Akademik Veri Yönetim Sistemi
European Physical Journal C, cilt.72, sa.4, ss.1-11, 2012 (SCI-Expanded)
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 parameter space is even larger. The electroweak precision data also appear to favor non-zero mixing between light and fourth generations, thus effectively reducing the current experimental limits on the masses of the new quarks, which assume that the mixing with the third generation is dominant. Additionally, disregarding the lack of a clear Higgs signal from the LHC and focusing only an electroweak precision data comptability, calculations with OPUCEM show that, the existing electroweak data are compatible with the presence of a 5th and also a 6th generation in certain regions of the parameter space. © 2012 The Author(s).