Effective field theories for general extensions of the Standard Model with new particles

Abstract

The current situation in particle physics involves a large number of both theoretical proposals and experimental measurements. The relation between the two is often intricate, as every new physics model comes with its own set of motivations and predictions, and each measurement that is performed has consequences for many theoretical models. The purpose of this thesis is to set the basis for a general, organized and efficient way of dealing with these issues. At first sight, a naive systematic approach to the problem may be devised: pick a representative set of models together with a sufficiently extensive set of observables, and compute every observable for each model. This procedure suffers from several drawbacks. Firstly, it is not easy to decide which models and observables to include: if there are too many, the task becomes impossible in practice, but one risks not being general enough otherwise. Secondly, it is inefficient: similar calculations will be performed many times. Lastly, it does not scale well: if a new kind of model becomes interesting, one has to recompute the value of all observables; and if a new experiment is designed, then one has to go back to every model to compute the observables that are going to be measured. Roughly speaking, the number of calculations that need to be performed grows as the product of the number of models and the number of observables of interest.