Light stops and fine-tuning in MSSM


Cici A., KIRCA Z., ÜN C. S.

EUROPEAN PHYSICAL JOURNAL C, vol.78, no.1, 2018 (SCI-Expanded) identifier identifier

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) can be as low as zero. We consider the stop mass with a special importance and focus on the mass scales as m((t) over tilde) <= 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) similar to 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 m((b) over tilde) greater than or similar to 700 GeV, m((tau) over tilde) greater than or similar to 1 TeV, m((chi) over tilde1) +/- greater than or similar to 120 GeV. The details for the mass scales and decay rates are also provided by tables of benchmark points.