Baryon-Meson Loop Effects on the Spectrum of Non Strange Baryons

TL;DR

This paper investigates how baryon-meson loop effects influence the mass spectrum of non-strange baryons, revealing significant contributions to baryon mass splittings and emphasizing the importance of configuration mixing and residual interactions.

Contribution

It introduces a comprehensive model combining pair-creation and configuration mixing to calculate baryon mass corrections from baryon-meson loops, including a wide range of intermediate states.

Findings

Loop effects account for about half of the nucleon-Delta mass splitting.

Negative-parity excited states are significantly affected by baryon-meson loops.

Model adjustments suggest the importance of string tension and quark mass in fitting baryon spectra.

Abstract

Corrections to the masses of baryons from baryon-meson loops can induce splittings between baryons which are comparable to those arising from the residual interactions between the quarks. These corrections are calculated using a pair-creation model to give the momentum-dependent vertices, and a model which includes configuration mixing to describe the wave functions of the baryons. A large set of baryon-meson intermediate states are employed, with all allowed SU(3)_f combinations, and excitations of the intermediate baryon states up to and including the second band of negative-parity excited states. Roughly half of the splitting between the nucleon and Delta ground states arises from loop effects. The effects of such loops on the spectrum of negative-parity excited states are examined, and the resulting splittings are sensitive to configuration mixing caused by the residual interactions between the quarks. With reduced-strength one-gluon-exchange interactions between the quarks fit to the Delta-nucleon splitting, a comparison is made between model masses and the bare masses required to fit the masses of the states extracted from data analyses. This shows that it is necessary to also adjust the string tension or the quark mass to fit the splitting between the average bare masses of the ground states and negative-parity excited states, and that spin-orbit effects are likely to be important.