The NuTeV Collaboration recently reported a value of ${\sin }^2{\theta }_W$ measured in neutrino-nucleon scattering that is 3 standard deviations above the standard model prediction. This result is derived assuming that (1) the strange sea is quark-antiquark symmetric, $s\left(x\right)=\overline{s}\mathrm{}\left(x\right),$ and (2) up and down quark distributions are symmetric under the simultaneous interchange of $u\leftrightarrow d$ and $p\leftrightarrow n.\mathrm{}$ We report the impact of violations of these symmetries on ${\sin }^2{\theta }_W$ and discuss the theoretical and experimental constraints on such asymmetries.

• Received 2 March 2002

DOI:https://doi.org/10.1103/PhysRevD.65.111103