Light stops and fine-tuning in MSSM

• Main Authors: Ali Çiçi, Zerrin Kırca, Cem Salih Ün
• Format: Article
• Language: English
• Published: SpringerOpen 2018-01-01
• Series: European Physical Journal C: Particles and Fields
• Online Access: http://link.springer.com/article/10.1140/epjc/s10052-018-5549-y

Abstract We discuss the fine-tuning issue within the MSSM framework. Following the idea that the fine-tuning can measure effects of some missing mechanism, we impose non-universal gaugino masses at the GUT scale, and explore the low scale implications. We realize that the fine-tuning parametrized with $$\Delta _{EW}$$ ΔEW can be as low as zero. We consider the stop mass with a special importance and focus on the mass scales as $$m_{\tilde{t}} \le 700$$ mt~≤700 GeV, which are excluded by the current experiments when the stop decays into a neutralino along with a top quark or a chargino along with a bottom quark. We find that the stop mass can be as low as about 250 GeV with $$\Delta _{EW} \sim 50$$ ΔEW∼50 . We find that the solutions in this region can be exluded only up to $$60\%$$ 60% when stop decays into a neutralino-top quark, and $$50\%$$ 50% when it decays into a chargino-b quark. Setting $$65\%$$ 65% CL to be potential exclusion and $$95\%$$ 95% to be pure exclusion limit such solutions will be tested in near future experiments, which are conducted with higher luminosity. In addition to stop, the region with low fine-tuning and light stops predicts masses for the other supersymmetric particles such as $$m_{\tilde{b}} \gtrsim 700$$ mb~≳700 GeV, $$m_{\tilde{\tau }} \gtrsim 1$$ mτ~≳1 TeV, $$m_{\tilde{\chi }_{1}^{\pm }} \gtrsim 120$$ mχ~1±≳120 GeV. The details for the mass scales and decay rates are also provided by tables of benchmark points.