Probing the quark–gluon interaction with hadrons

Hèlios Sanchis-Alepuz,Richard Williams

doi:10.1016/j.physletb.2015.08.067

Abstract

We present a unified picture of mesons and baryons in the Dyson–Schwinger/Bethe–Salpeter approach, wherein the quark–gluon and quark–(anti)quark interactions follow from a systematic truncation of the QCD effective action and include all its tensor structures. The masses of some of the ground-state mesons and baryons are found to be in reasonable agreement with the expectations of a ‘quark-core calculation’, suggesting a partial insensitivity to the details of the quark–gluon interaction. However, discrepancies remain in the meson sector, and for excited baryons, that suggest higher order corrections are relevant and should be investigated following the methods outlined herein.

Highlights

Hadrons provide a rich experimental environment for the study of the strong interaction, from details of the resonance spectrum to form factors and transition decays via electromagnetic probes
In continuum approaches to quantum chromodynamics (QCD), it is not possible in general to include all possible correlation functions in a calculation, as there are infinitely many of them. This can be viewed as a limitation of continuum approaches, only a finite number of these correlation functions have a significant role in the observable properties of hadrons
It is important to stress that when the 2PI effective action is used to define the truncation at the level of vertex functions, the expansion must be chosen such that the functional derivative (9) can be formally performed to define the chiral-symmetry preserving Bethe–Salpeter equations (BSE) kernels

Summary

Introduction

Hadrons provide a rich experimental environment for the study of the strong interaction, from details of the resonance spectrum to form factors and transition decays via electromagnetic probes. By including a greater number of relevant correlation functions into the system, continuum methods provide an ideal framework to unravel the underlying mechanisms that generate observable effects from the elementary and non-observable degrees of freedom of QCD. This is in contrast to lattice QCD calculations, which can be viewed as theoretical experiments in the sense that, they contain a priori all the dynamics of QCD, it is challenging to single out individual contributions to a particular measurement. Endeavor is feasible, as further increasing the order of the truncation does not increase the technical complexity dramatically

Framework

Results

Summary