Hint from the interfamily mass hierarchy: Two vectorlike families in the TeV range.

Two vector–like families QL,R = (U,D,N,E)L,R and Q ′ L,R = (U ,D, N , E)L,R with masses of order 1 TeV, one of which is a doublet of SU(2)L and the other a doublet of SU(2)R, have been predicted to exist, together with the three observed chiral families, in the context of a viable and economical SUSY preon model. The model itself possesses many attractive features which include explanations of the origins of (i) diverse mass–scales, (ii) family–replication, (iii) protection of the masses of the composite quarks and leptons compared to their compositeness scale and (iv) inter–family mass–hierarchy. The existence of the two vector–like families – a prediction of the model – turns out to be crucial especially for an explanation of the inter–family mass–hierarchy (IFMH). Given the simplicity of the explanation, the observed IFMH in turn appears to us to be a strong hint in favor of the existence of the two vector–like families. This paper is devoted to a detailed study of the expected masses, mixings and decay modes of the fermions belonging to the two vector– like families, in the context of the SUSY preon model, with the inclusion of the renormalization–effects due to the standard model gauge interactions. Including QCD renormalization–effects, the masses of the vector–like quarks are expected to lie in the range of 500 GeV to about 2.5 TeV, while those of the vector–like leptons are expected to be in the range of 200 GeV to 1 TeV. Their mass pattern and decay modes exhibit certain distinguishing features and characteristic signals. For example, when the LHC and, possibly a future version of the SSC are built, pair–production of the vector–like quarks would lead to systems such as (bb+4Z +W+W−) and (bb+2Z +W+W−), while an e−e+ linear collider (NLC) of suitable energy can produce appreciably a single neutral heavy lepton N together with ντ , followed by the decay of N into (Z + ντ ) → (e−e+) + ντ . This last signal may conceivably materialize even at LEP 200 if N is lighter than about 190 GeV