  We investigate features of the sterile neutrinos in the presence of a light
gauge boson $X^\mu$ that couples to the neutrino sector. The novel bounds on
the active-sterile neutrino mixings $| U_{\ell 4} |^2$, especially for tau
flavor ($l = \tau$), from various collider and fixed target experiments are
explored. Also, taking into account the additional decay channel of the sterile
neutrino into a light gauge boson ($\nu_4 \to \nu_\ell e^+ e^-$), we explore
and constrain a parameter space for low energy excess in neutrino oscillation
experiments.
