The Naturalness of the Fourth SM Family

Understand

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.