Z ′ -induced FCNC decays of top, beauty, and strange quarks

Anomalous b[arrowright]s transitions from LHCb data may suggest a new massive gauge boson Z' that couples to the left-handed b[arrowright]s current, which in turn implies a coupling to the t[arrowright]c current. In this paper, we study flavor-changing neutral current (FCNC) decays of the top quark induced by a Z' boson, namely t[arrowright]cZ', based on a model of the gauged L sub([mu])-L sub([tau]) symmetry (the difference between the muon and tauon numbers) with vectorlike quarks, which was introduced to explain the anomalous LHCb data. We illustrate that searching for t[arrowright]cZ' via Z'[arrowright][mu] super(+)[mu] super(-) with LHC Run 1 data can probe a parameter region that is unexplored by B physics for a Z' mass of around [vartheta](10)GeV or greater. We further extend the model to a very light Z' with mass below 400 MeV, which is motivated by the muon g-2 anomaly. Taking rare B and K meson decay data into account, we give upper limits on the t[arrowright]cZ' branching ratio for the light Z' case, and discuss about its observability at the LHC. We also scrutinize the possibility that the decay K sub(L)arrowright][pi] super(0)Z' with Z'[arrowright][nu][nu] may lead to an apparent violation of the usual Grossman-Nir bound of [beta](K sub(L)arrowright][pi] super(0)[nu][nu])