  We introduce the "Dirac similarity principle" that states that only those
point-like Dirac particles which can interact with the Dirac electron can be
observed, such as in the Standard Model. We emphasize that the existing world
of the Standard Model is a Dirac world satisfying the Dirac similarity
principle and believe that the immediate extension of the Standard Model will
remain to be so. On the other hand, we are looking for Higgs particles for the
last forty years but something is yet to be found. This leads naturally to the
"minimum Higgs hypotheses".
  Now we know firmly that neutrinos have tiny masses, but in the minimal
Standard Model there is no natural sources for such tiny masses. If nothing
else, this could be taken as the clue as the signature of the existence of the
extra heavy $Z^{\prime 0}$ since it requires the extra Higgs field, that would
help in generating the neutrino tiny masses. Alternatively, we may have missed
the right-hand sector for some reason. A simplified version of the left-right
symmetric electroweak model has the simplest Higgs sector (in which there is
one standard left-hand Higgs doublet together with the image right-handed Higgs
doublet), of which the Higgs sector also satisfies the "minimum Higgs
hypothesis". Or, if we question the origin of the family symmetry, we may
consider to enlarge it to the family gauge symmetry. It transpires very feeble
family interactions. All the above possibilities satisfy both the so-called
"Dirac similarity principle", the "minimum Higgs hypothesis", and
renormalizability.
