The Winner of the Vector-Model Look-Alike Contest

Abstract

In the previous talks, Fritzsch and Barnett have discussed the b quark as a possible explanation of the high-y anomaly. The important question is, how can we incorporate the V+A coupling of the b quark to the u quark in a unified model of weak and electromagnetic interactions. The simplest model with the u-b coupling is the vector model,1 an SU(2) × U(1) model in which both left- and right-handed components of all quarks are in SU(2) doublets. Alas, it is ruled out by neutral current data,2 which shows significant parity violation in the hadronic neutral current. The standard SU(2) × U(l) model,3 in which only left-handed quarks are in doublets, agrees well with neutral current data (see Fig. 1), but has no V+A u-b coupling. In the standard model, the high-y anomaly must be attributed to the Q2 dependence of antiquark and strange-quark distributions in the nucleon induced by QCD. This is probably not enough to explain data.4 Furthermore, as we have heard in Bouchiat’s talk, the standard model may be in trouble with experiments detecting parity violation in atomic physics.