Quantum chromodynamics (QCD) is the theory of strong interactions between elementary particles and is, along with the electro-weak interactions, a component of the standard model of particle physics. Due to its nature, QCD interactions at low energies have to be studied non-perturbatively, which can be done by numerical simulations. From such simulations, properties like masses and decay rates of bound states of elementary particles, such as mesons or baryons, can be computed. These are directly accessible in experiments like the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN). The LATTICE FLAVOUR QCD (Flavour physics from lattice QCD at the physical point) project performed calculations for form factors and decay constants to extract certain elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix from experimental measurements. The CKM matrix elements are a further ingredient of the standard model, describing the mixing between the eigenstates of the electro-weak and strong theory. By testing for unitarity violations of the CKM matrix, one might be able to identify possible extensions of the standard model or rule them out. One approach was to calculate the kaon semi-leptonic form factor from lattice QCD simulations. Another approach examined the ratio of the kaon and pion decay constants, which allows extracting the ratio of CKM elements from the experimentally measured decay rates. A publication concerning results from the latter approach has been prepared. A second part of this research project determined low-energy constants of chiral perturbation theory (ChPT) from lattice simulations. ChPT is an effective field theory for low energies, resulting from an expansion in pion masses and momenta. Since in lattice simulations – in contrast to experiments – one can within a certain range freely vary the masses of the simulated quarks. Such simulations provide an ideal test bed for the predictions of ChPT. Results have been published in a paper in Physical Review D and in several conference proceedings.
Quantum chromodynamics, elementary particles, electro-weak, LATTICE FLAVOUR QCD, lattice simulations