Theory Seminar: Alec Hannaford-Gunn

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Speaker: Alec Hannaford-Gunn (University of Adelaide)

Title: A lattice QCD calculation of the off-forward Compton amplitude and generalised parton distributions

Abstract: Generalized parton distributions (GPDs) are observables that provide a unique window into hadron structure, including the spatial distribution of hadron constituents and their spin decomposition. Despite their importance, GPDs remain elusive: they are difficult to determine experimentally, and lattice QCD calculations have provided only limited constraints on their behavior. I will give an overview of a novel method to determine GPD properties in lattice QCD currently being implemented by the CSSM/QCDSF collaboration. We have extended Feynman-Hellmann methods—previously used to calculate the forward Compton amplitude—to determine the off-forward Compton amplitude for soft momentum transfer in the range -t ∈[0.3, 2.2]GeV2. As with the physical scattering amplitude, our lattice Compton amplitude is dominated by GPD contributions at high energies. Therefore, I will also present our efforts to constrain GPD properties from this calculation, especially our determination of the GPD moments An,0(t) and Bn,0(t) for n=2,4.