Physical Review D
The gamma Z-box diagram for parity violating elastic e-p scattering has recently undergone a thorough analysis by several research groups. Though all now agree on the analytic form of the diagram, the numerical results differ due to the treatment of the structure functions, F-1,2,3(gamma Z) (x, Q(2)). Currently, F-1,2,3(gamma Z)(x, Q(2)) at low Q(2) and W-2 must be approximated through the modification of existing fits to electromagnetic structure function data. We motivate and describe the modification used to obtain F-1,2(gamma Z)(x, Q(2)) in our previous work. We also describe an alternative modification and compare the result to our original calculation. Finally, we present a new modification procedure to acquire F-3(gamma Z) (x, Q(2)) in the resonance region and calculate the axial contribution to the gamma Z-box diagram. Details of these modifications will illuminate where discrepancies between the groups arise and where future improvements can be made.
Rislow, B. C., & Carlson, C. E. (2013). Modification of electromagnetic structure functions for the γ Z-box diagram. Physical Review D, 88(1), 013018.