Light stops and fine-tuning in MSSM

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 Δ EW can be as low as zero. We consider the stop mass with a special importance and focus on the mass scales as 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 Δ EW∼ 50. We find that the solutions in this region can be exluded only up to 60 % when stop decays into a neutralino-top quark, and 50 % when it decays into a chargino-b quark. Setting 65 % CL to be potential exclusion and 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 mb~≳ 700 GeV, mτ~≳ 1 TeV, mχ~1±≳120 GeV. The details for the mass scales and decay rates are also provided by tables of benchmark points.