Singlet fermionic dark matter with dark Z

Abstract

We present a fermionic dark matter model mediated by the hidden gauge boson. We assume the QED-like hidden sector which consists of a Dirac fermion and U(1)X gauge symmetry, and introduce an additional scalar electroweak doublet field with the U(1)X charge as a mediator. The hidden U(1)X symmetry is spontaneously broken by the electroweak symmetry breaking and there exists a massive extra neutral gauge boson in this model which is the mediator between the hidden and visible sectors. Due to the U(1)X charge, the additional scalar doublet does not couple to the Standard Model fermions, which leads to the Higgs sector of type I two Higgs doublet model. The new gauge boson couples to the Standard Model fermions with couplings proportional to those of the ordinary Z boson but very suppressed, thus we call it the dark Z boson. We study the phenomenology of the dark Z boson and the Higgs sector, and show the hidden fermion can be the dark matter candidate.