Quasi-Yukawa unification and fine-tuning in U(1) extended SSM

Abstract

We consider the low scale implications in the U(1)' extended minimal supersymmetric Standard Model (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) similar to 1.2, y(tau)/y(b) similar to 1.4, and y(t)/y(tau) similar to 0.8. We find that the need for 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 nonuniversal Higgs masses. The UMSSM with universal boundary conditions yields heavy stops (m((t) over tilde) greater than or similar to 2.5 TeV), gluinos (m((g) over tilde) greater than or similar to 2 TeV), and squarks from the first two families (m((q) over tilde) greater than or similar to 4 TeV). Similarly, the stau mass is bounded from below at about 1.5 TeV. Despite this heavy spectrum, we find Delta(EW) greater than or similar to 300, which is much lower than that needed for the minimal supersymmetric models. In addition, the UMSSM yields a relatively small mu term, and the LSP neutralino is mostly formed by the Higgsinos of mass. greater than or similar to 700 GeV. We also obtain bino-like dark matter of mass about 400 GeV. The wino is usually found to be heavier than Higgsinos and binos, but there is a small region where mu similar to M-1 similar to M-2 similar to 1 TeV. We also identify a chargino-neutralino coannihilation channel and A-resonance solutions which reduce the relic abundance of LSP neutralinos down to the ranges compatible with the current WMAP and Planck measurements.