Speaker: Fernanda Steffens (NIC, DESY Zeuthen)
Title: Direct Calculation of PDFs in Lattice QCD
Abstract: Parton distributions are usually defined as light-cone correlations in the nucleon. Until recently, however, it was not possible to calculate the distributions in lattice QCD because, unlike spatial correlations, one cannot simulate light-cone correlations in a Euclidian lattice. In 2013, Ji proposed a way to circumvent this restriction, through the use of quark quasi-distributions which are defined as purely spatial correlations. Although they are not the physical distributions, the quark quasi-distributions are related to the quark distributions through a perturbative calculation. Within this procedure, a direct calculation of the distributions in lattice QCD became a possibility, and we present here a high statistics analysis of the x-dependence of the bare unpolarized, helicity and transversity iso-vector parton distribution functions (PDFs) from lattice calculations employing (maximally) twisted mass fermions. The x-dependence of the calculated PDFs resembles those of the phenomenological parameterizations, a feature that makes this approach promising despite the lack of a full renormalization program for them.