Signs of Susy

Abstract

After a brief introduction to 21st century fundamental physics suitable for the layman with a reasonable level of mathematical competence, I introduce the concept of unnaturalness in Standard Model electroweak symmetry breaking and Supersymmetry (Susy) as a potential solution. The optimally natural situation in Susy in light of the 2012 discovery of a Higgs boson is derived, namely that of almost maximal mixing, with the scalar top partners almost as light as can be. The discovery is also interpreted numerically in terms of the Next-to-Minimal Supersymmetric Standard Model, with greater emphasis placed on the visibility of the Higgs boson at the observed mass, i.e. on signal strengths. I introduce simple models of gauge-mediated Susy breaking (GMSB), and how their generalisation leads to a richer parameter space. I then investigate the role played by the mediation scale of GMSB: this is found to be as a control of the extent to which Yukawa couplings de-tune flavour-blind relations set by gauge couplings. Finally, issues relating to the discovery or exclusion of Susy at colliders are discussed. Bounds are derived for the masses of new particles from Large Hadron Collider searches for excesses of jets and missing energy without leptons, and compared to constraints arising from Higgs boson searches, for models of GMSB and the Constrained Minimal Supersymmetric Standard Model. I present a novel search strategy for new physics signatures with two neutral, stable particles, when such particles are produced by boosted decays. (Susy examples include models with light gravitinos, pseudo-goldstinos, singlinos or new photinos.) The method is shown to produce sharp mass peaks that enhance the visibility of the signal.