Lattice QCD with 2+1+1 dynamical quark flavors

Quantum chromodynamics (QCD) is the theory of quarks, gluons and their interactions. It explains, how and why quarks and gluons form bound states, so-called hadrons (e.g. protons or neutrons), which can be observed by means of particle accelerators, e.g. the LHC. The corresponding QCD equations are, however, rather complex and, therefore, can usually only be solved numerically by means of lattice QCD and by employing modern high performance computing systems. Numerically expensive is in particular the simulation of dynamical quarks, which appear in nature in six different flavors, which mainly differ in their masses. Until now only the two or three lightest quark flavors have been considered in simulations. To create an even more realistic setup, the aim of this project is to study various aspects of simulating and analyzing four dynamical quark flavors. In particular so-called mixed action setups will be implemented and studied, where in the sea sector rather cheap Wilson twisted mass quarks will be employed. In contrast to that valence quarks will be realized by Osterwalder-Seiler twisted mass quarks and by overlap quarks respectively, which exhibit certain additional symmetries playing an important role in QCD. Such setups will allow to study a variety of physical problems and questions. The main goals of this project are to study the spectrum of strange and charm mesons as fully as possible by means of the Osterwalder-Seiler setup as well as to perform a benchmark test of the overlap setup, the computation of the kaon bag parameter.