Professor Anthony Williams
University of Adelaide
The Standard Model (SM) of particle physics has successfully predicted the bottom quark, the top quark, the W and Z massive vector bosons, the tau neutrino and the Higgs boson. The apparent recent discovery of the Higgs boson at the Large Hadron Collider (LHC) was particularly noteworthy as the confirmation of spontaneous electroweak symmetry breaking and the origin of the masses of fundamental particles. Furthermore, the SM has withstood the precision electroweak tests performed at the Large Electron-Positron (LEP) collider and elsewhere. Despite the very impressive successes of the SM in precisely describing physics over approximately 40 orders of magnitude in terms of 19 parameters, there are clear gaps and the SM is not a complete description of the currently known universe. It does not unify gravity with the other three forces and does not explain Dark Energy and the apparent accelerating expansion of the universe. It does not include a description of Dark Matter and it does not provide a unification of the other three SM forces into a single Grand Unified Theory (GUT). In addition, the very success of the Higgs mechanism provides an additional challenge in the form of the hierarchy problem, where physics beyond the SM is needed to understand how the mass of the Higgs boson could naturally be as small as 125-126 GeV. Supersymmetry (SUSY) and composite Higgs models are possible explanations of the hierarchy problem, but the current absence of any Beyond the Standard Model (BSM) physics signatures at the LHC is already causing tension with these potential BSM explanations. This talk will describe and explore these issues.