"A Hint From the Inter-Family Mass Hierarchy: Two Vector-Like Families in the TeV range"

Abstract

Two vector-like families 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 in the context of a viable and economical SUSY composite model. One of the many attractive features of the model is an explanation of the inter-family mass-hierarchy for which the existence of the two vector-families is crucial. 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. 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 ($b\overline{b}+4Z+W^+W^-$) and ($b\overline{b}+2Z+W^+W^-$), while an $e^-e^+$ linear collider (NLC) of suitable energy can produce appreciably a single neutral heavy lepton $N$ together with $ν_τ$, followed by the decay of $N$ into $(Z+ν_τ) \rightarrow (e^-e^+) + ν_τ$. This last signal may conceivably materialize even at LEP 200 if $N$ is lighter than about 190 GeV.