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PHY Theoretical Physics Seminar

Abstract: Electromagnetic form factors give Lorentz invariant information about the electromagnetic charge distributions inside hadrons. They are thus a key probe of the dynamics of QCD in the low-energy, nonperturbative régime. Importantly, it is well known that because of its characteristically light mass, the pion plays an important role in low-energy observables.

In particular, the effects of implementing pion loop corrections at the hadron level (as opposed to the quark level) will be discussed. I will show results for electromagnetic form factors calculated in the NJL Model; in particular, one obtains an improved prediction of the predicted Hyperon Magnetic moment when the pion loop effects are implemented in this way. One important input into this calculation is the pion form factor itself. Modern extractions of the pion form factor for moderate values of the photon virtuality (above about 0.3 GeV2) arise from a model dependent extraction from pion electro-production data.

In the second half of the talk, a simple model of pion electro-production, will be described and used to examine the model dependence of the extraction method. In the context of this simple model, the extracted form factor is systematically overestimated.