Holographic glueball structure

We perform a systematic analysis of the scalar glueball correlation functions in both the hard-wall and dilaton soft-wall approximations to the holographic QCD dual. The dynamical content of the holographic correlators is uncovered by examining their spectral density and by relating them to the operator product expansion, a dilatational low-energy theorem and a recently suggested two-dimensional power correction associated with the short-distance behavior of the heavy-quark potential. This approach provides holographic estimates for the three lowest-dimensional gluon condensates, the two leading moments of the instanton size distribution in the QCD vacuum and an effective UV gluon mass. A remarkable complementarity between the nonperturbative physics of the hardand soft-wall correlators emerges, and their ability to describe detailed QCD results can be assessed quantitatively. We further provide the first holographic estimates for the decay constants of the 0++ glueball and its excitations. The hard-wall background turns out to encode more of the relevant QCD physics, and its prediction fS ∼ 0.8 − 0.9 GeV for the phenomenologically important ground state decay constant agrees inside errors with recent QCD sum rule and lattice results.