Quarkonium from the Fifth Dimension

TL;DR

This paper explores the properties of quarkonium in a strongly coupled gauge theory using holographic duality, revealing finite size and unique form factors that differ from QCD expectations.

Contribution

It introduces a holographic analysis of quarkonium with fundamental matter, showing these hadrons are finite in size and have distinctive form factors at large 't Hooft coupling.

Findings

Quarkonium states are finite in size ~ rac{rac{g^2N}{m_Q}}

Certain spin-1 form factors vanish at large g^2N

Hadrons differ from known QCD mesons in form factors and size

Abstract

Adding fundamental matter of mass m_Q to N=4 Yang Mills theory, we study quarkonium, and "generalized quarkonium" containing light adjoint particles. At large 't Hooft coupling the states of spin<=1 are anomalously light (Kruczenski et al., hep-th/0304032). We examine their form factors, and show these hadrons are unlike any known in QCD. By a traditional yardstick they appear infinite in size (as with strings in flat space) but we show that this is a failure of the yardstick. All of the hadrons are actually of finite size ~ \sqrt{g^2N}/m_Q, regardless of their radial excitation level and of how many valence adjoint particles they contain. Certain form factors for spin-1 quarkonia vanish in the large-g^2N limit; thus these hadrons resemble neither the observed J/Psi quarkonium states nor rho mesons.