Operator mixing for twist-four and higher contributions

Determine the operator-mixing structure for twist-four and higher-twist matrix elements in lattice QCD, including the effects of mixing with lower-dimensional operators that generate power divergences, to enable their calculation.

Background

The paper explains that higher-twist contributions are important at low Q2 but are difficult to calculate directly on the lattice. Operators may mix with others in the same irreducible representation of the hypercubic group, including lower-dimensional operators that cause power-divergent mixing. Although twist-three matrix elements remain tractable in selected channels, calculations of twist-four and higher contributions have not been pursued because the relevant operator-mixing structure is not completely established.

References

However, corresponding calculations of twist-four matrix elements and beyond have not been pursued, as the operator-mixing structure becomes substantially more complicated and is not fully known.

— Bjorken sum rule down to the elastic region from the lattice  (2610.10006 - Crawford et al., 7 Oct 2026) in Section 1, Introduction