Over 99% of
the known mass in the world is caused by the strong interaction between
quarks
and gluons. The most successful theory of
this strong force is Quantum Chromodynamics (QCD) which describes how
colored
quarks interact by exchanging gluons. Its notable feature is that
gluons also
carry color charge and hence can interact with other gluons.
QCD has well-developed tools for calculating the rates for interactions between two quarks or gluons. These successful tools are perturbation series in the strong coupling as(q), where q is the momentum transferred during the interaction; this coupling decreases as the momentum q increases and perturbative calculations can reproduce experimental results very accurately.
However, for those interactions that determine the masses of protons, neutrons, and nuclei, the coupling strength as(q) is of order unity. Hence no perturbation series has any chance of convergence. This is the regime of non-perturbative QCD, a broad area of physics that is the focus of my research. My work is guided by the following questions:
QCD has well-developed tools for calculating the rates for interactions between two quarks or gluons. These successful tools are perturbation series in the strong coupling as(q), where q is the momentum transferred during the interaction; this coupling decreases as the momentum q increases and perturbative calculations can reproduce experimental results very accurately.
However, for those interactions that determine the masses of protons, neutrons, and nuclei, the coupling strength as(q) is of order unity. Hence no perturbation series has any chance of convergence. This is the regime of non-perturbative QCD, a broad area of physics that is the focus of my research. My work is guided by the following questions:
- What happens when the QCD interaction is non-perturbatively strong?
- What new phenomena occur and can we quantify these?
- Can we unambiguously test precise calculations of non-perturbative QCD?
- What general lessons on strong coupling physics can we apply to other areas of science?