Speaker
Description
A new $U(1)_X$ gauge boson field X can have renormalizable kinetic mixing with the standard model (SM) $U(1)_Y$ gauge boson field Y. Besides the dark photon kinetic mixing $\sigma$, there could be mass mixing by introducing the additional Higgs doublet with vev engaging in $U(1)_X$ and electroweak symmetry breaking simultaneously. The Z boson interaction with SM tau lepton is modified by defining the mixing ratio parameter $\epsilon$, which shows the magnitude of the mass and kinetic mixing of dark photon. We investigate the Z boson phenomenology of dark photon model with both the kinetic mixing and mass mixing. The allowed parameter region is obtained by analyzing these constraints from the vector and axial-vector couplings $g_{V,A}^\tau$, the decay branching ratio $Br(Z\to \tau^- \tau^+)$ and tau lepton polarization in $Z\to \tau^-\tau^+$. We found that the mixing ratio plays important role in the Z boson features by choosing different $\epsilon$ values.
Further, we attempt to find the common regions to satisfy these above four bounds for $m_X>m_Z$ and $m_X
