Moments of nucleon generalized parton distributions from lattice QCD simulations at physical pion mass

TL;DR

This study computes moments of nucleon generalized parton distributions using lattice QCD at physical pion mass, analyzing multiple ensembles to understand nucleon structure and effects of sea quarks.

Contribution

First lattice QCD calculation of nucleon GPD moments at physical pion mass including strange and charm sea quarks, with detailed analysis of systematic effects.

Findings

Controlled extraction of unpolarized, helicity, and tensor moments.

Computed GPD form factors up to 1 GeV$^2$.

Assessed effects of unquenching and finite volume.

Abstract

We present results for the moments of nucleon isovector vector and axial generalised parton distribution functions computed within lattice QCD. Three ensembles of maximally twisted mass clover-improved fermions simulated with a physical value of the pion mass are analyzed. Two of these ensembles are generated using two degenerate light quarks. A third ensemble is used having, in addition to the light quarks, strange and charm quarks in the sea. A careful analysis of the convergence to the ground state is carried out that is shown to be essential for extracting the correct nucleon matrix elements. This allows a controlled determination of the unpolarised, helicity and tensor second Mellin moments. The vector and axial-vector generalised form factors are also computed as a function of the momentum transfer square up to about 1 GeV$^2$. The three ensembles allow us to check for unquenching effects and to assess lattice finite volume effects.