B Anomalies and Dark Matter in an L_μ-L_τ Model with General Kinetic Mixing

We revisit the $L_\mu - L_\tau$ extension of the Standard Model that can simultaneously address anomalies in semileptonic $B$ meson decays and the nature of dark matter (DM). In the region favored by the $B$ anomalies, this scenario is excluded by a combination of low-energy flavor constraints and stringent DM direct detection constraints if the kinetic mixing between $Z^\prime$ gauge boson and the photon vanishes at high energy scales, since this leads to a sizable coupling between DM and the SM in low-momentum scattering processes. However, this is no longer the case if the kinetic mixing vanishes at low energy scales instead. In this scenario, the low-momentum DM scattering rate can be suppressed and constraints from direct detection experiments can be substantially relaxed. As a result, we find a re-opening of the region of parameter space where the $B$ anomalies and DM can be simultaneously explained.