In gauge-free quark models, quasi-PDFs converge to PDFs with proven sum rules, and the Covariant Parton Model supplies closed-form small-x results that match a Wandzura-Wilczek approximation for the quark energy-momentum tensor form factor.
Nonperturbative renormalization of nonlocal quark bilinears for quasi-PDFs on the lattice using an auxiliary field
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abstract
Quasi-PDFs provide a path toward an ab initio calculation of parton distribution functions (PDFs) using lattice QCD. One of the problems faced in calculations of quasi-PDFs is the renormalization of a nonlocal operator. By introducing an auxiliary field, we can replace the nonlocal operator with a pair of local operators in an extended theory. On the lattice, this is closely related to the static quark theory. In this approach, we show how to understand the pattern of mixing that is allowed by chiral symmetry breaking, and obtain a master formula for renormalizing the nonlocal operator that depends on three parameters. We present an approach for nonperturbatively determining these parameters and use perturbation theory to convert to the MS-bar scheme. Renormalization parameters are obtained for two lattice spacings using Wilson twisted mass fermions and for different discretizations of the Wilson line in the nonlocal operator. Using these parameters we show the effect of renormalization on nucleon matrix elements with pion mass approximately 370 MeV, and compare renormalized results for the two lattice spacings. The renormalized matrix elements are consistent among the different Wilson line discretizations and lattice spacings.
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Lattice QCD extracts the ratio of the third to first Mellin moment of the gluon PDF at 2 GeV from nonlocal operators on an Nf=2+1+1 ensemble.
Renormalized matrix elements for the unpolarized quasi-PDF of the Δ⁺ are computed on two N_f=2+1+1 twisted mass lattice ensembles with pion masses 250 and 330 MeV using momentum smearing.
Reanalysis of lattice data produces proton u(x)-d(x) PDF consistent with global fits within 1 sigma, supporting large-momentum expansion for PDF predictions.
Kinematically enhanced nucleon interpolators improve precision of renormalized quark matrix elements by an order of magnitude at 2.5 GeV with no observed lattice spacing dependence on CLS ensembles.
citing papers explorer
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Quasi Parton Distribution Functions in Covariant Quark Models
In gauge-free quark models, quasi-PDFs converge to PDFs with proven sum rules, and the Covariant Parton Model supplies closed-form small-x results that match a Wandzura-Wilczek approximation for the quark energy-momentum tensor form factor.
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Mellin Moments of the Unpolarized Gluon PDF in the Proton from Nonlocal Operators in Lattice QCD
Lattice QCD extracts the ratio of the third to first Mellin moment of the gluon PDF at 2 GeV from nonlocal operators on an Nf=2+1+1 ensemble.
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Parton distribution functions of $\Delta^+$ on the lattice
Renormalized matrix elements for the unpolarized quasi-PDF of the Δ⁺ are computed on two N_f=2+1+1 twisted mass lattice ensembles with pion masses 250 and 330 MeV using momentum smearing.
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Proton's isovector PDF with updated analysis of large-momentum lattice data
Reanalysis of lattice data produces proton u(x)-d(x) PDF consistent with global fits within 1 sigma, supporting large-momentum expansion for PDF predictions.
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Kinematic enhancement for nucleon interpolators
Kinematically enhanced nucleon interpolators improve precision of renormalized quark matrix elements by an order of magnitude at 2.5 GeV with no observed lattice spacing dependence on CLS ensembles.