Abstract

In this PhD thesis we investigate various aspects of phenomenology of new physics beyond the Standard Model (SM) in the context of extensions of supersymmetric \& non-supersymmetric realisations.

In extensions of supersymmetric realisations, we first study the low scale predictions of the supersymmetric standard model extended by $U(1)_{B-L}\times U(1)_{R}$ symmetry, obtained from $SO(10)$ breaking via a left-right supersymmetric model, imposing universal boundary conditions. We find that the lightest neutralino or sneutrino emerge as dark matter candidates, with different low scale implications. Secondly, we perform a comprehensive analysis of the secluded UMSSM model, consistent with present experimental constraints. In this model the additional $Z^\prime$ gauge boson can be leptophobic without resorting to gauge kinetic mixing and, thus lowering the LHC bounds on its mass. Thirdly, we test $E_6$ realisations of a generic $U(1)'$ extended Minimal Supersymmetric Standard Model (UMSSM) against all currently available data, from space to ground experiments, from low to high energies. Large gauge kinetic mixing implies that the $Z'$ boson emerging from the breaking of the additional $U(1)'$ symmetry is rather wide since it decays mainly into $WW$ pairs.

In extensions of non-supersymmetric realisations, we study mass bounds of the $W_R$ gauge boson in generic left-right symmetric models. Assuming that the gauge bosons couple universally to quarks and leptons, we allow different gauge couplings $g_R \ne g_L$ and mass mixing, $V_{CKM}^L \ne V_{CKM}^R$ in the left and right sectors. $W_R$ mass bounds can be considerably relaxed, while $Z_R$ mass bounds are much more stringent. In addition, we perform a consistent analysis of the alternative left-right symmetric model emerging from $E_6$ grand unification. We show that the exotic neutrino inherent to this class of models, the scotino, is a viable candidate for dark matter satisfying relic density and direct detection constraints.