On the Suppression of the Dark Matter-Nucleon Scattering Cross Section in the SE6SSM

In the E6 inspired U(1)N extension of the minimal supersymmetric (SUSY) standard model (MSSM), a single discrete Z˜2H symmetry permits suppressing rapid proton decay and non-diagonal flavor transitions. If matter parity and Z˜2H symmetry are preserved in this SUSY model (SE6SSM), it may involve two dark matter candidates. In this article, we study a new modification of the SE6SSM in which the cold dark matter is composed of gravitino and the lightest neutral exotic fermion. We argue that, in this case, the dark matter nucleon scattering cross-section can be considerably smaller than the present experimental limit.

E6 GUT and Baryon Asymmetry Generation in the E6CHM

Grand unified theories (GUTs) may result in the E6-inspired composite Higgs model (E6CHM) at low energies, almost stabilizing the electroweak scale. We consider an orbifold GUT in 6 dimensions in which the E6-gauge group is broken to the gauge symmetry of the standard model (SM) while different multiplets of the SM fermions come from different 27-plets. The strongly coupled sector of the E6CHM is confined on the brane where E6 is broken down to its SU(6) subgroup. Near the scale of f≳5TeV, this approximate SU(6) symmetry is expected to be further broken down to its SU(5) subgroup, which contains the SM-gauge group. Such a breakdown leads to a set of pseudo-Nambu–Goldstone bosons (pNGBs) that includes an SM-like Higgs doublet. The approximate gauge coupling unification in the E6CHM takes place at high energies when the right-handed top quark is a composite fermion. To ensure anomaly cancellation, the weakly coupled sector of this model contains extra exotic matter beyond the SM. We discuss the mechanism of the generation of matter–antimatter asymmetry within the variant of the E6CHM in which the baryon number and CP invariance are violated.

A Review of the Exceptional Supersymmetric Standard Model

Local supersymmetry (SUSY) provides an attractive framework for the incorporation of gravity and unification of gauge interactions within Grand Unified Theories (GUTs). Its breakdown can lead to a variety of models with softly broken SUSY at low energies. In this review article, we focus on the SUSY extension of the Standard Model (SM) with an extra U ( 1 ) N gauge symmetry originating from a string-inspired E 6 GUTs. Only in this U ( 1 ) extension of the minimal supersymmetric standard model (MSSM) can the right-handed neutrinos be superheavy, providing a mechanism for the baryon asymmetry generation. The particle content of this exceptional supersymmetric standard model (E 6 SSM) includes three 27 representations of the E 6 group, to ensure anomaly cancellation. In addition it also contains a pair of S U ( 2 ) W doublets as required for the unification of gauge couplings. Thus, E 6 SSM involves exotic matter beyond the MSSM. We consider symmetries that permit suppressing flavor changing processes and rapid proton decay, as well as gauge coupling unification, the gauge symmetry breaking and the spectrum of Higgs bosons in this model. The possible Large Hadron Collider (LHC) signatures caused by the presence of exotic states are also discussed.