Computational quantum field theory and global fits of effective dark matter models

Abstract

The search for physics beyond the Standard Model is necessarily a multi-disciplinary field. By including all data relevant to a particle physics model simultaneously in a ‘global fit’, it is possible to make statistically meaningful statements about the viability of theories beyond the Standard Model. The topics of this thesis are extending the global fitting software framework GAMBIT, and performing global fits of effective dark matter models. Firstly, I present GUM, the GAMBIT Universal Model Machine, a tool that interfaces sym- bolic Lagrangian-level tools and GAMBIT to allow one to implement new physics models in GAMBIT with minimal effort. I perform a fit of a simplified dark matter model using GUM and GAMBIT. Next, I present CosmoBit, the new GAMBIT module for cosmological observables and likeli- hoods. I present an application of CosmoBit in which I perform a global analysis to place limits on the lightest neutrino mass by consistently combining cosmological and terrestrial datasets. I then consider global fits of effective dark matter models using GAMBIT. I consider models in which the Standard Model is extended by either a fermionic or vector dark matter candidate that interacts via the ‘Higgs portal’. I present comprehensive results in both frequentist and Bayesian frameworks, combining constraints from direct detection, indirect detection from γ rays and neutrinos, the invisible width of the Higgs, and the relic abundance of dark matter, whilst ensuring that the effective model description does not break down. Finally, I perform global fits of dark matter effective field theories defined at the partonic level, in which a dark matter candidate interacts with quarks and gluons via effective contact interactions. I consider cases in which the effective theory is generated by integrating out either a scalar mediator, a vector mediator, or a heavy quark. In these fits, I combine constraints from direct detection, indirect detection from γ rays, monojet searches for dark matter particles from the LHC, and the relic abundance of dark matter.