Toward a precision calculation of generalized parton distribution functions

Understanding the three-dimensional internal structure of the nucleon is an important goal for nuclear physics. We present the latest lattice-QCD results on the unpolarized and helicity generalized parton distribution functions (GPDs) for the proton, calculated directly at the physical pion mass, using 2+1+1 flavors of highly improved staggered quarks (HISQ) in ensembles generated by MILC Collaboration. These GPDs are calculated using large-momentum effective theory (LaMET) method at skewnesses $xi=0$ and $xi = 0.25$ with multiple transfer momenta. We study and compare the effects of systematic errors by applying hybrid renormalization schemes with leading renormalon resummation and renormalization-group resummation improvement.