Two-Boson Exchange Physics: A Brief Review

TL;DR

This review discusses the current understanding of two-boson exchange effects in elastic electron-proton scattering, highlighting their role in resolving experimental discrepancies and their impact on extracting nucleon form factors.

Contribution

It provides a comprehensive overview of two-boson exchange contributions, including models, experimental methods, and their implications for nucleon structure measurements.

Findings

Two-photon exchange explains discrepancies in form factor measurements.

Positron-proton vs. electron-proton scattering ratios help differentiate models.

Two-boson exchange effects on strangeness form factors are generally small.

Abstract

Current status of the two-boson exchange contributions to elastic electron-proton scattering, both for parity conserving and parity-violating, is briefly reviewed. How the discrepancy in the extraction of elastic nucleon form factors between unpolarized Rosenbluth and polarization transfer experiments can be understood, in large part, by the two-photon exchange corrections is discussed. We also illustrate how the measurement of the ratio between positron-proton and electron-proton scattering can be used to differentiate different models of two-photon exchange. For the parity-violating electron-proton scattering, the interest is on how the two-boson exchange (TBE), \gamma Z-exchange in particular, could affect the extraction of the long-sought strangeness form factors. Various calculations all indicate that the magnitudes of effect of TBE on the extraction of strangeness form factors is small, though can be large percentage-wise in certain kinematics.