We make a comprehensive study of the theory and phenomenology of a low energy supersymmetric standard model originating from a string-inspired E 6 grand unified gauge group. The Exceptional Supersymmetric Standard Model (ESSM) considered here is based on the low energy SM gauge group together with an extra Z ′ corresponding to an extra U (1) N gauge symmetry under which right-handed neutrinos have zero charge. The low energy matter content of the ESSM corresponds to three 27 representations of the E 6 symmetry group, to ensure anomaly cancellation, plus an additional pair of Higgs-like doublets as required for high energy gauge coupling unification. The ESSM is therefore a low energy alternative to the MSSM or NMSSM. The ESSM involves extra matter beyond the MSSM contained in three 5 + 5 * representations of SU (5), plus three SU (5) singlets which carry U (1) N charges, one of which develops a VEV, providing the effective µ term for the Higgs doublets, as well as the necessary exotic fermion masses. We explore the RG flow of the ESSM and examine theoretical restrictions on the values of new Yukawa couplings caused by the validity of perturbation theory up to the Grand Unificationscale. We then discuss electroweak symmetry breaking and Higgs phenomenology, and establish an upper limit on the mass of the lightest Higgs particle which can be significantly heavier than in the MSSM and NMSSM, in leading two-loop approximation. We also discuss the phenomenology of the Z ′ and the extra matter, whose discovery will provide a smoking gun signal of the model.

The Higgs boson spectrum of the Next-to-Minimal Supersymmetric Standard Model is ex-

We discuss some phenomenological aspects of an E 6 inspired supersymmetric standard model with an extra U (1) N gauge symmetry under which right-handed neutrinos have zero charge, allowing a conventional see-saw mechanism. The µ problem is solved in a similar way to the NMSSM, but without the accompanying problems of singlet tadpoles or domain walls. The above exceptional supersymmetric standard model (ESSM) involves the low energy matter content of three 27 representations of E 6 , which is broken at the GUT scale, and allows gauge coupling unification due to an additional pair of Higgs-like doublets. The ESSM predicts a Z ′ boson and exotic quarks which, if light enough, will provide spectacular new physics signals at the LHC. We study the LHC phenomenology of the Z ′ and extra quarks, including their production and decay signatures particular to the ESSM. We also discuss the two-loop upper bound on the mass of the lightest CP-even Higgs boson, and show that it can be significantly heavier than in either the MSSM or the NMSSM.

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non-perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches. *

We propose and study a constrained version of the exceptional supersymmetric standard model (E 6 SSM), which we call the cE 6 SSM, based on a universal high energy scalar mass m 0 , trilinear scalar coupling A 0 and gaugino mass M 1=2 . We derive the renormalization group (RG) Equations for the cE 6 SSM, including the extra Uð1Þ N gauge factor and the low-energy matter content involving three 27 representations of E 6 . We perform a numerical RG analysis for the cE 6 SSM, imposing the usual lowenergy experimental constraints and successful electroweak symmetry breaking. Our analysis reveals that the sparticle spectrum of the cE 6 SSM involves a light gluino, two light neutralinos, and a light chargino. Furthermore, although the squarks, sleptons, and Z 0 boson are typically heavy, the exotic quarks and squarks can also be relatively light. We finally specify a set of benchmark points, which correspond to particle spectra, production modes, and decay patterns peculiar to the cE 6 SSM, altogether leading to spectacular new physics signals at the Large Hadron Collider.