We present the first Coulomb-gauge calculation of the nucleon unpolarized parton distribution functions (PDFs) at the physical pion mass. Both the isovector and connected isoscalar channels are computed within the large-momentum effective theory (LaMET) framework on a $2+1$ flavor ensemble with lattice spacing $a = 0.076$ fm. By employing kinematically enhanced interpolating operators, we...
We report a state-of-the-art lattice QCD calculation of the total gluon helicity contribution to the proton spin, $\Delta G$. After extrapolating to the continuum limit, $\Delta G$ is found to be $\Delta G=0.231(17)^{sta.}(44)^{sym.} at the $\overline{\mathrm{MS}}$ scale $\mu^2=10\ \mathrm{GeV}^2$, which constitutes approximately 46(9)% of the proton spin. In addition, we will also provide a...
Gluon parton distribution functions (PDFs) from large momentum effective theory (LaMET) have remained in poor statistical precision compared to non-singlet PDFs due to their correlators coming solely from disconnected diagrams. One method to improve the long distance signal is to remove the Wilson lines from the correlators, which are present solely to maintain gauge invariance, and compute...
We calculate the ``kinematic'' corrections $t/P_z^2$ and $m_N^2/P_z^2$ to the short distance expansion of gauge-invariant nonlocal quark-antiquark operators sandwiched between nucleon states with different momenta. Here $t$ is the momentum transfer, $m_N$ is the nucleon mass and $P_z$ is the momentum component in the direction of the quark-antiquark separation, which is assumed to be...
This talk presents an extraction of Mellin moments of the proton unpolarized generalized parton distributions (GPDs) at nonzero skewness from lattice QCD. The analysis builds on the recent studies of GPDs at nonzero skewness, which, together with the polynomiality relations and short-distance factorization matching, connect the moments to generalized form factors. The present method uses...
Understanding and controlling systematic uncertainties is one of the main challenges in lattice QCD calculations. In this work, we investigate the momentum transfer ($t$) dependence of Mellin moments for unpolarized proton generalized parton distributions (GPDs) at zero skewness. The ground-state matrix elements are extracted using plateau fits and subsequently renormalized using the double...
We present a lattice QCD determination of the Mellin moments of the unpolarized gluon parton distribution function in the proton. The analysis is based on matrix elements of nonlocal gluon operators coupled to momentum-boosted proton states. The calculation relies on an $N_f=2+1+1$ ensemble of maximally twisted mass fermions with clover improvement and the Iwasaki-improved gauge action, at a...
The instanton liquid model is believed to capture the main features of vacuum QCD dynamics. Recently, multiple predictions for hadron structure functions have been derived and compared with experimental measurements and lattice QCD calculations, showing general agreement. In order to explore the precision of the instanton liquid model, one has to compare its predictions with non-perturbative...
Partons provide a natural language for hadron structure at high energies in QCD. However, direct light-front (LF) quantization leads to severe infrared singularities. These divergences reflect the absence of an intrinsic IR scale and nontrivial vacuum structure, thus placing QCD at a critical point. As a result, well-defined parton distributions are constructed through renormalization prior to...
