Step scaling and the Yang-Mills gradient flow

Understand

The use of the Yang-Mills gradient flow in step-scaling studies of lattice QCD is expected to lead to results of unprecedented precision.

• Step scaling is usually based on the Schr\"odinger functional, where time ranges over an interval [0,T] and all fields satisfy Dirichlet boundary conditions at time 0 and T.
• In these calculations, potentially important sources of systematic errors are boundary lattice effects and the infamous topology-freezing problem.
• The latter is here shown to be absent if Neumann instead of Dirichlet boundary conditions are imposed on the gauge field at time 0.