Flavour Expedition to the Zeptouniverse

Abstract

After the completion of the Standard Model (SM) through the Higgs discovery in 2012 particle physicists are waiting for the discovery of new particles either directly with the help of the Large Hadron Collider (LHC) or indirectly through quantum fluctuations causing certain rare processes to occur at different rates than predicted by the SM. While the later route is very challenging, requiring very precise theory and experiment, it allows in principle a much higher resolution of short distance scales than it is possible with the help of the LHC. In fact, in the coming flavour precision era, in which the accuracy of the measurements of rare processes and of the relevant lattice QCD calculations will be significantly increased, there is a good chance that we may get an insight into the scales as short as 10−21 m (Zeptouniverse) corresponding to energy scale of 200TeV or even shorter distance scales. We discuss the requirements that have to be met for such a flavour expedition to the Zeptouniverse to be successful. In particular we emphasize the power of correlations between flavour observables in the search for New Physics (NP) and identify a number of correlations that could allow to discover NP even if it would appear at the level of 20% of the SM contributions. The correlation between B(K+→ π+νν), B(Bs → μ+μ−) and γ extracted from tree-level decays within the SM is one of them. After presenting the simplest correlations in CMFV and U(2)3 models we address the recent data on Bs,d → μ+μ− and the anomalies in Bd → K(K∗)μ+μ−, including breakdown of lepton flavour universality, in the context of Z′-models with quark flavour violating neutral couplings. A brief discussion of leptoquark models is also given. We emphasize the correlations of Bd → K(K∗)μ+μ− with Bd → K(K∗)νν that allow to distinguish between various explanations of the anomalies in question. Finally, we summarize the recent study of K→ πνν and Bd,s→ μ+μ− decays which demonstrates that these decays play important roles in finding out what happens in the Zeptouniverse.