Two-boson exchange corrections in lepton–nucleon scattering

This project was devoted to the study of radiative corrections arising from the exchange of two gauge bosons in lepton–nucleon scattering. Its main goal was to quantify how such higher-order effects modify measured cross sections and, consequently, how they affect the extraction of nucleon-structure information from precision experiments.

From the technical point of view, the main challenge of the project was the calculation of two-boson-exchange corrections from loop box diagrams, where the result depends sensitively on the internal structure of the nucleon. In the case of elastic electron–proton scattering, the two-photon-exchange contribution was evaluated both in a data-driven Bayesian neural-network framework and in a hadronic model based on box diagrams with nucleon and Δ-resonance intermediate states. For charged-current neutrino–nucleon scattering, the key task was to compute the electroweak Wγ box correction in a gauge-consistent way, using nucleon form factors to model the off-shell hadronic vertices and estimating the interference with the Born amplitude. This required combining field-theoretical loop calculations with phenomenological input on nucleon structure, and it was precisely this interplay between radiative corrections and hadronic modeling that constituted the most demanding part of the project.

In elastic electron–proton scattering, we investigated the two-photon-exchange contribution and compared two complementary approaches: a data-driven neural-network framework and a hadronic model. This analysis showed that both methods give consistent predictions in an important intermediate kinematic region, while also revealing where model dependence becomes significant. The study demonstrated that two-photon exchange is an essential ingredient in precision analyses of proton form factors and related observables, including proton-radius extractions.

In charged-current neutrino–nucleon scattering, we evaluated the two-boson-exchange correction generated by electroweak box diagrams, in particular the mixed Wγ contribution to quasielastic reactions. We showed that these effects are typically at the percent level, with larger corrections for electron neutrinos and antineutrinos than for muon flavors. This is important for modern oscillation experiments, where even small flavor-dependent differences in cross sections can become a relevant source of systematic uncertainty.

Together, these works provided a consistent picture of how two-boson-exchange effects enter both electromagnetic and weak lepton–nucleon processes. The project helped clarify the size and phenomenological relevance of these corrections in regimes important for proton-structure studies and precision neutrino physics.

Funding: [place for funding information]

References:
Phys. Rev. C 88, 065205 (2013)
Phys. Lett. B 735, 299–303 (2014)

Collaborators: N/A

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