Coordination Funds

• Applicant: Professor Dr. Francesco Knechtli
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Mathematics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 451886959

Quantum Chromodynamics (QCD) is the sector of the standard model describing the strong nuclear force, which binds quarks and gluons inside hadrons. The theory confines the constituents of hadrons, which are never observed directly in experiment. As a result, connecting experimental phenomena to the strongly coupled quantum field theory remains extremely challenging. In particular, the nature of confinement and physical signatures of confined gluons remain very poorly understood. The study of charmonium, a system containing a charm quark-anti-quark pair underwent a revolution after a number of entirely unexpected narrow resonances called the X, Y and Zs were discovered by experiments at the start of the new millennium. The nature of these resonances is still unclear. Similarly, interest in glueballs, hadrons made predominantly of confined gluons, has revived recently. A number of challenging physics questions for theory are raised by recent and planned experiments at CERN, Japan, China and FAIR: a) Do constituent gluons play an important role in the charmonium sector with observable consequences? b) Does QCD predict the existence of glueballs? c) Can they be identified with resonances seen in an experimental search? The Research Unit addresses questions a)-c) above by lattice QCD methods. In principle, lattice QCD methods provide a robust theory framework starting directly from the QCD Lagrangian. These calculations use the Monte Carlo method to estimate strong-interaction physics from the path integral and this provides a well-established way to address a range of physics questions. Many problems involving constituent gluons in QCD remain unsolved, however. Difficulties arise in these calculations as the computational cost to include the quark dynamics in the sampling process is high, while at the same time the statistical fluctuations in the resulting Monte Carlo estimates of observables used to study confined gluons are severe. The three main objectives of this project are: 1. to fully exploit the methods developed in the first funding period for applications to the spectroscopy of glueballs and charmonium as well as of static quark-antiquark pairs with gluonic orbital excitations and to the charmonium radiative decays 2. to further develop and optimize techniques for the solution of the Dirac equation on the lattice and for numerical time integration in the generation of gauge configurations with a robust mathematical foundation 3. to develop a common programming framework based on GPUs to best make use of modern supercomputers. In order to reach these objectives we will combine the expertise of theoretical particle physicists with numerical analysts. The outcome of the research will contribute along with effective field theories to the understanding of present and future experiments.

• DFG Programme: Research Units
• Subproject of: FOR 5269: Future methods for studying confined gluons in QCD
• International Connection: Ireland
• Cooperation Partner: Professor Dr. Michael Peardon