J. T. Londergan

Flavor and Charge Symmetry in the Parton Distributions of the Nucleon

Recent calculations of charge symmetry violation (CSV) in the valence quark distributions of the nucleon have revealed that the dominant symmetry breaking contribution comes from the mass associated with the spectator quark system. Assuming that the change in the spectator mass can be treated perturbatively, we derive a model independent expression for the shift in the parton distributions of the nucleon. This result is used to derive a relation between the charge and flavor asymmetric contributions to the valence quark distributions in the proton, and to calculate CSV contribution to the nucleon sea. The CSV contribution to the Gottfried sum rule is also estimated, and found to be small.

Composite vertices that lead to soft form factors

The momentum-space cutoff parameter {Lambda} of hadronic vertex functions is studied in this paper. We use a composite model where we can measure the contributions of intermediate particle propagations to {Lambda}. We show that in many cases a composite vertex function has a much smaller cutoff than its constituent vertices, particularly when light constituents such as pions are present in the intermediate state. This suggests that composite meson-baryon-baryon vertex functions are rather soft, i.e., they have {Lambda} considerably less than 1 GeV. We discuss the geometrical origin of this softening of form factors as well as the implications of our findings on the modeling of nuclear reactions.