Positivity bounds on double parton distributions

TL;DR

This paper derives positivity bounds on double parton distributions in proton-proton collisions, constraining spin correlations and analyzing their stability under QCD evolution, with implications for understanding double hard scattering effects.

Contribution

It introduces new positivity bounds on double parton distributions considering all spin correlations, enhancing the theoretical constraints on these distributions.

Findings

Bounds constrain polarized distributions' size

Bounds can set upper limits on spin correlation effects

Bounds are stable under leading-order DGLAP evolution

Abstract

Double hard scattering in proton-proton collisions is described in terms of double parton distributions. We derive bounds on these distributions that follow from their interpretation as probability densities, taking into account all possible spin correlations between two partons in an unpolarized proton. These bounds constrain the size of the polarized distributions and can for instance be used to set upper limits on the effects of spin correlations in double hard scattering. We investigate the stability of the bounds under leading-order DGLAP evolution to higher scales.