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It is known that flavor democracy favors the existence of the fourth standard model (SM) family. In order to give nonzero masses for the first three-family fermions flavor democracy has to be slightly broken. A parametrization for democracy breaking, which gives the correct values for fundamental fermion masses and, at the same time, predicts quark and lepton Cabibbo-Kobayashi-Maskawa (CKM) matrices in a good agreement with the experimental data, is proposed. The pair productions of the fourth SM family Dirac $({\ensuremath{\nu}}_{4})$ and Majorana $({N}_{1})$ neutrinos at future linear colliders with $\sqrt{s}=500\text{ }\text{ }\mathrm{GeV}$, 1 TeV, and 3 TeV are considered. The cross section for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{4}{\overline{\ensuremath{\nu}}}_{4}({N}_{1}{N}_{1})$ and the branching ratios for possible decay modes of the both neutrinos are determined. The decays of the fourth family neutrinos into muon channels $({\ensuremath{\nu}}_{4}({N}_{1})\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{W}^{\ensuremath{\mp}})$ provide cleanest signature at ${e}^{+}{e}^{\ensuremath{-}}$ colliders. Meanwhile, in our parametrization this channel is dominant. $W$ bosons produced in decays of the fourth family neutrinos will be seen in detector as either di-jets or isolated leptons. As an example, we consider the production of 200 GeV mass fourth family neutrinos at $\sqrt{s}=500\text{ }\text{ }\mathrm{GeV}$ linear colliders by taking into account di-muon plus four jet events as signatures.
Published in: Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology
Volume 72, Issue 5