FOR 5269:  Future methods for studying confined gluons in QCD

• Subject Area: Physics ; 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 physics questions for theory are raised by recent and planned experiments: 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?Lattice QCD is a theoretical technique enabling a direct link with QCD physics which relies on large-scale Monte Carlo calculations. 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 used to study confined gluons are severe. The two main objectives of this project are: 1. to develop and optimise new techniques for variance reduction of correlation functions in Monte Carlo calculations with a robust mathematical foundation; 2. to test and begin exploiting these methods to answer the questions a) to c).The Research Unit proposed will develop the new methods needed by combining the inter-disciplinary expertise of lattice QCD physicists and numerical analysts. After developing an advanced framework to address the questions a)-c) computationally, the group will study the glueballs and charmonium states of QCD in detail, using these arenas to test and optimise the new methods while preparing for the next generation of lattice calculations. The new methods will be disseminated effectively to ensure they become widely used in as broad a range of future lattice QCD calculations as applicable.This research will lead to a cross-fertilisation of ideas between the disciplines of theoretical physics and applied numerical analysis, testing developments in molecular dynamics and linear algebra in large-scale physics computations. The Research Unit will foster closer collaboration between these disciplines. The outcome of the research will contribute along with effective field theories to the understanding of present and future experiments.

• DFG Programme: Research Units
• International Connection: Ireland

Projects

• Computing quark propagation in a gluon background (Applicant Frommer, Andreas )
• Coordination Funds (Applicant Knechtli, Francesco )
• Monte Carlo sampling of gluons by molecular dynamics (Applicant Günther, Michael )
• The confined gluon: glueball spectroscopy in the full QCD vacuum (Applicant Schaefer, Stefan )
• The confined gluon: precision spectroscopy with charm quarks (Applicant Knechtli, Francesco )

• Spokesperson: Professor Dr. Francesco Knechtli