Monte Carlo simulations of physics beyond the standard model

Abstract

The Large Hadron Collider, currently under construction at CERN, will give direct access to physics at the TeV scale for the first time. The lack of certainty over the type of physics that will be revealed has produced a wealth of ideas for so-called Beyond the Standard Model physics, all with the aim of solving the problems possessed by the Standard Model. The oldest and most well studied is supersymmetry but new ideas based on extra dimensions and collective symmetry breaking have been proposed more recently. In order to study these models most effectively, we argue that they must be implemented within the framework of a Monte Carlo event generator so that their signals can be studied in a real world setting. In this thesis we develop a general approach for the simulation of new physics models with the aim of reducing the effort in implementing a new model into the Herwig++ event generator. The approach is based upon the external spin structures of production and decay matrix elements so that the amount of information required to input a new model is simply a set of Feynman rules and mass spectrum. The first method uses an on-shell approximation throughout but this is later refined to include the effects of finite widths, as these are found to be important when processes occur close to threshold. In all of the discussions regarding our new approach we make specific reference to two models of new physics, the Minimal Supersymmetrie Standard Model and the Minimal Universal Extra Dimensions model. Our general matrix elements and approach to finite widths are all demonstrated and tested using examples from these two models. The concluding discussion makes use of a third model, the Littlest Higgs model with T-parity, such that signals from the three models are compared and contrasted using the general framework developed here.