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Description
Quasi parton distribution functions (QPDFs) are defined in terms of QCD fields at spacelike separations evaluated in matrix elements of hadrons moving with velocity v. These objects can be studied in lattice QCD. In the limit when v approaches the speed of light, QPDFs converge in PDFs. It is insightful to study QPDFs and their convergence in models. In this work, we first study the QPDFs in a broad class of quark models characterized by one common feature, namely the absence of gauge degrees of freedom. We provide general proofs for the convergence and sum rules of the unpolarized quark and antiquarks QPDFs exploring both options γ0 and γ3. We choose the Covariant Parton Model (CPM) to illustrate our results. We derive analytical results for the small-x behavior of QPDFs and the energy-momentum tensor form factor at zero momentum transfer in the CPM. These results are of interest as they correspond to the Wandzura-Wilczek approximation.
