Topics in physics beyond the standard model

In this work, topics in physics beyond the standard model of high energy phyics relevant to the experimental studies at the Large Hadron Collider (LHC) at CERN are discussed. We introduce an effective theory to describe the dynamics of heavy Majorana particles, whose existence is predicted in many extensions of the standard model. Further, it is demonstrated how by combining the two independent concepts of a weakly interacting massive particle accounting for the dark matter observed in our universe and gauge coupling unification, strong phenomenological trends can be inferred. The scenario we present predicts new colored states within LHC reach that can be either collider stable or decay promptly to final states including a Higgs particle. In both cases, interesting LHC signatures are expected. The LHC discovery of the long predicted Higgs boson as well as new lower bounds on supersymmetric particle masses provide motivation to re-evaluate the issue of fine-tuning in supersymmetric theories. We provide an overview of the current state of this ongoing discussion. In the last part of this work we introduce an alternative approach termed stable near-criticality, in which the standard limits on superparticle masses stemming from fine-tuning considerations are relaxed. This approach requires specific and robust correlations among soft mass terms. We discuss how reduced fine-tuning can be achieved even if the gauge and Yukawa couplings are considered variable parameters. Finally, we illustrate our findings with a possible model implementation and demonstrate the validity of our approach by analysing a representative benchmark point.