A Light $Z'$ Boson
  A model of a light $Z'$ boson based on gauged $L_\mu - L_\tau$ $U(1)$ symmetry is constructed. The $Z'$ boson mass is constrained to be in the range of 0.8 to 1 GeV from Z and $Z'$ mass relation, g-2 of muon, and tau decays. The two body decay $\tau \rightarrow \mu Z'$ is possible. This will provide a striking signature to test the model. Talk presented at the Eighth Meeting of the American Physical Society, Division of Particles and Fields (DPF'94), Albuqurque, New Mexico, August 2-6, 1994. 
Xiao-Gang He