Currents nucleon vector

It is found in experiments that the nucleon vector current can to a good approximation be described as the sum of the corresponding valence quark vector currents. For the vector currents of the proton (p) and the neutron (n) we obtain therefore... 

In addition to the dominant PNC interaction given in Eq. (45), there are other smaller PNC interactions that must be considered. First, there is the interaction between the nuclear axial-vector current and the electron vector current from Z exchange. In the limit of nonrelativistic nucleon motion, this interaction is given by the spin-dependent Hamiltonian... 

Since the atomic nucleus consists of nucleons which themselves consist of quarks, in principle the wavefunction of the quarks within the nucleons is required in order to determine appropriate equivalent potentials for the interactions between an electron and the nucleons within the nucleus. The models currently available for the calculation of the substructure of the nucleons, however, allow only for an approximate description of the wavefunctions of the quarks (see for instance [74] for a comparison of a few of these models). One may on the other hand introduce nucleon field operators, which replace the quark field operators in the scattering matrix element (equation (66)), and relate the corresponding vector and axial coupling coefficients in the resulting equivalent potential to empirical data. 

This does not apply for axial currents. They are in contrast to the vector currents renormalised by the strong interaction and therefore only partially conserved. In order to obtain approximate axial coupling coefficients for the nucleons, Cahn and Kane [84] have related the constants for the nncleons to conpling parameters derived from observed decay processes, namely the /3 -decay of the nentron and the similar decay of the hyperon. The axial coupling coefficients of the nncleons read in this approximation as [81,84]... 

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