Explaining dark matter and B decay anomalies with an Lμ− Lτmodel

Abstract

We present a dark sector model based on gauging the Lμ− Lτsymmetry that addresses anomalies in b → sμ+μ−decays and that features a particle dark matter candidate. The dark matter particle candidate is a vector-like Dirac fermion coupled to the Z′ gauge boson of the Lμ− Lτsymmetry. We compute the dark matter thermal relic density, its pair-annihilation cross section, and the loop-suppressed dark matter-nucleon scattering cross section, and compare our predictions with current and future experimental results. We demonstrate that after taking into account bounds from Bsmeson oscillations, dark matter direct detection, and the CMB, the model is highly predictive: B physics anomalies and a viable particle dark matter candidate, with a mass of ∼ (5 − 23) GeV, can be accommodated only in a tightly-constrained region of parameter space, with sharp predictions for future experimental tests. The viable region of parameter space expands if the dark matter is allowed to have Lμ− Lτcharges that are smaller than those of the SM leptons.