Nucleon QCD sum rules in instanton medium

TL;DR

This paper investigates nucleon QCD sum rules within an instanton medium, showing that a realistic nucleon mass can be obtained when the vacuum is modeled as a mixture of small instantons and gluon fluctuations.

Contribution

It provides a detailed calculation of the nucleon polarization operator in an instanton medium and demonstrates the conditions for realistic nucleon mass solutions.

Findings

Solution exists with nucleon mass close to physical value

Small instantons contribute approximately two-thirds of the vacuum structure

QCD sum rules are consistent with a mixed instanton-gluon vacuum model

Abstract

We try to find the grounds for the standard nucleon QCD sum rules, based on more detailed description of QCD vacuum. We calculate the polarization operator of the nucleon current in the instanton medium. The medium (QCD vacuum) is assumed to be a composition of the small-size instantons and some long-wave gluon fluctuations. We solve the corresponding QCD sum rules equations and demonstrate that there is a solution with the value of the nucleon mass close to the physical one if the fraction of the small size instantons contribution w_s \approx 2/3.