Quasi Yukawa Unification and Fine-Tuning in U(1) Extended SSM
  We consider the low scale implications in the U(1)' extended MSSM (UMSSM). We restrict the parameter space such that the lightest supersymmetric particle (LSP) is always the lightest neutralino. In addition, we impose quasi Yukawa unification (QYU) at the grand unification scale (M_GUT). QYU strictly requires the ratios among the yukawa couplings as y_t/y_b ~ 1.2, y_tau/y_b ~ 1.4, and y_t/y_tau ~ 0.8. We find that the need of fine-tuning over the fundamental parameter space of QYU is in the acceptable range (Delta_EW <= 10^3), even if the universal boundary conditions are imposed at M_ GUT, in contrast to CMSSM and NUHM. UMSSM with the universal boundary conditions yields heavy stops (m_{stop} >~ 2.5 TeV), gluinos (m_gluino >~ 2 TeV), and squarks from the first two families (m_squarks >~ 4 TeV). Similarly the stau mass is bounded from below at about 1.5 TeV. Despite this heavy spectrum, we find Delta_EW >~ 300, which is much lower than that needed for the minimal supersymmetric models. In addition, UMSSM yield relatively small mu-term, and the LSP neutralio is mostly form by the Higgsinos of mass >~ 700 GeV. We obtain also bino-like dark matter (DM) of mass about 400 GeV. Wino is usually found to be heavier than Higgsinos and binos, but there is a small region where mu ~ M_1 ~ M_2 ~ 1 TeV. We also identify chargino-neutralino coannihilation channel and A-resonance solutions which reduce the relic abundance of LSP neutralino down to the ranges compatible with the current WMAP measurements. 
Yasar Hicyilmaz, Meltem Ceylan, Asli Altas, Levent Solmaz and Cem   Salih Un
hep-ph