#### Title

Nucleon axial vector form factors and electromagnetic transition amplitudes in perturbative QCD

#### Date Awarded

1991

#### Document Type

Dissertation

#### Degree Name

Doctor of Philosophy (Ph.D.)

#### Department

Physics

#### Advisor

Carl E Carlson

#### Abstract

Values for the normal isovector axial vector form factor g$\sb{\rm A}$(Q$\sp2$) are calculated from the leading order perturbative QCD hard scattering amplitude and some previously reported models for the nucleon distribution amplitude, some of which have been derived from QCD sum rules. The values obtained from each of the distribution amplitudes gives a result that is consistent with the data extrapolated to high momentum transfer. The axial vector form factor is around one and one half times the proton's magnetic form factor in all the models which is also in accord with the data. We also calculate the isoscalar axial vector form factor G$\sbsp{\rm A}{\rm (S)}$(Q$\sp2$). Again we calculate the hard scattering amplitude to leading order in perturbative QCD and convolute that with various models for the nucleon distribution amplitude. There is no data at the present time with which to compare the resulting form factors; however, there is interest in knowing the value since the isoscalar axial vector form factor plays a role in some nonstandard weak interaction models. We find the result to be about half of that for the isovector axial vector form factor. The nucleon-delta electromagnetic transition amplitude is calculated using the same method as in the other cases. However, in this case, the hard scattering amplitude is known, and we use the method of QCD sum rules to develop a model for the delta distribution amplitude. We use these results with the same nucleon distribution amplitudes to get a value for the transition amplitude. We also carry out the same calculation for the lowest-lying negative parity states with both isospin one-half which corresponds to the S$\sb{11}$(1535) and isospin three halves. Compared to the results for the nucleon, the delta, and both the higher-mass negative parity cases are less asymmetric with the isospin three-halves states being consistent with the asymptotic form. The results for the nucleon-delta transition amplitude are found to be consistent with the available data as are the results for the nucleon-S$\sb{11}$(1535) transition amplitude.

#### DOI

https://dx.doi.org/doi:10.21220/s2-74bp-m513

#### Rights

© The Author

#### Recommended Citation

Poor, Jennifer L., "Nucleon axial vector form factors and electromagnetic transition amplitudes in perturbative QCD" (1991). *Dissertations, Theses, and Masters Projects.* Paper 1539623800.

https://dx.doi.org/doi:10.21220/s2-74bp-m513