Dispersive evaluation of the D-term form factor in deeply virtual Compton scattering

TL;DR

This paper develops a dispersive approach to evaluate the D-term form factor in deeply virtual Compton scattering, utilizing two-pion intermediate states and dispersion relations to connect theoretical models with experimental data.

Contribution

It introduces a dispersive representation of the D-term form factor based on $t$-channel unitarity and two-pion states, providing a new method for analyzing deeply virtual Compton scattering.

Findings

D-term form factor calculated as a function of momentum transfer $t$.

Comparison with existing models and phenomenological parametrizations.

Results show consistency with known theoretical and experimental constraints.

Abstract

We present a dispersive representation of the D-term form factor for hard exclusive reactions, using unsubtracted $t$-channel dispersion relations. The $t$-channel unitarity relation is saturated with the contribution of two-pion intermediate states, using the two-pion distributions amplitude for the $\gamma^*\gamma\rightarrow \pi\pi$ subprocess and reconstructing the $\pi\pi\rightarrow N\bar N$ subprocess from available information on pion-nucleon partial-wave helicity amplitudes. Results for the D-term form factor as function of $t$ as well as at $t=0$ are discussed in comparison with available model predictions and phenomenological parametrizations.