Fine tuning in small and large tan beta regions in the cE6SSM

The Electroweak sector in E6 supersymmetric models is subject to a degree of fine tuning in the percent to permil level. This can be attributed to the experimental limits on both the mass of the Z' boson associated with the extra U(1)' symmetry in the model, as well as the masses of naturalness-related sparticles (which is a general source of tuning in supersymmetric models). The degree of tuning can be smaller than that in the minimal supersymmetric standard model with universal fundamental parameters (the constrained MSSM). We show this by quantifying the fine tuning in regions of the parameter space of the constrained exceptional supersymmetric standard model (cE6SSM) corresponding to values of tan beta below and above 10. It is found that, a Higgs mass m_h ~ 125 GeV, a gluino mass ~ 1.5 TeV, and a Z' boson mass m_Z' ~ 3.8 TeV correspond to fine tuning in the 0.2% (0.1%) level for tan beta = 30 (5).

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