Model-dependence of the γZ-dispersion correction to the proton's weak charge

We analyze the dispersion correction to elastic parity violating electron-proton scattering due to γZ exchange and theoretical uncertainties associated with this correction. The new Standard Model prediction for the weak charge of the proton in the kinematics of the Q-Weak experiment, QWp = (0.0767±0.0008±0.0020γZ), the latter error being dominated by the uncertainty in the isospin structure of the inclusive cross-section.