Symmetry principle and constraints on deep inelastic structure functions

It is shown that isospin invariance for hadron states and the usual SU(2) transformation properties of electromagnetic and weak currents (CVC hypothesis) impose strong restrictions on the weak structure functions in terms of the electromagnetic ones. Among others, the inequalities Fvp+FvpFλp+Fλn ⩽ 4, − ∞ ⩽ 12(Fvp−Fvp)−3Fλp⩽32Fλn , are obtained. Furthermore, a quite restrictive scheme is obtained if one adds the following assumptions: 1. (i) Electromagnetic and weak currents are members of a SU(3) octet in the usual sense. 2. (ii) Absence of t-channel exotics. 3. (iii) Currents transform as nonets under U(3). We show that this scheme gives results which are very close to the SU(2) quark-parton light-cone models. In particular, we obtain 14⩽FλpFλn⩽4, Fvp+FvpFλp+Fλn⩽185, −6.11 Fλn ≈ (− 12+97 21)Fλn⩽12(Fvp−Fvp)−3Fvp⩽32Fλn The consequences of adding the SU(3) symmetry of hadron states are also investigated. All the statements which involve weak structure functions require as an additional assumption equality of vector and axial-vector contributions to the scattering amplitudes.