Flavour-changing neutral currents and leptophobic Z′ gauge bosons

Leptophobic Z′ gauge bosons can appear in models with an E6 gauge symmetry. We show that flavour-changing neutral currents can be generated in some of these models due to the mixing of the ordinary dR, sR and bR quark fields with the exotic hR. Because the Z′ does not couple to charged leptons, the constraints on the flavour-changing couplings UZ′db and UZ′sb are relatively weak. Indeed, B0q–B̄ 0q mixing (q=d,s) can be dominated by Z′ exchange, which will affect CP-violating rate asymmetries in B decays. Rare hadronic B decays can also be affected, while decays involving charged leptons will be unchanged.