B_s^0 - \bar{B}_s^0 Mixing in Leptophobic Z^\prime Model
  Leptophobic Z^\prime gauge boson appears naturally in many grand unified theories, such as flipped SU(5) or string-inspired E_6 models. This elusive particle easily escapes the direct/indirect detections because it does not couple to charged leptons. However, it can generate flavor changing neutral current at tree level. In this letter, we show that the recently measured mass difference, \Delta m_s, in the B_s^0 -\bar{B}_s^0 system improves the previous bound of flavor changing effective coupling by about one order of magnitude, i.e irrespective of its phase, |U_{sb}^{Z^\prime}| \leq 0.036 for M_{Z^\prime} = 700 GeV, and |U_{sb}^{Z^\prime}| \leq 0.051 for M_{Z^\prime} = 1 TeV. 
Seungwon Baek, Jong Hun Jeon, and C.S. Kim (Yonsei U.)