Abstract
Recent improvements to OPUCEM, the tool for calculation of the contributions
of various models to oblique parameters, are presented. OPUCEM is used to
calculate the available parameter space for the four family Standard Model
given the current electroweak precision data. It is shown that even with the
restrictions on Higgs boson and new quark masses presented in the 2011 autumn
conferences, there is still enough space to allow a fourth generation with
Dirac type neutrinos. For Majorana type neutrinos, the allowed region is even
larger. The electroweak precision data also favors non-zero mixing between
light and fourth generations, thus effectively reducing current experimental
limits. Additionally, calculations with OPUCEM show that even 5th and 6th
generations are compatible with the existing electroweak precision data, with a
probability comparable to or higher than the Standard Model with 3 generations.
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