The Dark Z and Charged Higgs Decay

Understand

If there is an additional U(1) symmetry under which Standard Model particles are singlets, then there can be mixing between the additional gauge boson and the hypercharge gauge boson.

• This can lead to a very light, but weakly coupled "dark" gauge boson, the $Z_d$, with a mass of O(1) GeV.
• If the $Z_d$ gets its mass entirely from a Higgs singlet, it is called a dark photon; whereas if there is a second Higgs doublet, it is called a dark Z.
• We look at charged Higgs boson decays in the dark Z model.