Holographic aspects of three dimensional QCD from string theory

TL;DR

This paper explores holographic models of 3D QCD, focusing on parity anomaly and baryons, revealing new insights into their IR and UV origins and identifying holographic counterparts of baryons as baby Skyrmions.

Contribution

It provides a novel holographic account of the parity anomaly and identifies baryons as baby Skyrmions within a string theory framework, linking IR and UV perspectives.

Findings

Parity anomaly explained via D7 brane embeddings.

Baryons identified as baby Skyrmions in holography.

Correct baryon charges derived from the Witten effect.

Abstract

We study two aspects of 3D QCD with massless fermions in a holographic set-up from string theory, based on D3/D7 branes; parity anomaly and baryons as baby Skyrmions. We first give a novel account of parity anomaly of 3D QCD with odd number of flavors from the IR holographic viewpoint by observing a subtle point in D7 brane embeddings with a given fixed UV theory. We also discuss its UV origin in terms of weakly coupled D-brane pictures. We then focus on the parity-symmetric case of even number of N_F flavors, and study baryons in the holographic model. We identify the monopoles of U(N_F) gauge theory dynamically broken down to U(N_F/2)x U(N_F/2) in the holographic 4 dimensional bulk as a holographic counter-part of 3D baby-Skyrmions for baryons in large N limit, and work out some details how the mapping goes. In particular, we show that the correct baryon charges emerge from the Witten effect with a space-varying theta angle.