Theoretical Approaches to the Spin Structure of the Proton

Many aspects of the structure of the proton are still unknown. One of the most noticeable unanswered question is the one of spin, that is, how can the fundamental degrees of freedom, quarks and gluons, account for the spin of the parent proton? It is known that quarks and gluons carry not only intrinsic but also orbital angular momentum. These two, combined, should in principle should add up to the value 1/2, which characterizes the spin of the proton. The mechanism responsible for this it is yet to be understood. It is not even clear how to define or "separate" the orbital angular momentum from the intrinsic angular momentum of the constituent particles. In recent years, one promising approach to this puzzle known as the spin crisis, is the possibility of accessing the transverse structure of the proton by means of the so called Generalized Parton Distributions (GPDs). These functions appear in the description of exclusive scattering processes. Since GPDs cannot be calculated from first principles, they must be extracted based upon models and experimental data. This dissertation presents the development of a new flexible parametrization, based on a "Reggeized" diquark approach, for chiral-even GPDs. This model is then used to analyze the significance of the different GPDs in some Deeply Virtual Compton Scattering measurements from Jlab; the results from this analysis are extended to the kinematical region relevant at the HERMES experiment. Subsequently, the model is extended to chiral-odd GPDs. With the tool of this model in hand, a study of the flavor dependence of Dirac and Pauli form factors is conducted. The connections v between GPDs and other distribution functions are addressed in the last chapter, in the context of Wigner Distributions and possible probabilistic interpretations.

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