A Holographic QCD and Excited Baryons from String Theory

TL;DR

This paper models baryons of all isospins as instanton solitons in a holographic QCD framework derived from string theory, providing insights into their interactions with mesons and extending previous models to excited states.

Contribution

It generalizes holographic QCD models to include all excited baryons and details their couplings with mesons using a soliton approach in a string theory setting.

Findings

Baryons are represented as instanton solitons with locked isospin and spin.

Couplings to axial mesons are dominated by flavor field strength interactions.

The model extends previous work to all excited baryons within a nonrelativistic approximation.

Abstract

We study baryons of arbitrary isospin in a stringy holographic QCD model. In this D4-D8 holographic setting, the flavor symmetry is promoted to a gauge symmetry in the bulk, and produces, as KK modes of the gauge field, pions and spin one mesons of low energy QCD. Baryons of arbitrary isospins are represented as instanton solitons with isospin and spin quantum numbers locked, in a manner similar to the Skyrmion model. The soliton picture leads to a natural effective field theory of arbitrary baryons interacting with mesons. Couplings of baryons to axial mesons, including pions, are dominated in the large $N_c$ limit by a direct coupling to the flavor field strength in five dimensions. We delineate the relevant couplings and determine their strengths. This work generalizes part of hep-th/0701276 and arXiv:0705.2632 [hep-th] to all excited baryons. Due to technical difficulties in introducing relativistic higher spin fields, we perform all computations in the nonrelativistic regime, which suffices for the leading $N_c$ predictions.