Parton distribution amplitudes: revealing diquarks in the proton and Roper resonance

TL;DR

This paper provides the first quantum field theory calculation of the leading-twist parton distribution amplitudes for the proton and its radial excitation, revealing diquark correlations and the effects of dynamical chiral symmetry breaking.

Contribution

It introduces a novel quantum field theory computation of proton PDAs, highlighting diquark correlations and the structure of the Roper resonance.

Findings

Proton PDA is broad and concave, with a shifted maximum indicating diquark correlations.

Radial excitation PDA shows interference effects and zeros, characteristic of a radial state.

Diquark correlations account for approximately 60% of the proton's normalization.

Abstract

We present the first quantum field theory calculation of the pointwise behaviour of the leading-twist parton distribution amplitudes (PDAs) of the proton and its lightest radial excitation. The proton's PDA is a broad, concave function, whose maximum is shifted relative to the peak in QCD's conformal limit expression for this PDA; an effect which signals the presence of both scalar and pseudovector diquark correlations in the nucleon, with the scalar generating around 60% of the proton's normalisation. The radial-excitation is constituted similarly, and the pointwise form of its PDA, which is negative on a material domain, is the result of marked interference between the contributions from both types of diquark; particularly, the locus of zeros that highlights its character as a radial excitation. These features originate with the emergent phenomenon of dynamical chiral-symmetry breaking in the Standard Model.