Improved positivity bound for Deep Inelastic Scattering on transversely polarized nucleon

TL;DR

This paper improves the positivity bound for the transverse asymmetry in Deep Inelastic Scattering by excluding certain photon-nucleon states, providing tighter constraints especially at low or negative asymmetries.

Contribution

The paper introduces an improved positivity bound for the transverse asymmetry $A_2$ by utilizing the non-participation of specific spin states, refining previous bounds.

Findings

Enhanced positivity bound for $A_2$ applicable at low or negative asymmetries

The bound excludes contributions from total spin 3/2 photon-nucleon states

Useful for analyzing asymmetries in neutron and low-$x$ regimes

Abstract

The positivity bound for the transverse asymmetry $A_2$ may be improved by making use of the fact, that the state of a photon and a nucleon with total spin 3/2, does not participate to the interference. The bound is therefore useful in the case of a longitudinal asymmetry small (say, at low $x$) or negative (like in the neuteron case).