Quarkonium from the Fifth Dimension

Adding fundamental matter of mass mQ 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 ∼ √ gN/mQ, 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-g2N limit; thus these hadrons resemble neither the observed J/Ψ quarkonium states nor ρ mesons.