125 Higgs and Little Hierarchy in Extended Minimal Supersymmetric Standard Model

Abstract

In this thesis we have discussed the impact of 125 GeV Higgs mass on little hierarchy in Minimal Supersymmetric Standard Model (MSSM). We used the framework of constrained minimal supersymmetric standard model (cMSSM), in which the fermion masses, the boson masses and trilinear cou- plings are universal at GUT scale. In order to get 125 GeV CP-even neutral Higgs mass in MSSM, large radiative corrections are required. This requires large stop mass and trilinear couplings and therefore some fine tuning is required between MSSM parameters to get correct Z-boson mass. This fine tuning introduces hierarchy between Z-boson mass and stop mass and it is known as little hierarchy problem. Actually the degree of fine tuning in MSSM with 125 GeV Higgs is 0.27% while the acceptable range is &10%. To tackle this problem, we extend the matter contents of MSSM with new vectorlike particles which belong to 10+10 representation of SU(5). To avoid mixing of this new matter with quarks, these superfields have been assigned the same R-parity as MSSM Higgs chiral superfields. The Yukawa coupling of new particles with Higgs is considered to be small, otherwise new matter will exacerbate the little hierarchy problem. In this extended MSSM, the degree of fine tuning is improved from 0.27% to 5.85%.