The Naturalness of the Fourth SM Family

The necessity of the fourth family follows from the SM basics. According to flavor democracy the Dirac masses of the fourth SM family fermions are almost equal with preferable value 450 GeV, which corresponds to common (for all fundamental fermions) Yukawa coupling equal to SU(2) gauge coupling gW. In principle, one expect u4 a little bit lighter than d4, while nu4 could be essentially lighter than l4 due to Majorana mass terms for right-handed components of neutrinos. Obviously, the fourth family quarks will be copiously produced at the LHC. However, the first indication of the fourth SM family may be provided by early Higgs boson observation due to almost an order enhancement of the gluon fusion to Higgs cross-section. For the same reason the Tevatron still has a chance to observe the Higgs boson before the LHC. Concerning the fourth family leptons, in general, best place will be NLC/CLIC. However, for some mass regions and MNS matrix elements double discovery of both the nu4 and H could be possible at the LHC.