Leptophobic Z′ in heterotic-string derived models

The CDF Collaborationʼs recent observation of an excess of events in the Wjj channel may be attributed to a new Abelian vector boson with suppressed couplings to leptons. While D0 finds no evidence of an excess, the CDF data provide an opportunity to revisit an old result on leptophobic Z′ in heterotic-string derived models. We re-examine the conditions for the existence of a leptophobic U(1) symmetry, which arises from a combination of the U(1)B−L symmetry and the horizontal flavour symmetries, to form a universal U(1) symmetry. While the conditions for the existence of a leptophobic combination are not generic, we show that the left-right symmetric free fermionic heterotic-string models also admit a leptophobic combination. In some cases the leptophobic U(1) is augmented by the enhancement of the colour group, along the lines of models proposed by Foot and Hernandez.