Searching New Physics using Flavour

ended

After ten years from the discovery of the Higgs boson at CERN, which established the Standard Model (SM) of particle physics as the most accurate description of nature at its fundamental level, no direct sign of new physics (NP) beyond the SM has been observed. In order to make further progress in high-energy physics, it is necessary to improve the precision of theoretical SM predictions and search NP effects indirectly by looking for tiny discrepancies with experimental measurements. This proposal will make use of a combination of formal and numerical tools, in particular methods of numerical lattice quantum chromodynamics (QCD), to achieve this aim in the context of flavour physics. Two projects are proposed, which have the common goal of improving the precision on theoretical predictions of relevant flavour observables and share the difficulty of being dominated by hadronic effects that require non-perturbative lattice calculations. In the first project, I will study the leading electromagnetic and strong isospin breaking corrections to kaon semi-leptonic decays, providing a method to extract the relevant decay amplitudes from finite-volume (FV) Euclidean correlation functions evaluated on the lattice and computing analytically their FV dependence. This aims to determine the CKM matrix element Vus with sub-percent precision and hence to test the CKM matrix unitarity predicted by the SM. The goal of the second project is instead to obtain a first non-perturbative estimate of long-distance contributions to the mixing of neutral D mesons, which are dominant but poorly known, thus representing a limiting factor in the study of CP violation and NP effects in this process. This will be done by applying advanced reconstruction techniques to FV lattice spectral functions. This proposal will have a relevant impact on flavour physics and phenomenology, delivering new conceptual and algorithmic methods which will provide the foundations for future scientific progress.