Baryons from instantons in holographic QCD

TL;DR

This work embeds baryons in a holographic QCD framework (D4/D8) as instantons in a five-dimensional YM–CS theory, with the baryon number identified with instanton number. A unit-baryon soliton is constructed as a BPST instanton of fixed size stabilized by the CS term, and collective-coordinate quantization yields a baryon spectrum that includes nucleons, deltas, and negative-parity states, while incorporating an infinite tower of (axial-)vector mesons through the 5D gauge field. The resulting mass formula exhibits correct large-$N_c$ behavior and captures qualitative features of baryon splittings, though quantitative predictions are sensitive to higher-derivative corrections. The analysis connects the Skyrmion picture to instanton physics in a holographic setting and points to future work on static properties, multi-baryon configurations, and a more complete treatment of higher-derivative terms.

Abstract

We consider aspects of dynamical baryons in a holographic dual of QCD that is proposed on the basis of a D4/D8-brane configuration. We construct a soliton solution carrying a unit baryon number and show that it is given by an instanton solution of four-dimensional Yang-Mills theory with fixed size. The Chern-Simons term on the flavor D8-branes plays a crucial role of protecting the instanton from collapsing to zero size. By quantizing the collective coordinates of the soliton, we work out the baryon spectra. Negative-parity baryons as well as baryons with higher spins and isospins can be obtained in a simple manner.