Standard model explanations for the NuTeV electroweak measurements

The NuTeV Collaboration has measured the electroweak parameters sin^2 theta_W and rho in neutrino-nucleon deep-inelastic scattering using a sign-selected beam. The nearly pure neutrino or antineutrino beams that result provide many of the cancellations of systematics associated with the Paschos-Wolfenstein relation. The extracted result for sin^2 theta_W(on-shell) is three standard deviations from prediction. We discuss Standard Model explanations for the puzzle.