CHAPTER 4 - Strangeness-conserving leptonic decays of hadrons. Properties of the ud current

Abstract

The interaction between quark and leptonic currents leads to the leptonic decays of hadrons, which is sometimes referred to as semileptonic decays. This chapter discusses the general properties of the ud current. The ud current is an isovector as the u- and d-quarks are isospinors. Its vector component is G even and the axial component is G odd. There is a profound relationship between vector currents and isovector electromagnetic current of hadrons. The relationship stems from the fact that the three currents form a single isotopic triplet. The chapter also highlights the non-renormalizability of a weak charge. The concept of weak charge gains coherence when the initial and final hadrons of a semi-leptonic decay belong to the same isotopic multiplet. The weak charge determines the strength of the weak vector interaction in the static limit. Although free quarks are encountered, interaction can be found experimentally accurate because the weak charges of the nucleon and quark are identical. In addition, the chapter explains the absolute chiral invariance, which implies conservation of both vector currents and axial currents.