Subproject A4: Chirally invariant and twisted mass formulations of QCD on the lattice

Project Leader:
Prof. Michael Müller-Preußker, Department of Physics, Humboldt-University Berlin
Dr.rer.nat.habil. Karl Jansen, John-von-Neumann-Institute of Computing, DESY Zeuthen)


In this project two kind of lattice fermions, maximally twisted mass quarks and chiral invariant overlap fermions will be considered.

When including in the maximally twisted mass formulation of lattice QCD a mass-degenerate up and down quark-doublet (Nf=2), the lattice theory has been proved to lead to a very good O(a2) lattice spacing scaling such that precise values of many physical observables can be obtained in the continuum limit. We want to continue this research direction by including now also the strange and the charm quark as dynamical degrees of freedom in the twisted mass setup (Nf=2+1+1). This is a novel approach that will allow for the first time to realistically explore the heavy quark sector and in particular the charm sector.

We plan to essentially repeat the very successful research programme of the Nf=2 studies with Nf=2+1+1 flavours. A special emphasis will be the approach to the physical point where the pion mass assumes its experimentally measured value. To this end, a detailed and precise map of the quark mass dependence of many physical observables will be performed. We emphasize that in this project the methodological and conceptual questions will be in the focus of our research. This concerns in particular the study of cut-off and finite volume effects as well as the description of the quark mass behaviour of physical quantities towards the physical point.

As another research direction, we aim at investigations of the theory at non-vanishing temperature. We will make use of the improved continuum limit behaviour of maximally twisted mass fermions in order to reach physical results in a controlled way. Employing the knowledge of the phase diagram obtained by us, we are going to determine the critical behaviour and to explore the equation of state.

Finally, for quantities where chiral symmetry is expected to play an important role, such as BK,K → π π,ε'/ε, or questions related to topology, we want to use chirally invariant overlap fermions as valence quarks on a twisted mass sea.

The larger subproject (for T=0) is embedded into the large European Twisted Mass Collaboration (ETMC) with partners from 16 institutes from 9 different European countries, whereas the subproject atT>0 is related to a collaboration of HU Berlin with University of Bonn (C. Urbach), University of Frankfurt and INFN Frascati (tmfT Collaboration).

Last Change: 15th June 2011