Dark matter interactions from an extra U(1) gauge symmetry with kinetic mixing and Higgs charge* *Supported by the National Natural Science Foundation of China (12135014)

Abstract

We investigate fermionic dark matter interactions with standard model particles from an additional gauge symmetry, assuming kinetic mixing between the and gauge fields as well as a nonzero charge of the Higgs doublet. To ensure gauge-invariant Yukawa interactions and the cancellation of gauge anomalies, standard model fermions are assigned Y-sequential charges proportional to the Higgs charge. Although the Higgs charge should be small owing to collider constraints, it is useful to decrease the effective cross section of dark matter scattering off nucleons by two orders of magnitude to easily evade direct detection bounds. After performing numerical scans in the parameter space, we find that the introduction of the Higgs charge can also enhance the dark matter relic density by at least two orders of magnitude. In the case where the resonance effect is important for dark matter freeze-out, when the observed relic density and direct detection constraints are tangled, the Higgs charge can expand physical windows to some extent by relieving the tension between the relic density and direct detection.