  Though not completely a surprise according to the standard model and existing
indirect constraints, the Higgs-like particle, h, of mass around 125 GeV
recently observed at the LHC may offer an additional window to physics beyond
the standard model. In particular, its decay pattern can be modified by the
existence of new particles. One of the popular scenarios involves a Z' boson
associated with an extra Abelian gauge group. In this study, we explore the
potential effects of such a boson with family-nonuniversal couplings on the
leptonic decays of h, both flavor-conserving and flavor-changing. For current
constraints, we take into account leptonic decays at the Z pole, LEP II
scattering data, limits on various flavor-changing lepton transitions, and
lepton magnetic dipole moments. Adopting a model-independent approach and
assuming that the Z' has negligible mixing with the Z boson, we find that
present data allow the Z' effects to reach a few percent or higher on h decays
into a pair of leptons. Future measurements on h at the LHC or a linear
collider can therefore detect the Z' contributions or impose further
constraints on its couplings. We also consider Z'-mediated four-lepton decays
of the Z and W bosons.
