English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

We discuss some problems with the large Nc approximation for nucleons whicharise if the axial coupling of the nucleon to pions is large, g_A \sim Nc.While g_A \sim Nc in non-relativistic quark and Skyrme models, it has beensuggested that Skyrmions may collapse to a small size, r \sim 1/f_pi \simLambda_QCD^{-1}/sqrt(Nc). (This is also the typical scale over which the stringvertex moves in a string vertex model of the baryon.) We concentrate on thecase of two flavors, where we suggest that to construct a nucleon with a smallaxial coupling, that most quarks are bound into colored diquark pairs, whichhave zero spin and isospin. For odd Nc, this leaves one unpaired quark, whichcarries the spin and isospin of the nucleon. If the unpaired quark is in aspatial wavefunction orthogonal to the wavefunctions of the scalar diquarks,then up to logarithms of Nc, the unpaired quark only costs an energy \simLambda_QCD. This naturally gives g_A \sim 1 and has other attractive features.In nature, the wavefunctions of the paired and unpaired quarks might only beapproximately orthogonal; then g_A depends weakly upon Nc. This dichotomy inwave functions could arise if the unpaired quark orbits at a size which isparametrically large in comparison to that of the diquarks. We discuss possibletests of these ideas from numerical simulations on the lattice, for two flavorsand three and five colors; the extension of our ideas to more than three ormore flavors is not obvious, though.

The Dichotomous Nucleon: Some Radical Conjectures for the Large Nc Limit