Contributor info: Prof. Gerrit Schierholz

Gerrit Schierholz

SciPost Phys. Proc. 6, 011 (2022) · published 31 May 2022 | Toggle abstract · pdf

Three hard problems! In this talk I investigate the long-distance properties of quantum chromodynamics in the presence of a topological theta term. This is done on the lattice, using the gradient flow to isolate the long-distance modes in the functional integral measure and tracing it over successive length scales. It turns out that the color fields produced by quarks and gluons are screened, and confinement is lost, for vacuum angles |theta| > 0, thus providing a natural solution of the strong CP problem. This solution is compatible with recent lattice calculations of the electric dipole moment of the neutron, while it excludes the axion extension of the Standard Model.

K.U. Can, A. Hannaford-Gunn, R. Horsley, Y. Nakamura, H. Perlt, P.E.L. Rakow, E. Sankey, G. Schierholz, H. Stuben, R.D. Young, J.M. Zanotti

SciPost Phys. Proc. 6, 003 (2022) · published 31 May 2022 | Toggle abstract · pdf

A major objective of lattice QCD is the computation of hadronic matrix elements. The standard method is to use three-point and four-point correlation functions. An alternative approach, requiring only the computation of two-point correlation functions is to use the Feynman-Hellmann theorem. In this talk we develop this method up to second order in perturbation theory, in a context appropriate for lattice QCD. This encompasses the Compton Amplitude (which forms the basis for deep inelastic scattering) and hadron scattering. Some numerical results are presented showing results indicating what this approach might achieve.