Small Instantons in Weakly-Gauged Holographic Models

TL;DR

This paper investigates small instantons in weakly-gauged holographic models, revealing their suppression near the UV boundary due to topological charge conservation, yet uncovers non-trivial instanton-anti-instanton solutions in the bulk.

Contribution

It demonstrates the suppression of small instantons in non-asymptotically-free holographic models and finds novel UV-localized instanton-anti-instanton solutions through conformal transformations.

Findings

Small instantons are highly suppressed near the UV boundary.

Non-trivial instanton-anti-instanton solutions exist in the AdS bulk.

Topological charge conservation prevents instantons from localizing at the UV boundary.

Abstract

Small instantons can play an important role in Yang-Mills theories whose gauge couplings are sizeable at small distances. An interesting class of theories where this could occur is in weakly-gauged holographic models (dual to Yang-Mills theories interacting with strongly-coupled CFTs), since gauge couplings are indeed enhanced towards the UV boundary of the 5D AdS space. However, contrary to expectations, we show that small instantons in these non-asymptotically-free models are highly suppressed and ineffective. This is due to the conservation of topological charge that forbids instantons to be localized near the UV boundary. Despite this fact we find non-trivial UV localized instanton-anti-instanton solutions of the Yang-Mills equations where the topological charges annihilate in the AdS bulk. These analytic solutions arise from a 5D conformal transformation of the uplifted 4D instanton. Our analysis therefore reveals unexpected nonperturbative configurations of Yang-Mills theories when they interact with strongly-coupled CFTs.