Goethe-Universität Frankfurt am Main - Institut für Theoretische Physik

Heisenberg Professorship "Exotic mesons from lattice QCD"


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Research interests of our group

We are working in the field of theoretical particle physics and quantum field theory with particular focus on lattice gauge theory. Lattice gauge theory is a non-perturbative numerical technique to compute path integrals in gauge theories, in particular in QCD. It is, therefore, suited to determine QCD observables like hadron masses and decay constants from first principles, the QCD Lagrangian. All possible sources of systematic error (discretization errors, finite volume corrections, unphysically heavy up/down quark masses) can systematically be investigated and removed by means of controlled extrapolations.

In recent years it has become possible to simulate QCD with physically realistic setups including 2, 2+1 or 2+1+1 dynamical quark flavors, light up/down quark masses, which are close to or even at their physical value, large spacetime volumes to exclude finite volume effects and small values of the lattice spacing, to reliably perform continuum extrapolations. Numerical results obtained with such setups allow direct comparisons to experimental results and, consequently, to verify QCD up to experimental or numerical precision or, equivalently, to search for new physics. Alternatively, one can perform simulations in physical situations or for specific physical processes, where experiments are difficult to perform or currently even impossible, e.g. at very high temperatures. Finally, such simulations can help to get a better understanding of QCD, e.g. by investigating the structure of mesons or baryons or by computing interactions between quarks or between mesons and/or baryons.

In detail we are interested in the following topics.

Exotic mesons from lattice QCD

Quantum chromodynamics (QCD) is an important part of the Standard Model of particle physics. It is a quantum field theory describing quarks and gluons and their interactions. At low temperature and density one does not observe isolated quarks. Quarks always appear in groups, which are bound together by gluons and are denoted as hadrons. Typically one finds either quark-antiquark pairs qq, so-called mesons, or triplets of quarks qqq or antiquarks qqq, so-called baryons or anti-baryons. While the most prominent hadrons are the proton and the neutron, several hundred different types of mesons and baryons have been observed experimentally. They differ in their flavor content and in other quantum numbers, e.g. total angular momentum or parity.

In our research we mainly focus on mesons. Comparatively simple quark model calculations assuming a quark-antiquark structure reproduce experimentally measured properties like masses or decay rates for most mesons rather precisely. Thus, they have led to a solid understanding of many qq or non-exotic mesons. There are, however, several mesonic systems, which cannot be explained within such a quark-antiquark picture, and which seem to have a more complicated structure or quantum numbers excluded in qq quark model calculations.

For exotic mesons several structures different from qq are discussed, but none of them is either experimentally or theoretically confirmed or ruled out (see also the figure below). The major goal of our research is to study mesons from first principles using lattice QCD and to confirm or rule out the existence of exotic structures like tetraquarks or hybrid mesons in certain channels. Moreover, the goal is to understand their internal structure (e.g. "Is a specific tetraquark a mesonic molecule or rather a diquark-antidiquark pair?", "What is the preferred shape of the flux tube of a specific hybrid meson?") and the corresponding binding mechanism (e.g. "Which quantum numbers and which quark flavor combinations favor the existence of exotic mesons?").

exotic_mesons.jpg

Inhomogeneous phases in QCD-inspired models

Our research on inhomogeneous phases in QCD-inspired models is part of the DFG funded Collaborative Research Center TransRegio 211 "Strong-interaction matter under extreme conditions", in particular of "Project A03 - Inhomogeneous phases at high density". Detailed information can be found on the following webpages:


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