Progress towards a lattice determination of (moments of) nucleon structure functions

TL;DR

This paper reports on lattice QCD calculations of the lowest moments of nucleon structure functions using Wilson fermions, discussing renormalisation, chiral extrapolation, and continuum limits, with results from quenched and unquenched simulations.

Contribution

It provides new lattice QCD results for nucleon structure function moments with improved methods and explores effects of quenching and chiral extrapolation.

Findings

No significant deviation from linearity in chiral extrapolations.

Quenching effects appear small.

Lowest moment remains larger than experimental values.

Abstract

Using unimproved and non-perturbatively O(a) improved Wilson fermions, results are given for the three lowest moments of unpolarised nucleon structure functions. Renormalisation, chiral extrapolation and the continuum limit of the matrix elements are briefly discussed. The simulations are performed for both quenched and two flavours of unquenched fermions. No obvious sign of deviation from linearity in the chiral extrapolations are found. (This is most clearly seen in our quenched unimproved data, which extends to lighter quark mass.) Possible quenching effects also seem to be small. The lowest moment thus remains too large, so it seems to be necessary to reach smaller quark masses in numerical simulations.