Charming New Physics in Beautiful Processes?

Abstract

In this thesis we study quark flavour physics and in particular observables relating to meson mixing and lifetimes. Meson mixing arises due to the nature of the weak interaction, and leads to several related observables that are highly suppressed in the Standard Model (SM). Alongside meson mixing, lifetimes provide an insight into rare processes which can shed light on possible new physics.

Both calculations are based on an Effective Field Theory (EFT) framework, in particular the Weak Effective Theory. This framework allows us to separate the high scale effects which are calculable in perturbation theory from the low energy matrix element which are determined through other means. Within this framework, the observables are expanded using the Heavy Quark Expansion (HQE) technique, which utilises the relatively large masses of and quarks to reveal a further hierarchy of corrections. The basics of EFTs and the HQE are explored in detail as an entry point to the majority of the work in this thesis.

In the rest of the thesis, we take aim at pushing the accuracy of our SM predictions further: by testing the underlying assumption of Quark-Hadron duality in the HQE; by studying possible new physics models that can explain the long standing problem of dark matter as well as recently seen anomalies; and by using alternative approaches to determining the low energy constants associated with mixing and lifetimes in order to provide independent and state-of-the-art results.