Supersymmetry at the crossroads: Higgs, dark matter and collider signals

Ajaib, Muhammad Adeel
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University of Delaware
Supersymmetry (SUSY) is one of the most elegant extensions of the standard model (SM) of particle physics. It solves several problems in the SM, supports the idea of grand unification and also provides a candidate for dark matter. The recent discovery of the Higgs boson is consistent with the lightest Higgs boson in Minimal Supersymmetric Standard Model. However, to date, no signals of supersymmetry were found at the LHC. The presence of the Higgs boson and the absence of supersymmetric particles at the LHC can significantly impact various SUSY models. The topic of this dissertation is to demonstrate how supersymmetry is being tested at various fronts in the era of the Large Hadron Collider (LHC). We will employ SUSY searches from the LHC to derive a model dependent limit on the supersymmetric top quark mass when it is next to the lightest to the SUSY dark matter candidate. We will also address the impact of these observations on the SUSY dark matter candidate. Furthermore, if SUSY is present at LHC accessible energies it can effect the rate at which the Higgs boson decays to some final states. We will discuss how the decay rate of the Higgs boson to two photons can be affected in the presence of SUSY and show that the supersymmetric partner of the tau particle, the stau, can account for an enhancement in this channel. One of the popular mechanisms of SUSY breaking is the minimal gauge mediated SUSY breaking model. We will show that a 125 GeV Higgs severely constrains the minimal version of this model. It implies that, with the exception of the stau, all the SUSY particles are heavy enough to evade detection at the LHC. Finally, we demonstrate that a 125 GeV Higgs boson can also hint to a particular grand unified model. We shall discuss the SO(10) grand unified model with t -b -τ Yukawa unification and show that the Higgs boson mass can be predicted in this model.