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S@INT Seminar: "Light-cone PDFs from Lattice QCD"

Martha Constantinou, Temple University
Thursday, August 23, 2018 - 2:00pm
PAT C-421


Lattice QCD (LQCD) is a theoretical non-perturbative approach for
the study of QCD dynamics numerically and from first principles.
For more than a decade, LQCD has been very successful in the calculation of the
hadronic spectrum, making postdictions of well-measured hadronic masses, as
well as, predictions. Nowadays, LQCD is widely used for hadron structure
calculations and is becoming a reliable tool, providing input to the
experimental and phenomenological communities. Over the last years, progress in
the simulation of LQCD has been impressive, driven by improvements in the
algorithms and increase in computational power, that have enabled simulations
to be carried out at parameters very close to their physical values
(physical point).

In this talk I will present recent results for the so-called quasi-PDFs, a new
direct approach to compute parton distributions functions (PDFs)
directly in LQCD. The quasi-PDF approach was introduced by Xiangdong Ji in 2013 and was
intensively developed thereafter. We present results for the unpolarized,
helicity and transversity PDFs calculated at the physical point. A careful
investigation of systematic uncertainties, such as excited states and
renormalization will be presented, that aims at obtaining reliable estimates.
The light-cone PDFs are reconstructed using large momentum effective theory
(LaMET) that allows comparison with phenomenological parameterizations of
experimental data. We find several similarities between the lattice and
phenomenological estimates of PDFs, and demonstrate the importance of
simulations at the physical point. Of particular importance are the
results on the transversity PDFs, that are not well-constrained experimentally,
This presents a major success for the emerging field of direct calculations
of quark distributions using Lattice QCD.

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