ∗ ) , $$R_{D^{(*)}}$$ R D ( ∗ ) , and neutrino masses. The $$U(1)_{L_\mu -L_\tau }$$ U ( 1 ) L μ - L τ furthermore acts as a stabilizing symmetry for dark matter and the light $$Z'$$ Z ′ gauge boson mediates velocity-dependent dark-matter self-interactions that resolve the small-scale structure problems. Lastly, even the Hubble tension can be ameliorated via the light $$Z'$$ Z ′ contribution to the relativistic degrees of freedom.